Razionale Armando
Professore Ordinario
Università degli Studi di Pisa
armando.viviano.razionale@unipi.it
Sito istituzionale
SCOPUS ID: 6503910490
Orcid: 0000-0001-7110-3857
Pubblicazioni scientifiche
Abstract: Polyether ether ketone (PEEK) is a thermoplastic polymer that presents notable thermal resistance, high mechanical strength, biocompatibility, durability, chemical resistance, and low density. PEEK can be additively manufactured by Power Bed Fusion (PBF) and Material Extrusion (ME) techniques. However, the latter is easier to operate and less expensive than the first solution. Printing parameters and thermal post-processing are fundamental aspects to improve the mechanical and thermal properties of the printed part. In the present study, the effects of two distinct thermal post-processing treatments and three different printing speeds on the mechanical properties of PEEK samples produced by ME were investigated. 45 specimens were manufactured, 15 for each printing speed and 5 for each thermal treatment. The results demonstrated that for the as-printed condition, higher printing speeds produced the greatest outcomes in terms of ultimate tensile strength and elastic modulus, whereas the lowest printing speed produced the maximum strain at break. The thermal post-processing treatments revealed that the one carried out at lower temperatures resulted in negligible changes, while the other significantly improved the mechanical performance of the material. The study's findings provide a solid foundation for printing and post-processing a cutting-edge polymer like PEEK to maximize its potential.
Keywords: Material Extrusion | Mechanical Properties | PEEK | Printing Speed | Thermal Post-Processing
Abstract: Full-field methods can significantly improve measurement quality in experimental dynamic analysis, which is a critical issue in the industry. Optical methods based on digital image correlation (DIC) are widely used in this regard. This paper aims to present an experimental setup to perform full-field vibration measurements using off-the-shelf components costing tens or hundreds of euros rather than thousands. This allows for the construction of multiple measurement systems with a small investment, giving students hands-on experience. The system’s inherent low cost, ease of assembly, and ease of use ensure that the student can handle the system from the design stage to the setup stage, and finally to the testing stage. A simple Matlab app was developed to set up and control the test, analyze data and display the results. The system’s modularity allows it to further extend measurement capabilities over time, performing 2D measurements or more complex 3D measurements under single or multiple inputs. A prototype of the proposed system was assembled and tested on a planar specimen for 2D DIC measurements. The total cost of the equipment was less than 250 €. The setup was validated for geometrically complex torsional deformed shapes up to 660 Hz.
Keywords: Digital Image Correlation | Educational Test Bench | Full Field Vibration Measurement
Abstract: Aim: The objective of this research has been to apply a specific simulation to a patient to assess the biomechanical consequences of rotating an upper canine tooth through different attachment–aligner configurations and to predict the most efficient design using a three-dimensional finite element model of a full maxillary arch of a specific patient. Materials and methods: This was obtained by combining Cone-Beam Computed Tomography (CBCT) with the aim of reconstructing tooth roots and bone tissues, and Surface Structured-Light Scanning for creating digital tooth crown models from the patient’s impressions. This model was imported into the finite element solver (Ansys® 17). Three different attachment–aligner combinations were created through the exploitation of computer-aided design (CAD) procedures, i.e., without attachments, with a couple of attachments and with an attachment and a pressure point. For each simulation, the resulting force–moment (MF) system applied by the aligner to the target tooth, as well as the tooth displacement and rotation, was computed using a workstation based on Intel Xeon CPU E3-1245 v3@3.40 GHz and 16 GB RAM. Simulations reported that by adding the pressure point and the attachment to the standard aligner the amount of Moment z (Mz) delivered to the tooth increased almost two times. Results and conclusions: The maximum tooth displacement (0.85 mm) was obtained with the attachment and pressure point aligner, while the lowest (0.058 mm) was obtained with use of a couple of attachments. Both the attachment and the pressure point have the potential to enhance the appliance’s effectiveness. Particularly, the pressure point showed a higher influence on the load absolute value. The method applied in the present study should be used to retrieve the best design configuration for each patient and specific tooth movement
Keywords: aligners | digital workflow | finite element analysis | malocclusion | orthodontic movement | three-dimensional diagnosis and analysis | three-dimensional tooth movement
Abstract: The growing attention of people to aesthetics has led to a greater demand for dental whitening treatments. Several solutions can be utilized to obtain the desired visual whiteness of teeth but, according to literature, at-home supervised treatments are the standard in dental bleaching. They require soft plastic trays to contain a whitening gel, with active chemical agents, and keep it in contact with the patient’s teeth. The fitting, comfort, and tightness of trays play a fundamental role in the treatment. Any gel leakage can compromise the effectiveness of the treatment and damage soft tissues. Commonly, the trays are ready-made or based on physical dental impressions and manually modified by the dental technician. These procedures have low repeatability and do not always ensure high accuracy. This work presents an automatic digital algorithm to design customized whitening trays. Starting from a digital scan acquisition of the patient’s dental arches, it generates the 3D models of the bespoke trays, in approximately two minutes per arch, ready to be produced by additive manufacturing and thermoforming technologies. The evaluation of the method involved 20 patients. The results emphasize that the custom trays were comfortable and ensured high levels of tightness and fitting.
Keywords: automatic product design | custom teeth trays | dental whitening | digital process
Abstract: Lattice structures play an increasingly crucial role in Additive Manufacturing (AM) to enhance the performance of parts for industrial and biomedical applications. Among AM technologies, VAT photopolymerization is one of the most suitable in producing shapes characterized by a good resolution and fine details as required for lattice structures. High stiffness and strength photoresins are commonly adopted when strut-and-node lattice structures, based on stretch-dominated unit cells, are printed. However, this choice can lead to brittle and sudden structural failures, undermining the use of these structures due to safety reasons. This work evaluates the effect of chemical post-processing on the deformation behavior and the tensile properties of SLA strut-and-node-based lattice structures. FCC (Face-Centered Cubic) lattice structures with two different layer heights were tested, and a highly deformable UV resin was used as a coating product. Results evidenced an increase in specimen elongation up to 64% for coated FCC lattice structures with respect to as printed samples. Chemical post-processing based on resin coating demonstrated to be an effective solution to get additively manufactured strut-and-node-based lattice structures characterized both by high strength and high strain.
Keywords: Coating post-processing | Lattice structures | Tensile properties | VAT photopolymerization
Abstract: In this paper, a semi-automatic procedure to perform point clouds registration is presented. The method was developed for upper limb 3D scanning. During the acquisition, several frames are acquired from different points of view, to obtain a full 360° acquisition of the arm. Each frame stores both the point clouds coordinates and the corresponding RGB image. During post-processing, the RGB image is elaborated through a neural network, to detect relevant key points of the hand, which are then projected to the point clouds. The corresponding key points detected from different acquisitions are then used to automatically obtain a rough 3D rotation that aligns the point clouds corresponding to different perspectives in a common reference frame. Finally, the registration is refined through an iterative closest point algorithm. The method was tested on actual arm acquisitions, and the registration results are compared with the conventional fully manual 3-2-1 registration procedure, showing promising results of the proposed method.
Keywords: Neural network | Semi-automatic registration | Upper limb 3D scan
Abstract: The demand for orthodontic and aesthetic treatments, aimed at having healthier teeth and more beautiful smiles, is increasingly growing. The devices on which these treatments are based must be rigorously bespoke for each patient. This is amplifying the need to develop digitized workflows, ranging from scanning to Additive Manufacturing (AM). The present work proposes an alternative workflow for designing and manufacturing orthodontic aligners, also known as clear aligners, starting from the intraoral scanning of the patient’s dentition. Orthodontic aligners are an alternative to metal brackets to correct dental malocclusions and they are often preferred by the patients because of their lower impact on facial aesthetics and for their higher comfort. The orthodontic treatments based on the aligners utilize a series of aligners, each one with a geometry slightly different from the previous one. The use of the single aligners is aimed to apply a force to the teeth and gradually aligning them until the end of the treatment. The workflow we propose in the present study is based on the following three main stages: intraoral scanning of the patient’s dentition, design of the aligners through a semi-automatic algorithm, and the direct additive manufacturing of the aligners through VAT photopolymerization technique. The possibility to directly additive manufacturing the aligners allows us to rethink the current orthodontic treatments. The aligners geometry can be re-designed, with the possibility of locally manipulating the thickness. This approach would allow the regulation of the amount of force applied locally to the tooth, thus optimizing the treatment and its duration. A feasibility study of the proposed workflow is reported in the present paper, with a focus on the semi-automatic design algorithm and on the additive manufacturing process of the aligners.
Keywords: Additive Manufacturing | Bespoke Medical Devices | Dental Appliances | Design Algorithms for Medical Applications | DfAM
Abstract: In the field of optical 3D scanning for healthcare applications, low-cost depth cameras can be efficiently used to capture geometry at video frame rates. However, the complete reconstruction of anatomical geometries remains challenging since different scans, collected from multiple viewpoints, must be aligned into a common reference frame. This paper proposes a fully automatic procedure to align scans of the upper limb patient’s anatomy. A 3D optical scanner, obtained by assembling three depth cameras, is used to collect upper limb acquisitions. A relevant dataset of key points on the hand and the forearm geometry is then determined and used to automatically obtain a rough 3D alignment of the different scans. Hand key points are identified through a neural network, which works on RGB images captured by the depth cameras; forearm key points are recognized by directly processing the point clouds through a specifically designed algorithm that evaluates the skeleton line of the forearm. The approach was tested on forearm acquisitions, and the results were compared to alternative alignment methodologies.
Keywords: 3D optical scanning | automatic point clouds alignment | depth cameras | upper limb anatomy
Abstract: The 3D reconstruction of upper limb anatomy plays a significant role in many biomedical fields such as ergonomics, motion rehabilitation, and prosthesis design. In the last few years, the technical advancement of consumer-grade depth cameras has supported the development of portable and low-cost optical 3D body scanners for healthcare applications. The real-time scanning of human body parts, however, still represents a complex task due to the non-stationary nature of the scanning target. This issue imposes that the scanning time must be reduced as much as possible to minimize scanning artifacts. In this regard, depth cameras can capture geometrical information at video frame rates, thus guaranteeing fast acquisition times. Furthermore, the simultaneous use of multiple sensors would minimize undercut geometries, which impair the 3D reconstruction’s completeness. In this work, a portable 3D optical scanner has been developed by rigidly assembling three Intel® RealSense™ D415 depth cameras on a lightweight circular frame. The three sensors are mutually calibrated, by using a 3D printed calibration specimen, to simultaneously align acquisitions from the three different camera viewpoints for each scanner pose. The system’s effectiveness has been assessed by acquiring the geometry of both a plaster hand and a human hand and comparing the results with those obtained by a high-end stationary structured light scanner. The developed system represents a low-cost handheld alternative to existing body scanners for collecting and storing 3D anatomical data, which can be used in the design process of bespoke medical devices.
Keywords: 3D optical scanning | D415 Intel® RealSense™ | Depth-camera | Upper Limb Reconstruction
Abstract: Typical additive manufacturing (AM) processes for producing metal and ceramic parts are highly energy-consuming and expensive to install and maintain. On the other hand, material extrusion AM (MEAM) technologies are conventionally used to produce polymeric parts but only marginally to process metallic materials. A feasible alternative is to process polymeric filaments loaded with metal particles. Debinding and sintering processes are then required to join the metal particles and obtain the final parts. In recent years, highly filled metal filaments consisting of a polymer loaded with a high concentration of metal powder have been commercialized for this purpose. In this study, the printability of a commercial CuSn12 filament was investigated by evaluating the influence of the process parameters on the density, shrinkage, porosity, and mechanical properties of the additively manufactured samples using a low-cost desktop 3D printer. Parameters such as the flow rate and ironing had the greatest influence on the density of the green samples. The correct selection of these parameters may reduce shrinkage after sintering. Furthermore, the obtained bronze had a notable ultimate tensile strength (mean value of 107 MPa), high stiffness (E values range from 38 to 50 GPa), and a greater elongation at break (mean value of 13%) than that of cast bronze of the same CuSn12 type. In this case, the extrusion pattern and ironing had the most significant influence on the final mechanical performance. The study provides insights into the use of highly filled bronze filaments combined with MEAM to produce functional parts for engineering applications.
Keywords: Highly filled bronze filament | Mechanical properties | Metal material extrusion | Printing parameters | Shrinkage
Abstract: Primary dentition is crucial in influencing the emergence of permanent teeth. Premature primary tooth loss can result in undesired tooth motions and space loss in the permanent dentition. Typically, fixed or removable dental appliances are adopted to maintain edentulous space until the eruption of permanent teeth. However, traditional space maintainers have limitations in terms of variability in tooth anatomy, potential allergic reactions in some individuals (i.e., nickel sensitivity), difficulties in maintaining oral hygiene, and patient acceptance. The present study introduces a fully digital framework for the design and manufacturing of customized pediatric unilateral space maintainers using generative algorithms. The proposed approach overcomes the current challenges by using a biocompatible resin material and optimizing the device’s size, design, and color. The methodology involves intraoral scanning, surface selection, and trim, generative 3D modeling, finite element analysis (FEA), and additive manufacturing (AM) through vat photopolymerization. FEA results demonstrate the device’s mechanical performance and reliability, while additive manufacturing ensures design freedom, high resolution, surface finishing, dimensional accuracy, and proper fit. The mechanical interlocking system facilitates easy and effective positioning of the device. This digital approach offers the potential for wider usage of space maintainers and can be further validated through experimental assessments and clinical studies.
Keywords: 3D printing | digital space maintainer | FEA analysis | generative design | pediatric dentistry
Abstract: igital representations of anatomical parts are crucial for various biomedical applications. This paper presents an automatic alignment procedure for creating accurate 3D models of upper limb anatomy using a low-cost handheld 3D scanner. The goal is to overcome the challenges associated with forearm 3D scanning, such as needing multiple views, stability requirements, and optical undercuts. While bulky and expensive multi-camera systems have been used in previous research, this study explores the feasibility of using multiple consumer RGB-D sensors for scanning human anatomies. The proposed scanner comprises three Intel® RealSenseTM D415 depth cameras assembled on a lightweight circular jig, enabling simultaneous acquisition from three viewpoints. To achieve automatic alignment, the paper introduces a procedure that extracts common key points between acquisitions deriving from different scanner poses. Relevant hand key points are detected using a neural network, which works on the RGB images captured by the depth cameras. A set of forearm key points is meanwhile identified by processing the acquired data through a specifically developed algorithm that seeks the forearm’s skeleton line. The alignment process involves automatic, rough 3D alignment and fine registration using an iterative-closest-point (ICP) algorithm expressly developed for this application. The proposed method was tested on forearm scans and compared the results obtained by a manual coarse alignment followed by an ICP algorithm for fine registration using commercial software. Deviations below 5 mm, with a mean value of 1.5 mm, were found. The obtained results are critically discussed and compared with the available implementations of published methods. The results demonstrate significant improvements to the state of the art and the potential of the proposed approach to accelerate the acquisition process and automatically register point clouds from different scanner poses without the intervention of skilled operators. This study contributes to developing effective upper limb rehabilitation frameworks and personalized biomedical applications by addressing these critical challenges.
Keywords: 3D optical scanning | automatic point cloud alignment | depth cameras | neural network | upper limb anatomy
Abstract: Material Extrusion Additive Manufacturing (MEAM) for metals is becoming increasingly appealing compared to other metal AM techniques, which are typically energy-intensive and require equipment expensive to install and maintain. In MEAM a polymeric feedstock filled with metal particles is extruded through a heated nozzle; subsequently, the 3D-printed green parts are debound and sintered. This study investigates the feasibility of producing functional Inconel-718 components with a commercial filament and a desktop printer, using a one-step thermal debiding and sintering procedure. To this purpose, the feedstock was extensively characterized, and optimal printing parameters were determined using the design of experiment technique and statistical analysis. Then tensile specimens were printed, debound, sintered and their mechanical and physical properties were measured. The specimens reached a maximum relative density of 83.4% and a maximum ultimate tensile strength of 223 MPa. A decrease in the debinding heat rate was required to avoid macro-void formation.
Abstract: This paper explores how the examination of additively manufactured auxetic componentry can be applied in human-centred design settings with particular focus on biomedical products. Firstly, the design applications of auxetics are detailed followed by a review of the key problems facing practical researchers in the field with the treatment of boundary conditions identified as a key issue. The testing setup that is then introduced utilises a novel method of part mounting and facilitates optical analysis and real-time force–displacement measurements. A study is advanced that analyses three different auxetic structures (re-entrant, chiral, and semi-rigid), a set of samples of which were additively manufactured in flexible TPU material. A range of parameters were varied across the three designs including interior geometry and wall thicknesses in order to demonstrate the effectiveness of the setup for the examination of the different structures. The results from these examinations are subsequently discussed and a number of suggestions made regarding how this kind of analysis may be integrated into novel design development workflows for achieving human-centred biomedical devices which often require detailed consideration of ergonomic and usability factors.
Keywords: Auxetics | Biomedical applications | Human-centred design | Mechanical testing
Abstract: Additive manufacturing is a technology gaining ground in fields where a high degree of product customization is required; in particular, several aspects need to be explored concerning traditional technologies, such as the variety of materials and their consumption. It also remains to be clarified whether these technologies can contribute to the ecological transition when applied in healthcare. This study compares two technologies for producing clear dental aligners: thermoforming and direct 3D printing. The former method thermoforms a polymeric disc over 3D-printed, customized models. The second, more innovative approach involves directly printing aligners using Additive Manufacturing (AM), specifically applying Digital Light Processing (DLP) technology. The study conducts a comparative Life Cycle Assessment (LCA) analysis to assess the environmental impact of these two different manufacturing processes. The research results highlight that adopting direct printing through AM can bring advantages in terms of environmental sustainability, thanks to the reduction in raw materials and electricity consumption. These drops are drivers for the decreased potential environmental impacts across all impact categories considered within the EF 3.1 method. Furthermore, lowering the amount of raw material needed in the direct printing process contributes to a notable decrease in the overall volume of waste generated, emphasizing the environmental benefits of this technique.
Keywords: additive manufacturing | healthcare | life cycle assessment | sustainability
Abstract: This study presents an alternative process for designing and manufacturing customized trays for dental-whitening treatments. The process is based on a digitized approach consisting of three main stages: design of a reference model, its manufacturing by AM, and thermoforming of the tray. The aim of the study was to develop a high-performance tray, able to guarantee comfort, safety, and efficacy for whitening treatments. To evaluate the patient’s experience, some tests under real operating conditions were performed. Twenty people carried out a nighttime treatment of 14 days. Each patient was asked to assess the overall level of satisfaction and the comfort of the tray and its ability to retain the gel. Tooth whitening was also determined according to the VITAPAN scale. All patients involved in the study were satisfied and provided positive feedback about comfort and tightness of the tray. At the end of the treatment, 15 out of 20 patients achieved shade A1 on the VITAPAN scale. The mean improvement in color shades was about 7. These results confirmed the great potential of the proposed dental tray. Its use was proven to guarantee a high level of quality, flexibility, and customization of dental-whitening treatments, improving comfort, safety, and efficacy.
Keywords: additive technologies | bespoke dental trays | custom design | dental engineering | digital manufacturing | esthetic dentistry | tooth whitening
Abstract: The 3D reconstruction of upper limb anatomy plays a significant role in many biomedical fields as ergonomics, motion rehabilitation, prosthesis design. Conventional manual measurements have been progressively replaced by 3D optical scanning in collecting and storing 3D anatomical data, thus increasing reliability and data accuracy, shortening, at the same time, the overall acquisition process. However, the real-time scanning of human body parts still represents a complex task since it is challenging to keep the arm in a stable position and avoid artifacts in the collected data. Also, optical undercut geometries often impair the 3D reconstruction’s completeness. In this paper, a compact and low-cost 3D scanning system has been developed by integrating three D415 Intel RealSense cameras. The three depth cameras have been assembled in a circular rig to define a lightweight handheld scanner capable of carrying out 3D data acquisition in different scenarios. The optical system has been validated through anthropometric measurements on different subjects.
Keywords: 3D scanning | D415 Intel realSense | Depth-camera | Upper limb anatomy
Abstract: Lattice structures have many outstanding properties, and their use in diversified industrial and biomedical fields is widely studied. The advent of additive manufacturing (AM) technologies has further pushed the design of these cellular structures allowing for the fabrication of complex trusses and tailored local geometries. However, geometrical defects introduced by the AM process into printed lattice structures significantly affect their mechanical properties. In this work, the effect of chemical post-processing on the compressive properties of FDM-PLA strut-and-node-based lattice structures is evaluated. A UV resin has been used as a coating film on samples fabricated using Simple Cubic (SC) and Face-Centered Cubic (FCC) unit cells. Results demonstrated a 65% increase in compressive strength for SC unit cells and a 12% increase for FCC unit cells with respect to as-printed samples. Resin coating demonstrated to represent an effective approach to minimize defects of strut-and-node-based lattice structures, thus enhancing mechanical properties.
Keywords: Additive manufacturing | Coating post-process | Compressive properties | Lattice structures
Abstract: This paper reports upon the results of an initial test cycle using a bespoke testing rig designed expressly to examine additively manufactured auxetic components. Firstly, the key problems facing practical researchers in the field of auxetics is explored with the treatment of the boundary condition identified as a key issue. The testing setup that is then introduced utilises a novel method of part mounting and facilitates optical analysis and real-time force measurements. The study analyses three different auxetic structures (re-entrant, chiral, and semi-rigid), a set of samples of which were additively manufactured in TPU material. A range of parameters were varied across the three designs including interior geometry and wall thicknesses in order to demonstrate the effectiveness of the setup for the examination of different structures. Several key results were distilled from the tests that were then further analysed through numerical modelling and discussed with respect to future testing. Our investigation shows a close alignment between the physical testing results and the simulations, indicating that the testing configuration is rigorous and may be used to explore the mechanical behaviour of more complex auxetic componentry.
Keywords: Additive manufacturing | Auxetics | Mechanical analysis | Simulation
Abstract: The digital image correlation (DIC) was used in this paper to obtain full-field measurements of a target vibrating at a frequency higher than the maximum cameras’ frame rate. The down-sampling technique was implemented to compensate for the cameras’ moderate frame rate, thus getting an accurate displacement acquisition even at 6.5 kHz. Two innovative methods to support the DIC application were introduced. The use of fringe projection (or structured light), initially applied on the sample at rest, reduced the effort and time required for the stereo matching task's solution and improved this setting's accuracy and reliability. Additionally, a new time-domain image filtering was proposed and tested to improve the quality of the obtained DIC maps. In combination with the down-sampling, the effect of this filtering technique was tested in this work at (approx.) 2500 and 6500 Hz by measuring the response of a bladed disk to sinusoidal excitation. Evidence of improved results was observed for both frequencies for amplitudes in the range of 10 µm.
Keywords: Bladed disk | Digital image correlation | Down-sampling approach | Low-speed camera | Reverse engineering | Vibration measurement
Abstract: A time-domain filter is presented in this paper for the noise reduction of the camera images, then elaborated for the full-field 3D-DIC vibration analysis of mechanical components. The basic idea behind this filtering is to initially decompose the light signal of each pixel of the raw images, both for the left and the right cameras, with the Fast Fourier Transform (FFT). The signal is then reconstructed with the Inverse FFT by keeping the zero-order harmonic and the first harmonic and just discarding all the others, which only introduce noise contributions. The down-sampling approach is also used in combination with this filtering to reach high loading frequencies, even without (expensive) high-speed cameras, provided that a quite short exposure time is available. A cantilever aluminum plate was tested at 591 Hz, and a similar experiment was repeated on a bladed disk (or blisk) excited at high frequency, 6458 Hz, obtaining clear and smooth displacement maps even in the range of 10 microns. In the blisk application, a single blade with a significantly larger displacement amplitude was clearly observed, which could be interpreted as mistuning evidence.
Abstract: Aims: The aim of the study was to show a case with a midline diastema in a patient with high periodontal risks and gingival recessions treated with clear aligners. The objective was to predict and quantify root movements using a dedicated software that extrapolates data from the Cone Beam Computed Tomography (CBCT). Case Presentation: A 31-year-old female with a mandibular midline diastema asked for an aesthetic treatment. She had vertical bone loss on the lower central incisors, so a CBCT was necessary in order to plan the root movements. The purpose of the treatment was to avoid an uncontrolled tipping of the incisors and, therefore, a vestibular movement of the roots, which could cause serious periodontal problems. Conclusion: At the end of the treatment, the complete closure of the diastema and the radiographic healing of the vertical bone loss between mandibular central incisors were achieved. The superimpositions with the virtual setup demonstrated predictability of root movements of 76%.
Keywords: Clear aligners | Cone beam computed tomography | Midline diastema | Periodontal conditions | Periodontal disease | Virtual root setup
Abstract: The potential of additive manufacturing to produce optimised and customized polymeric parts is often impaired by poor surface finish, low mechanical properties, and insufficient dimensional accuracy. Post-processing treatments are usually adopted to address these issues. Scientific community and industrial actors are engaged in the development and use of post-processing to enhance the performance and widen the range of application of polymeric components manufactured by additive technologies. The present work aims to provide an exhaustive classification and discussion of the post-processing treatments, as well as an extensive literature review of the approaches proposed within the scientific community. A holistic view of post-processing is provided, including a discussion of the benefits associated with each technique as well as its side effects. This work is intended to support the selection of the most appropriate post-processing by considering multiple aspects such as the material, part geometry, processing time, costs, and treatment specificity.
Keywords: Additive manufacturing | polymers | post-processing treatments
Abstract: 3D digital models of the upper limb anatomy represent the starting point for the design process of bespoke devices, such as orthoses and prostheses, which can be modeled on the actual patient’s anatomy by using CAD (Computer Aided Design) tools. The ongoing research on optical scanning methodologies has allowed the development of technologies that allow the surface reconstruction of the upper limb anatomy through procedures characterized by minimum discomfort for the patient. However, the 3D optical scanning of upper limbs is a complex task that requires solving problematic aspects, such as the difficulty of keeping the hand in a stable position and the presence of artefacts due to involuntary movements. Scientific literature, indeed, investigated different approaches in this regard by either integrating commercial devices, to create customized sensor architectures, or by developing innovative 3D acquisition techniques. The present work is aimed at presenting an overview of the state of the art of optical technologies and sensor architectures for the surface acquisition of upper limb anatomies. The review analyzes the working principles at the basis of existing devices and proposes a categorization of the approaches based on handling, pre/post-processing effort, and potentialities in real-time scanning. An in-depth analysis of strengths and weaknesses of the approaches proposed by the research community is also provided to give valuable support in selecting the most appropriate solution for the specific application to be addressed.
Keywords: Body scanner | Depth cameras | Handheld scanner | Stationary scanner | Structured light scanning | Upper limb 3D scanning
Abstract: The use of metal-free thermoplastic materials plays a key role in the orthodontic digital workflow due to the increasing demand for clear aligner treatments. Three thermoplastic polymers commonly used to fabricate clear aligners, namely Duran®, Biolon® and Zendura®, were investigated to evaluate the effect of thermoforming (T.), storage in artificial saliva (S.A.S.) and their combination on their mechanical properties. Elastic modulus and yield stress of the specimens were characterized. Each material was characterized for each condition through tensile tests (ISO527-1). The results showed that thermoforming does not lead to a significant decrease in yield stress, except for Zendura® that showed about a 30% decrease. An increase of the elastic modulus of Duran® and Zendura®, instead, was observed after thermoforming. The same increase was noticed for the yield stress of Duran®. For S.A.S. specimens, the elastic modulus generally decreases compared to supplier condition (A.S.) and simply thermoformed material. A decrease of yield stress, instead, is significant for Zendura®. The results demonstrated that the impact of the operating conditions on the mechanical properties can vary according to the specific polymer. To design reliable and effective orthodontic treatments, the materials should be selected after their mechanical properties are characterized in the simulated intraoral environment.
Keywords: Mechanical properties | Orthodontic aligners | Simulated oral environment | Thermoplastic polymers
Abstract: The use of light encoding techniques is widespread in the field of 3D surface reconstruction. This paper presents a stereo-camera calibration methodology, which integrates structured light encoding with an active digital device. The structured light encoding approach is proposed to unambiguously solve the stereo matching issue for stereo-camera setups. A sequence of vertical and horizontal binary striped patterns, combined with a checkerboard pattern, is displayed by a high-resolution LCD screen, which is used as calibration board. A bundle adjustment technique is adopted to simultaneously adjust both camera parameters and screen geometry, as part of the stereo-camera calibration process, thus taking into account the possible inaccuracies of the digital display. The same structured light approach, with small variants, is projected by a multimedia digital projector to carry out 3D surface reconstruction. The proposed methodology defines a comprehensive framework for the development of a 3D optical scanner, from calibration to 3D acquisition, which has been validated by measuring primitive surfaces and reconstructing free-form shapes with different stereo-camera setups.
Keywords: Binary-code | LCD screen | Stereo-camera calibration | Stripe shifting | Structured light encoding
Abstract: Moisture absorption degrades the mechanical properties of polymeric parts that are 3D-printed by fused filament fabrication (FFF). This limitation is particularly significant for short fiber-reinforced polymers because the mechanical enhancement obtained by the fiber reinforcement can be compromised by the plasticizing effect introduced by water absorption. Therefore, the present work investigates the effects of two different coatings, a UV cured acrylate resin and an acrylic varnish, on the moisture absorption of FFF 3D-printed samples consisting of polyamide reinforced by short carbon fibers. Water content (CI) and open porosity (OP) were estimated through water absorption tests in distilled water for 2, 24, and 168 h, and after reconditioning. The coating effects were evaluated by conducting tensile tests to compare the Young's modulus, yield stress, and ultimate stress of the coated and uncoated specimens. The results demonstrated a significant reduction of CI and OP with both the acrylic and UV resin coatings, as well as considerable enhancements of these samples’ mechanical properties. Stress-strain curves evidenced a strain reduction after water immersion, which can be ascribed to a greater stability against different moisture conditions. These findings indicate the significant potential of the proposed coating processes to extend the use of FFF 3D-printed composite materials to a broader range of applications.
Keywords: Fused filament fabrication | Material extrusion | Mechanical properties enhancement | Moisture absorption | Short fiber-reinforced polymers
Abstract: Dynamic characterization of vibrating targets represents a critical issue for many industrial fields. In this paper, a stereo-camera system integrated with a Digital Image Correlation (DIC) algorithm is proposed with the aim at performing 3D full-field vibration measurements in the range of kHz. The system exploits two industrial low-speed cameras, and the Nyquist-Shannon frequency limitation is overcome by a down-sampling approach under the hypothesis that the vibration signal is characterized by a single known frequency component. Experimental results obtained from the measurement of vibrational responses of a cantilever plate excited at three high-frequency resonance values (1121 Hz, 2956 Hz and 4010 Hz) are provided. A comparison with numerical analyses evidences the effectiveness of the proposed approach.
Keywords: Digital Image Correlation | Low-frame-rate cameras | Stereo-camera setup | Vibration measurement
Abstract: In recent years, Fused Deposition Modelling (FDM) has become one of the most attractive Additive Manufacturing (AM) techniques, due to the advantages in the production of complex shapes with a wide range of materials and low investment costs. The thermoplastic polymers used for FDM technology are characterized by low mechanical properties if compared to those of composites and metals. This issue is usually overcome by reinforcing the thermoplastic polymer with chopped fibres or particles. Moreover, a second issue arises, which is represented by the water absorption with a relevant impact on mechanical properties and dimensional stability of printed models. In this paper, an experimental study is presented with the aim at evaluating the water absorption influence on mechanical properties of Carbon PA (Polyamide matrix reinforced with Carbon Fiber at 20%) specimens fabricated with the FDM technique. Two post-processing treatments, based on the use of acrylic spray and photosensitive resin, have been also proposed to improve the behaviour of Carbon PA printed parts. Results of water absorption tests and tensile tests demonstrated a significant improvement in terms of weight stability and mechanical properties by adopting the proposed post-processing treatments.
Keywords: Carbon fiber | Coating treatment | Fused Deposition Modeling | Mechanical characterization | Water absorption
Abstract: Background: Clear aligners (CA) are among the most chosen orthodontic therapies for patients who require an invisible treatment. Previous studies showed that the thermoforming process and the complexity of the intraoral environment might alter the properties of these devices. The aim of the current prospective clinical study was to assess the thickness changes of the CA after 10 days of intraoral use. The secondary aim was to assess the reproducibility of the thermoforming process, in terms of aligner thickness. Materials and methods: CA from 18 consecutive patients (13 women, 5 men, mean age 28.8 ± 9.6 years) were investigated. Before intraoral exposure (T0), the thickness of the unused CA was measured at different occlusal points on a 3D model with a dedicated software (Geomagic Qualify 2013; 3D Systems, Rock Hill, SC, USA). Two CA configurations were studied: passive maxillary aligner (P—no tooth movement; no shape for attachments) and active maxillary aligner (A—tooth movement; shape for attachments and divot). The used aligners were returned after 10 days (T1) and the thickness measurements were repeated. A Student’s t test for paired data (T1 vs. T0) was applied to compare the thicknesses of used and unused devices (significance level after Bonferroni correction for multiple comparison was set at p < 0.0014). Furthermore, to study the reproducibility of the thermoforming process, P and A aligners were thermoformed twice, and the thicknesses of the two unused thermoformed devices were compared by means of Student’s t test for paired data (significance level after Bonferroni correction for multiple comparison was set at p < 0.0014) and Dahlberg’s error. Results: The thermoforming process showed good reproducibility for both aligner configurations, with a maximum Dahlberg’s error of 0.13 mm. After intraoral use, the thickness of P showed some statistically significant, but not clinically relevant, thickness changes as compared to the unused aligners, while A did not show any significant changes. Conclusion: Considering the thickness changes, the thermoforming process is reliable both with active and passive aligner configurations. Also, the CA examined show good thickness stability after physiological intraoral ageing in a population of healthy adults.
Keywords: Adult | Aesthetic | Clear aligners | Dimensional stability | Intraoral ageing | Mechanical proprieties | Orthodontic appliance | Thermoforming | Thermoplastic
Abstract: A single-camera stereo-digital image correlation (stereo-DIC) system to obtain 3D full-field vibration measurements is proposed. The optical setup is composed of two planar mirrors and a single low frame rate camera, thus resulting in a compact and low-cost equipment. The two mirrors are used to create pseudo-stereo images of a target surface on the camera sensor, which are then correlated by using stereo-DIC. The image acquisition process is carried out at low frame rates and the Nyquist-Shannon frequency limitation is overcome by adopting a down-sampling approach under the hypothesis that the vibration signal is characterized by a single known frequency component. The developed pseudo-stereo DIC system allows to obtain 3D full-field vibration measurements in a frequency range up to 4 kHz even with an available frame rate (at full resolution) of 178 fps. The effectiveness of the described approach has been verified by performing vibration measurements on a cantilever plate and a turbine blade.
Keywords: Digital image correlation | Down-sampling approach | Single low-speed camera | Vibration measurement
Abstract: Recent advances in Additive Manufacturing (AM) technologies have allowed a widespread diffusion of their use in different fields. 3D printing is becoming commonplace for biomedical applications requiring the custom fabrication of prostheses and appliances fitting patient-specific anatomies. In this work, the feasibility of a vat photopolymerization technology, based on Digital Light Processing (DLP), has been investigated for the manufacturing of polymeric orthodontic appliances. A custom DLP 3D printer has been developed by exploiting an off-the-shelf digital projector, with the aim at studying the influence of printing parameters on the surface roughness. The feasibility of using Dental LT Clear resin, a biocompatible photopolymer specifically designed for SLA technology, has been finally verified.
Keywords: Additive manufacturing | Custom DLP 3D printer | Orthodontic appliances
Abstract: Camera calibration plays a fundamental role for 3D computer vision since it is the first step to recover reliable metric information from 2D images. The calibration of a stereo-vision system is a two-step process: firstly, the calibration of the individual cameras must be carried out, then the two individual calibrations are combined to retrieve the relative placement between the two cameras, and to refine intrinsic and extrinsic parameters. The most commonly adopted calibration methodology uses multiple images of a physical checkerboard pattern. However, the process is time-consuming since the operator must move the calibration target into different positions, typically from 15 to 20. Moreover, the calibration of different optical setups requires the use of calibration boards, which differ for size and number of target points depending on the desired working volume. This paper proposes an innovative approach to the calibration, which is based on the use of a conventional computer screen to actively display the calibration checkerboard. The potential non-planarity of the screen is compensated by an iterative approach, which also estimate the actual screen shape during the calibration process. The use of an active display greatly enhances the flexibility of the stereo-camera calibration process since the same device can be used to calibrate different optical setups by simply varying number and size of the displayed squared patterns.
Keywords: Active display | Reverse Engineering | Stereo camera calibration | Structured light scanner
Abstract: Objectives: To investigate the in vitro cytotoxicity of different thermoplastic materials for clear aligners on human primary gingival fibroblasts (HGFs). Materials and Methods: Four materials for clear aligners were considered in this study: Duran (Scheu-Dental GmbH, Iserlohn, Germany), Biolon (Dreve Dentamid GmbH, Unna, Germany), Zendura (Bay Materials LLC, Fremont, CA, USA), and SmartTrack (Align Technology, San Jose, CA, USA). Three out of four materials (Duran, Biolon, Zendura) were assessed as thermoformed and nonthermoformed, whereas the SmartTrack was assessed only as thermoformed. The samples were placed at 378C in airtight test tubes containing Dulbecco’s Modified Eagle’s Medium (DMEM; 0.1 mg/mL) for 14 days. The cell viability of HGFs cultured with this medium was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Data were analyzed by means of one-way and two-way analysis of variance and post hoc tests (a ¼ 0.05). Results: Each material exhibited a slight cytotoxic effect after 14 days. The highest cytotoxicity level on HGFs was achieved by Biolon (64.6% 6 3.3 of cell viability), followed by Zendura (74.4% 6 2.3 of cell viability), SmartTrack (78.8% 6 6.3 of cell viability), and finally Duran (84.6% 6 4 of cell viability), which was the least cytotoxic. In the comparison between nonthermoformed and thermoformed materials for Duran, Biolon, and Zendura, the thermoformed materials showed the highest level of cytotoxicity (P, .001). Conclusions: Under the experimental conditions of this study, all the materials for clear aligners presented a slight cytotoxicity. Biolon was the most cytotoxic and the thermoforming process increased the cytotoxicity of the materials.
Keywords: Biocompatibility | Clear aligners | Cytotoxicity | Orthodontics
Abstract: Aim. To evaluate the biomechanical effects of four different auxiliary-aligner combinations for the extrusion of a maxillary central incisor and to define the most effective design through finite element analysis (FEA). Materials and Methods. A full maxillary arch (14 teeth) was modelled by combining two different imaging techniques: cone beam computed tomography and surface-structured light scan. The appliance and auxiliary element geometries were created by exploiting computer-aided design (CAD) procedures. The reconstructed digital models were imported within the finite element solver (Ansys® 17). For the extrusion movement, the authors compared the aligner without an attachment with three auxiliary-aligner designs: a rectangular palatal attachment, a rectangular buccal attachment, and an ellipsoid buccal attachment. The resulting force-moment (MF) system delivered by the aligner to the target tooth and the tooth displacement were calculated for each scenario. Results. The maximum tooth displacement along the z-axis (0.07 mm) was obtained with the rectangular palatal attachment, while the minimum (0.02 mm) was obtained without any attachments. With the ellipsoid attachment, the highest undesired moments Mx and My were found. The rectangular palatal attachment showed the highest Fz (2.0 N) with the lowest undesired forces (Fx = 0.4 N; Fy = -0.2 N). Conclusions. FEA demonstrated that the rectangular palatal attachment can improve the effectiveness of the appliance for the extrusion of an upper central incisor.
Abstract: The use of composite materials allows to have a great flexibility in terms of mechanical and physical characteristics. One of the most used composite structure in naval field, is the sandwich, which is composed by a stacking sequence of different plies. The designer, in preliminary phase, must handle a great quantity of degree of freedom (types of materials, orientation of the fibres, position along the stack, thickness, etc.) in order to reach the best compromise between mechanical behaviour, environmental impacts and production costs. Finite Element analysis represents a useful tool in order to optimize all these parameters and to estimate the outcome of experimental tests at design stage. The main goal of this work is to develop and to validate a FE model for the simulation of a particular family of composites, widely used in naval field and, in particular, in High Speed Crafts and powerboats. The first part of the paper concerns the experimental tests on two different types of sandwich specimens. Two families of tests were conducted: four-point bending tests and impact drop tests. The second part of the paper focuses on the validation of a FE model for both experimental setups.
Keywords: Finite Element | Impact tests | Lightweight composites | Offshore powerboats | Sandwich composites
Abstract: Despite the existence of a wide variety of standards to create hand-made illustrations of lithic artefacts, the conventional process is laborious, time-consuming and the quality of the drawings is highly variable. In this paper, a novel computer-based methodology to create automatic technical documentation of lithic artefacts, in the form of manual-like drawings, is presented. The method exploits the artefact digital model obtained by a 3D optical scanner. An optimization process is proposed to orient the digital model reproducing the conventional positioning. A lighting model is used to introduce an illumination source having different directions, to highlight surface details. A set of images is then created and segmented to retrieve the artefact outline and the internal ridges between flake scars. Potentialities of the proposed methodology are illustrated by analyzing three different stone artefacts acquired by a structured light scanner. 2D technological drawings are automatically created and compared to those obtained by an experienced lithic illustrator.
Keywords: 3D scanning | Automatic technical drawing | Lithic artefact | Reverse engineering
Abstract: The present paper describes the development and characterization of a structured light stereo catadioptric scanner for the omnidirectional reconstruction of internal surfaces. The proposed approach integrates two digital cameras, a multimedia projector and a spherical mirror, which is used to project the structured light patterns generated by the light emitter and, at the same time, to reflect into the cameras the modulated fringe patterns diffused from the target surface. The adopted optical setup defines a non-central catadioptric system, thus relaxing any geometrical constraint in the relative placement between optical devices. An analytical solution for the reflection on a spherical surface is proposed with the aim at modelling forward and backward projection tasks for a non-central catadioptric setup. The feasibility of the proposed active catadioptric scanner has been verified by reconstructing various target surfaces. Results demonstrated a great influence of the target surface distance from the mirror's centre on the measurement accuracy. The adopted optical configuration allows the definition of a metrological 3D scanner for surfaces disposed within 120 mm from the mirror centre.
Keywords: Catadioptric system | Reverse engineering | Spherical mirror | Structured light stereo system
Abstract: The manual drafting of lithics artefacts could be a very time-consuming work, and it could be cumbersome on the archaeological site. In this case, a 3D digital model of the object could be very useful. Nowadays, several digitizing technologies are available to easily acquire information about the shape of an object. Virtual models could be used to create a digital museum or to share information between researchers. On the other hand, the manual drafting of a lithic object contains information about the technologies used to realize it. Information about the core setup, types of chipping surfaces, detach sequence of supports, and much more. In this work a method to easily obtain a hand-made-like draft of lithic artefacts is proposed. The method is based on the 3D acquisition of the object with a structured-light based scanner and a sequence of digital processing of the acquired data.
Abstract: The combination of mirrors and lenses, which defines a catadioptric sensor, is widely used in the computer vision field. The definition of a catadioptric sensors is based on three main features: hardware setup, projection modelling and calibration process. In this paper, a complete description of these aspects is given for an omnidirectional sensor based on a spherical mirror. The projection model of a catadioptric system can be described by the forward projection task (FP, from 3D scene point to 2D pixel coordinates) and backward projection task (BP, from 2D coordinates to 3D direction of the incident light). The forward projection of non-central catadioptric vision systems, typically obtained by using curved mirrors, is usually modelled by using a central approximation and/or by adopting iterative approaches. In this paper, an analytical closed-form solution to compute both forward and backward projection for a non-central catadioptric system with a spherical mirror is presented. In particular, the forward projection is reduced to a 4th order polynomial by determining the reflection point on the mirror surface through the intersection between a sphere and an ellipse. A matrix format of the implemented models, suitable for fast point clouds handling, is also described. A robust calibration procedure is also proposed and applied to calibrate a catadioptric sensor by determining the mirror radius and center with respect to the camera.
Keywords: Backward projection model | Catadioptric sensor | Computer vision | Forward projection model | Spherical mirror
Abstract: Microfluidic systems demonstrated to improve the analysis of biological and chemical processes by providing a more controlled fluid-handling environment. Typically, microfluidic systems are created in monolithic form by means of microfabrication techniques that constrain designers to work in a two-dimensional space. In this regard, Additive Manufacturing (AM) is a powerful set of technologies that can deal with the complexity of 3D structures producing flow paths with sections differing in size and direction. In this work, the use of a commercial laser-based stereolithography 3D printer has been firstly explored to fabricate transparent channels for flow reactors. A custom 3D printer, based on Digital Light Processing Stereolithography (DLP-SLA), has then been developed with the aim at gaining flexibility and overcoming typical limitations raised from standard commercial solutions. The effectiveness of the developed DLP-SLA 3D printer has been experienced by printing transparent fluidic devices with embedded channels with a specifically designed three-step printing process.
Keywords: Additive manufacturing | DLP 3D printing | fluidic reactor | laser-based stereolithograpy
Abstract: A 3D full-field optical system for high frequency vibration measurement is proposed. The system is composed of a single low-frame-rate camera and two planar mirrors. This compact optical setup overcomes the typical drawback of capturing synchronous acquisitions in the case of a camera pair. Moreover, planar mirrors allow for the use of the classical pinhole model and, thus, conventional stereo-calibration techniques. The use of a low-frame-rate camera provides on the one hand a high-resolution sensor with a relatively low-cost hardware but imposes, on the other, the adoption of a down-sampling approach, which is applicable only when a single (known) sinusoidal load is applied to the structure. The effectiveness of the proposed setup has been verified by the 3D vibration measurement of two different targets up to a frequency of 1 kHz, corresponding to a displacement amplitude of 0.01 mm.
Keywords: digital image correlation | down-sampling approach | Reverse engineering | single low-speed camera
Abstract: 3D virtual reconstruction of human body parts is nowadays a common practice in many research fields such as the medical one, the manufacturing of customized products or the creation of personal avatar for gaming purpose. The acquisition can be performed with the use of an active stereo system (i.e., laser scanner, structured light sensors) or with the use of a passive image-based approach. While the former represents a consolidated approach in human modeling, the second is still an active research field. Usually, the reconstruction of a body part through a scanning system is expensive and requests to project light on the patient’s body. On the other hand, the image-based approach could use multi-photo technique to reconstruct a real scene and provides some advantages: low equipment costs (only one camera) and rapid acquisition process of the photo set. In this work, the use of the photogrammetry approach for the reconstruction of humans’ face has been investigated as an alternative to active scanning systems. Two different photogrammetric approaches have been tested to verify their potentiality and their sensitivity to configuration parameters. An initial comparison among them has been performed, considering the overall number of points detected (sparse point cloud reconstruction, dense point cloud reconstruction). Besides, to evaluate the accuracy of the reconstruction, a set of measures used in the design of wearable head-related products has been assessed.
Abstract: In the computer vision field, the reconstruction of target surfaces is usually achieved by using 3D optical scanners assembled integrating digital cameras and light emitters. However, these solutions are limited by the low field of view, which requires multiple acquisition from different views to reconstruct complex free-form geometries. The combination of mirrors and lenses (catadioptric systems) can be adopted to overcome this issue. In this work, a stereo catadioptric optical scanner has been developed by assembling two digital cameras, a spherical mirror and a multimedia white light projector. The adopted configuration defines a non-single viewpoint system, thus a non-central catadioptric camera model has been developed. An analytical solution to compute the projection of a scene point onto the image plane (forward projection) and vice-versa (backward projection) is presented. The proposed optical setup allows omnidirectional stereo vision thus allowing the reconstruction of target surfaces with a single acquisition. Preliminary results, obtained measuring a hollow specimen, demonstrated the effectiveness of the described approach.
Keywords: 3D acquisition | catadioptric stereo vision system | internal geometries acquisition | spherical mirror projection model | structured light scanning
Abstract: Orthodontic treatments are usually performed using fixed brackets or removable oral appliances, which are traditionally made from alginate impressions and wax registrations. Among removable devices, eruption guidance appliances are used for early orthodontic treatments in order to intercept and prevent malocclusion problems. Commercially available eruption guidance appliances, however, are symmetric devices produced using a few standard sizes. For this reason, they are not able to meet all the specific patient’s needs since the actual dental anatomies present various geometries and asymmetric conditions. In this article, a computer-aided design-based methodology for the design and manufacturing of a patient-specific eruption guidance appliances is presented. The proposed approach is based on the digitalization of several steps of the overall process: from the digital reconstruction of patients’ anatomies to the manufacturing of customized appliances. A finite element model has been developed to evaluate the temporomandibular joint disks stress level caused by using symmetric eruption guidance appliances with different teeth misalignment conditions. The developed model can then be used to guide the design of a patient-specific appliance with the aim at reducing the patient discomfort. At this purpose, two different customization levels are proposed in order to face both arches and single tooth misalignment issues. A low-cost manufacturing process, based on an additive manufacturing technique, is finally presented and discussed.
Keywords: additive manufacturing | eruption guidance appliance | finite element model | Orthodontics | temporomandibular joint
Abstract: Different sensor technologies are available for dimensional metrology and reverse engineering processes. Tactile systems, optical sensors, and computed tomography (CT) are being used to an increasing extent in various industrial contexts. However, each technique has its own peculiarities, which may limit its usability in demanding applications. The measurement of complex shapes, such as those including hidden and twisted geometries, could be better afforded by multisensor systems combining the advantages of two or more data acquisition technologies. In this paper, a fully automatic multisensor methodology has been developed with the aim at performing accurate and reliable measurements of both external and internal geometries of industrial components. The methodology is based on tracking a customized hand-held tactile probe by a passive stereo vision system. The imaging system automatically tracks the probe by means of photogrammetric measurements of markers distributed over a plate rigidly assembled to the tactile frame. Moreover, the passive stereo system is activated with a structured light projector in order to provide full-field scanning data, which integrate the point-by-point measurements. The use of the same stereo vision system for both tactile probe tracking and structured light scanning allows the two different sensors to express measurement data in the same reference system, thus preventing inaccuracies due to misalignment errors occurring in the registration phase. The tactile methodology has been validated by measuring primitive shapes. Moreover, the effectiveness of the integration between tactile probing and optical scanning has been experienced by reconstructing twisted and internal shapes of industrial impellers.
Keywords: industrial impeller | multisensor system | structured light scanning | tactile-optical measuring system
Abstract: Transparent and removable aligners represent an effective solution to correct various orthodontic malocclusions through minimally invasive procedures. An aligner-based treatment requires patients to sequentially wear dentition-mating shells obtained by thermoforming polymeric disks on reference dental models. An aligner is shaped introducing a geometrical mismatch with respect to the actual tooth positions to induce a loading system, which moves the target teeth toward the correct positions. The common practice is based on selecting the aligner features (material, thickness, and auxiliary elements) by only considering clinician's subjective assessments. In this article, a computational design and engineering methodology has been developed to reconstruct anatomical tissues, to model parametric aligner shapes, to simulate orthodontic movements, and to enhance the aligner design. The proposed approach integrates computer-aided technologies, from tomographic imaging to optical scanning, from parametric modeling to finite element analyses, within a 3-dimensional digital framework. The anatomical modeling provides anatomies, including teeth (roots and crowns), jaw bones, and periodontal ligaments, which are the references for the down streaming parametric aligner shaping. The biomechanical interactions between anatomical models and aligner geometries are virtually reproduced using a finite element analysis software. The methodology allows numerical simulations of patient-specific conditions and the comparative analyses of different aligner configurations. In this article, the digital framework has been used to study the influence of various auxiliary elements on the loading system delivered to a maxillary and a mandibular central incisor during an orthodontic tipping movement. Numerical simulations have shown a high dependency of the orthodontic tooth movement on the auxiliary element configuration, which should then be accurately selected to maximize the aligner's effectiveness.
Keywords: Computational engineering | Computer-aided design | Finite element analysis | Orthodontic treatment | Patient-specific modeling | Polymeric aligner
Abstract: The dynamic characterization of mechanical components is a crucial issue in industry, especially in the field of rotating machinery. High frequency loads are typical in this field and experimental tools need to fulfill severe specifications to be able to analyze these high-speed phenomena. In this work, an experimental setup, based on a Digital Image Correlation (DIC) technique with a projected speckle pattern, is presented. The proposed approach allows the measurement of vibrational response characterized by a single sinusoidal component having a frequency up to 500 Hz and an amplitude lower than 10 μm.
Keywords: Geometrical inspection | Optiocal touch probe | Reverse Engineering
Abstract: Mechanical components are often subjected to tolerances and geometrical specification. This paper describes an automatic 3D measurement system based on the integration of a stereo structured light scanner and a tactile probe. The tactile probe is optically tracked by the optical scanner by means of 3D measurements of a prismatic flag, rigidly connected to the probe and equipped with multiple chessboard patterns. Both the stereo vision system and the tactile probe can be easily configured enabling complete reconstructions of components having complex shapes. For instance, structured light scanning can be used to acquire external and visible geometries while tactile probing can be limited to the acquisition of internal and hidden surfaces.
Keywords: Geometrical inspection | Optical touch probe | Reverse Engineering
Abstract: Clear thermoplastic aligners are nowadays widely used in orthodontics for the correction of malocclusion or teeth misalignment defects. The treatment is virtually designed with a planning software that allows for a definition of a sequence of little movement steps from the initial tooth position to the final desired one. Every single step is transformed into a physical device, the aligner, by the use of a 3D printed model on which a thin foil of plastic material is thermoformed. Manufactured aligners could have inherent limitations such as dimensional instability, low strength, and poor wear resistance. These issues could be associated with material characteristics and/or with the manufacturing processes. The present work aims at the characterization of the manufactured orthodontic devices. Firstly, mechanical properties of different materials have been assessed through a set of tensile tests under different experimental conditions. The tests have the purpose of analyzing the effect that the forming process a d the normal use of the aligner may have on mechanical properties of the material. The manufacturing process could also introduce unexpected limitations in the resulting aligners. This would be a critical element to control in order to establish resulting forces on teeth. Several studies show that resulting forces could be greatly influenced by the aligner thickness. A method to easily measure the actual thickness of the manufactured aligner is proposed. The analysis of a number of real cases shows as the thickness is far to be uniform and could vary strongly along the surface of the tooth.
Keywords: 3D Human Modeling | Clear Aligner | Mechanical Properties Assessment | Optical 3D Scanner | Thermoforming Process | Virtual Design
Abstract: Orthodontic treatments based on removable thermoplastic aligners are becoming quite common in clinical practice. However, there is no technical literature explaining how the loads are transferred from the thermoformed aligner to the patient dentition. Moreover, the role of auxiliary elements used in combination with the aligner, such as attachments and divots, still needs to be thoroughly explained. This paper is focused on the development of a Finite Element (FE) model to be used in the design process of shape attributes of orthodontic aligners. Geometrical models of a maxillary dental arch, including crown and root shapes, were created by combining optical scanning and Cone Beam Computed Tomography (CBCT). Finite Element Analysis (FEA) was used to compare five different aligner’s configurations for the same tooth orthodontic tipping movement (rotation around the tooth’s center of resistance). The different scenarios were analyzed by comparing the moment along the mesio-distal direction of the tooth and the resulting moment-to-force ratio (M:F) delivered to the tooth on the plane of interest. Results evidenced the influence of the aligner’s configuration on the effectiveness of the planned orthodontic movement.
Keywords: Anatomical modelling | Numerical analysis | Orthodontic aligner | Orthodontic tooth movement
Abstract: In the present work, the effect of Eruption Guidance Appliances (EGAs) on TemporoMandibular Joint (TMJ) disks stress level is studied. EGAs are orthodontic appliances used for early orthodontic treatments in order to prevent malocclusion problems. Commercially available EGAs are usually produced by using standard sizes. For this reason, they are not able to meet all the specific needs of each patient. In particular, EGAs are symmetric devices, while patient arches generally present asymmetric conditions. Thus, uneven stress levels may occur in TMJ disks, causing comfort reduction and potential damage to the most solicited disk. On the other hand, a customized EGA could overcome these issues, improving the treatment effectiveness. In this preliminary study, a Finite Element (FE) model was developed to investigate the effects of a symmetric EGA when applied to an asymmetric mouth. Different misalignment conditions were studied to compare the TMJ disks stress levels and to analyze the limitations of a symmetric EGA. The developed FE model can be used to design patient-specific EGAs, which could be manufactured by exploiting non-conventional techniques such as 3D printing.
Keywords: Eruption guidance appliance (EGA) | FE model | Patient-specific orthodontic appliance | TMJ disks stress | TMJ disorders
Abstract: In the last decade, orthodontic removable thermoplastic aligners have become a common alternative to conventional fixed brackets and wires. However, the wide spread of this typology of orthodontic treatment was not followed by an adequate scientific investigation about its biomechanical effects onto the teeth. In the present work, a patient-specific framework has been developed with the aim of simulating orthodontic tooth movements by using plastic aligners. A maxillary and a mandibular dental arch were reconstructed by combining optical and radiographic imaging methods. A Finite Element (FE) model was then created to analyze two different aligner configurations. In particular, the effect of a non-uniform aligner’s thickness and of a customized initial offset between the aligner and the patient dentition were studied. The force-moment systems delivered by the aligner to a mandibular central incisor during labiolingual tipping, and to a maxillary central incisor during rotation were analyzed and discussed.
Keywords: Aligner thickness | Customized aligner shape | Finite element model | Orthodontic aligner design
Abstract: Abstract: In the field of orthodontics, the use of Removable Thermoplastic Appliances (RTAs) to treat moderate malocclusion problems is progressively replacing traditional fixed brackets. Generally, these orthodontic devices are designed on the basis of individual anatomies and customised requirements. However, many elements may affect the effectiveness of a RTA-based therapy: accuracies of anatomical reference models, clinical treatment strategies, shape features and mechanical properties of the appliances. In this paper, a numerical model for customised orthodontic treatments planning is proposed by means of the finite element method. The model integrates individual patient’s teeth, periodontal ligaments, bone tissue with structural and geometrical attributes of the appliances. The anatomical tissues are reconstructed by a multi-modality imaging technique, which combines 3D data obtained by an optical scanner (visible tissues) and a computerised tomography system (internal tissues). The mechanical interactions between anatomical shapes and appliance models are simulated through finite element analyses. The numerical approach allows a dental technician to predict how the RTA attributes affect tooth movements. In this work, treatments considering rotation movements for a maxillary incisor and a maxillary canine have been analysed by using multi-tooth models. Graphical Abstract: [Figure not available: see fulltext.]
Keywords: Anatomical modelling | Numerical analysis | Orthodontic tooth movement | Removable thermoplastic appliance
Abstract: Introduction Moment-to-force ratios (M:F) define the type of tooth movement. Typically, the relationship between M:F and tooth movement has been analyzed in a single plane. Here, to improve the 3-dimensional tooth movement theory, we tested the hypothesis that the mathematical relationships between M:F and tooth movement are distinct, depending on force system directions. Methods A finite element model of a maxillary first premolar, scaled to average tooth dimensions, was constructed based on a cone-beam computed tomography scan. We conducted finite element analyses of the M:F and tooth movement relationships, represented by the projected axis of rotation in each plane, for 510 different loads. Results We confirmed that a hyperbolic equation relates the distance and M:F; however, the constant of proportionality ("k") varied nonlinearly with the force direction. With a force applied parallel to the tooth's long axis, "k" was 12 times higher than with a force parallel to the mesiodistal direction and 7 times higher than with a force parallel to the buccolingual direction. Conclusions The M:F influence on tooth movement depends on load directions. It is an incomplete parameter to describe the quality of an orthodontic load system if it is not associated with force and moment directions.
Abstract: Dedicated imaging methods are among the most important tools of modern computer-aided medical applications. In the last few years, cone beam computed tomography (CBCT) has gained popularity in digital dentistry for 3D imaging of jawbones and teeth. However, the anatomy of a maxillofacial region complicates the assessment of tooth geometry and anatomical location when using standard orthogonal views of the CT data set. In particular, a tooth is defined by a sub-region, which cannot be easily separated from surrounding tissues by only considering pixel grey-intensity values. For this reason, an image enhancement is usually necessary in order to properly segment tooth geometries. In this paper, an anatomy-driven methodology to reconstruct individual 3D tooth anatomies by processing CBCT data is presented. The main concept is to generate a small set of multi-planar reformation images along significant views for each target tooth, driven by the individual anatomical geometry of a specific patient. The reformation images greatly enhance the clearness of the target tooth contours. A set of meaningful 2D tooth contours is extracted and used to automatically model the overall 3D tooth shape through a B-spline representation. The effectiveness of the methodology has been verified by comparing some anatomy-driven reconstructions of anterior and premolar teeth with those obtained by using standard tooth segmentation tools.
Keywords: 3D imaging | B-spline modelling | Cone beam computed tomography | Digital dentistry | Tooth segmentation
Abstract: In the field of oral rehabilitation, the combined use of 3D imaging technologies and computer-guided approaches allows the development of reliable tools to be used in preoperative assessment of implant placement. In particular, the accurate transfer of the virtual planning into the operative field through surgical guides represents the main challenge of modern dental implantology. Guided implant positioning allows surgical and prosthetic approaches with minimal trauma by reducing treatment time and decreasing patient’s discomfort. This paper aims at defining a CAD/CAM framework for the accurate planning of flapless dental implant surgery. The system embraces three major applications: (1) freeform modelling, including 3D tissue reconstruction and 2D/3D anatomy visualization, (2) computer-aided surgical planning and customised template modelling, (3) additive manufacturing of guided surgery template. The tissue modelling approach is based on the integration of two maxillofacial imaging techniques: tomographic scanning and surface optical scanning. A 3D virtual maxillofacial model is created by matching radiographic data, captured by a CBCT scanner, and surface anatomical data, acquired by a structured light scanner. The pre-surgical planning process is carried out and controlled within the CAD application by referring to the integrated anatomical model. A surgical guide is then created by solid modelling and manufactured by additive techniques. Two different clinical cases have been approached by inserting 11 different implants. CAD-based planned fixture placements have been transferred into the clinical field by customised surgical guides, made of a biocompatible resin and equipped with drilling sleeves.
Keywords: Additive manufacturing | Biomedical imaging | Computer-assisted dental implantology | Freeform solid modelling | Oral rehabilitation
Abstract: In recent years, the public demand of less invasive orthodontic treatments has led to the development of appliances that are smaller, lower profile and more transparent with respect to conventional brackets and wires. Among aesthetic appliances, removable thermoplastic aligners gained instant appeal to patients since able to perform comprehensive orthodontic treatments without sacrificing comfort issues. The aligner must deliver an appropriate force in order to move the tooth into the expected position. However, at present, the relationship between applied force and aligner properties (i.e., aligner's thickness) is poorly understood. In this paper, a patient-specific framework has been developed to simulate orthodontic tooth movements by using aligners. In particular, a finite element model has been created in order to optimise the aligner's thickness with regard to the magnitude of the force-moment system delivered to a mandibular central incisor during bucco-lingual tipping.
Keywords: Aligner thickness | Finite element model | Orthodontic aligner
Abstract: In the field of orthodontic planning, the creation of a complete digital dental model to simulate and predict treatments is of utmost importance. Nowadays, orthodontists use panoramic radiographs (PAN) and dental crown representations obtained by optical scanning. However, these data do not contain any 3D information regarding tooth root geometries. A reliable orthodontic treatment should instead take into account entire geometrical models of dental shapes in order to better predict tooth movements.This paper presents a methodology to create complete 3D patient dental anatomies by combining digital mouth models and panoramic radiographs. The modeling process is based on using crown surfaces, reconstructed by optical scanning, and root geometries, obtained by adapting anatomical CAD templates over patient specific information extracted from radiographic data. The radiographic process is virtually replicated on crown digital geometries through the Discrete Radon Transform (DRT). The resulting virtual PAN image is used to integrate the actual radiographic data and the digital mouth model. This procedure provides the root references on the 3D digital crown models, which guide a shape adjustment of the dental CAD templates. The entire geometrical models are finally created by merging dental crowns, captured by optical scanning, and root geometries, obtained from the CAD templates.
Abstract: The use of numerical and experimental methods to determine the stress field of mechanical components is well known. In particular, 3D photoelasticity can be considered the only experimental technique for the complete stress state evaluation of 3D components. The advent of rapid prototyping techniques has allowed the manufacturing of complex models in a matter of hours by using birifrangent materials. The present paper is focused on the description of a Computer Aided Engineering (CAE) approach which combines Finite Element (FE) simulations and automatic photoelastic investigations for the stress analysis of face gear drives, made by stereolithography. Computer Aided Design (CAD) geometries, used to manufacture the stereolithographic models, are directly used to perform FE analyses, thus allowing the stress analysis process to become simpler and easier. The substantial agreement observed between experimental and numerical results proved the potentialities of the adopted approach and the usefulness of FE simulations to optimize photoelastic analyses through cost- and time-effective experiments even for complex 3D shapes.
Keywords: Face gear models | 3D photoelasticity | FEA | Stereolithography
Abstract: The reconstruction of tooth anatomies is of utmost importance when dental implant surgeries and/or orthodontic corrections must be planned. In the last few years, cone beam CT (CBCT) has gained popularity in dentistry for 3D imaging of jawbones and teeth. However, within CBCT data sets, each tooth is defined by a region, which cannot be easily separated from surrounding tissues (i.e., bone tissue) by only considering pixel's grey-intensity values. For this reason, some enhancement is usually necessary in order to properly segment tooth geometries. In this paper, a semi-automatic approach to reconstruct individual 3D tooth anatomies by processing CBCT-scan data is presented. The methodology is based on the creation of a minimal number of 2D "local ray-sum" images by adding the absorption values of adjacent voxels along the most significant views for each tooth. The knowledge of the specific anatomical patient morphology drives the selection of these significant projection directions. The reconstructed "ray-sum" images greatly enhance the clearness of the root contours, which can then be interactively traced by dentists. A set of meaningful 2D tooth contours is consequently obtained and used to automatically extract a cubic spline curve for each transverse slice, thus approximating the overall 3D tooth profile. The effectiveness of the methodology has been evaluated by comparing the results obtained for the reconstruction of anterior teeth with those obtained by using classical segmentation tools provided within commercial software.
Abstract: The geometrical reconstruction of centrifugal pump impellers is a strategic activity for many manufacturing industries. In particular, the digitalization of internal hydraulic shapes represents the most critical task due to the difficulties in accessing the internal parts of impeller disks. In this paper, an automatic approach to digitize the internal shape of impellers is presented. The methodology is based on the integration of optical and probing methods in order to combine the advantages of both technologies. The developed approach uses an optically tracked hand-held probe designed to digitize, point-by-point, the whole surface of blades. The tracking system is based on a passive device, composed of two stereo cameras, which is used to accurately locate a specific plate, rigidly connected to a probe. The proposed methodology has been validated by experimental tests on primitive surfaces as plane, cylinders and spheres. Nonetheless, the robustness and flexibility of the developed technique has allowed the whole reconstruction of industrial impellers through the acquisition of hundreds of points in few minutes.
Abstract: Within the orthodontic field, malocclusion problems are usually treated by using different types of appliances. In particular, Eruption Guidance Appliances (EGAs) are recommended for early orthodontic treatment or prevention of malocclusion problems. The traditional approach with EGAs is based on the use of standard prefabricated appliances. Experts in the orthodontic field believe that the customization of the EGAs would strongly enhance the results of malocclusion treatments. This paper presents an innovative methodology for the design and manufacturing of fully customized EGAs. The methodology is based on an extensive integration between traditional orthodontic procedures with advanced computer aided design processes. The methodology moves from the digitalization of the plaster models obtained by optical scanning techniques. The patient morphology is then exploited, under dental practitioner supervision, for the design of the appliance geometry through CAD modeling tools. Medical guided assessment is required throughout the most of the data elaboration processes, in order to design the EGAs accordingly to the patient's clinical conditions. Low-pressure injection molds for the physical manufacturing of the appliances are then 3D printed by using rapid prototyping techniques. The proposed methodology allows the production of patient customized appliances guaranteeing low cost manufacturing and high quality standards, similar to those typically obtained by in series productions. Moreover, the presented approach offers a high integration level with numerical and finite element methods, which can be used for evaluating the stress applied on the EGA, thus allowing the reinforcement of the appliance prior its manufacturing.
Abstract: In dentistry, standard radiographic imaging is a minimally invasive approach for anatomic tissue visualization and diagnostic assessment. However, this method does not provide 3D geometries of complete dental shapes, including crowns and roots, which are usually obtained by Computerized Tomography (CT) techniques. This paper describes a shape modelling process based on multi-modal imaging methodologies. In particular, 2D panoramic radiographs and 3D digital plaster casts, obtained by an optical scanner, are used to guide the creation of both shapes and orientations of complete teeth through the geometrical manipulation of general dental templates. The proposed methodology is independent on the tomographic device used to collect the panoramic radiograph.
Keywords: Dental shape modelling | Discrete radon transform | Multi-modal imaging | PAN radiograph
Abstract: Rapid Prototyping methods are often based on additive manufacturing strategies. Depending on the application, it can also be considered the use of a removal manufacturing rapid prototyping methodology. In this paper the authors investigate the possibility of using the ultrasound technology for the shaping of materials that can be considered as a final object, or as a rapid manufactured mold for the creation of prototypes. In this case, free-form objects can be manufactured starting from foam like materials, and model the foam through the use of a ultrasonic horn thus shaping the desired features. The authors tested the possibility of implementing the technology onto automated systems, allowing considering the use of this system on automated manufacturing lines. Geometrical deviations from the 3D model are measured and material morphology before and after machining is analyzed.
Abstract: The accurate reconstruction of a human digital dental model represents a wide research area within the orthodontic field due to its importance for the customization of patient treatments. Usually, 3-D dental root geometries are obtained by segmenting tomographic data. However, concerns about radiation doses may be raised since tomographic scans produce a greater X-ray dose than conventional 2-D panoramic radiographs (PAN). The present work is aimed at investigating the possibility to retrieve 3-D shape of individual teeth by exposing the patient to the minimum radiation dose. The proposed methodology is based on adapting general CAD templates over patient-specific dental anatomy, which is reconstructed by integrating the optical digitization of dental plaster models with a PAN image. The radiographic capturing process is simulated through the Discrete Radon Transform (DRT) and performed onto the patient crowns geometry obtained by segmenting the digital plaster model. A synthetic PAN image is then reconstructed and used to integrate the radiographic data within the digitized plaster model, thus allowing to retrieve roots information which guide the CAD templates adapting over the patient anatomy.
Abstract: In the last decades, research in the orthodontic field has focused on the development of more comfortable and aesthetic appliances such as thermoformed aligners. Aligners have been used in orthodontics since the mid 20-century. Nonetheless, there is still not enough knowledge about how they interact with teeth. This paper is focused on the development of a Finite Element Method (FEM) model to be used in the optimization process of geometrical attributes of removable aligners. The presented method integrates Cone Beam Computed Tomography (CBCT) data and optical data in order to obtain a customized model of the dental structures, which include both crown and root shapes. The digital simulation has been focused on analyzing the behavior of three upper frontal teeth. Moreover, the analyses have been carried out by using different aligners' thicknesses with the support of composite structures polymerized on teeth surfaces while simulating a 2 degrees rotation of an upper central incisor.
Abstract: Dental panoramic tomography represents a standard imaging modality in dentistry since it provides a convenient and inexpensive method to visualize anatomic structures and pathologic conditions with low radiation doses. However, this technique does not provide comprehensive 3D geometries of dental shapes which are conventionally demanded to computerised tomography (CT) techniques. In this paper, a tooth reconstruction process is presented by integrating patient-specific information with general dental templates. A 2D panoramic radiograph and the digitised patient plaster cast are used to customise both shape and orientation of teeth templates thus allowing a consistent 3D tooth reconstruction with minimally invasive imaging modalities. The proposed methodology does not make any assumption about the tomographic device used to collect the panoramic radiograph. Copyright © 2014 SCITEPRESS - Science and Technology Publications. All rights reserved.
Keywords: Customised Tooth Reconstruction | Digital Cast | Discrete Radon Transform | Panoramic Radiograph
Abstract: The FBS model describes theoretically the design process of a product. Only few papers present real industrial case studies, which are generally finalized to illustrate theoretical concepts. The aim of this paper is to show a methodology and its testing on the design of new tasting glasses, based both on the FBS model and on experimental analysis. This is an interesting theme in the food design area. Indeed a tasting glass is the interface used to convey wine characteristics to human senses (sight, taste and smell). The glass influence on the evolution of sensory perception of wine is not fully understood and rarely evaluated. The analysis is composed of: (i) an experimental activity to understand the evolution of sensory profiles of a well-structured red wine maintained in different types of glasses through expert testers, (ii) the selection of one of the most important function carried on by the product, and therefore the study of the related behaviours, (iii) the identification of the correlation between the behaviours and the design parameters of the glass. Finally a method and tools to extract and measure the geometrical feature of the glass are presented. © 2013 The Design Society.
Keywords: Design methodology | Design practice | Functional analysis | Functional modelling | New product development
Abstract: Coded Structured Light techniques represent one of the most attractive research areas within the field of optical metrology. The coding procedures are typically based on projecting either a single pattern or a temporal sequence of patterns to provide 3D surface data. In this context, multi-slit or stripe colored patterns may be used with the aim of reducing the number of projected images. However, color imaging sensors require the use of calibration procedures to address crosstalk effects between different channels and to reduce the chromatic aberrations. In this paper, a Coded Structured Light system has been developed by integrating a color stripe projector and a monochrome camera. A discrete coding method, which combines spatial and temporal information, is generated by sequentially projecting and acquiring a small set of fringe patterns. The method allows the concurrent measurement of geometrical and chromatic data by exploiting the benefits of using a monochrome camera. The proposed methodology has been validated by measuring nominal primitive geometries and free-form shapes. The experimental results have been compared with those obtained by using a time-multiplexing gray code strategy. © 2013 by the authors; licensee MDPI, Basel, Switzerland.
Keywords: 3D shape acquisition | Coded Structured Light | De Bruijn pattern | Texture reconstruction
Abstract: Objectives. To build a 3D parametric model to detect shape and volume of dental roots, from a panoramic radiograph (PAN) of the patient. Materials and Methods. A PAN and a cone beam computed tomography (CBCT) of a patient were acquired. For each tooth, various parameters were considered (coronal and root lengths and widths): these were measured from the CBCT and from the PAN. Measures were compared to evaluate the accuracy level of PAN measurements. By using a CAD software, parametric models of an incisor and of a molar were constructed employing B-spline curves and free-form surfaces. PAN measures of teeth 2.1 and 3.6 were assigned to the parametric models; the same two teeth were segmented from CBCT. The two models were superimposed to assess the accuracy of the parametric model. Results. PAN measures resulted to be accurate and comparable with all other measurements. From model superimposition the maximum error resulted was 1.1 mm on the incisor crown and 2 mm on the molar furcation. Conclusion. This study shows that it is possible to build a 3D parametric model starting from 2D information with a clinically valid accuracy level. This can ultimately lead to a crown-root movement simulation. © 2013 Laura Mazzotta et al.
Abstract: In the field of dental health care, plaster models combined with 2D radiographs are widely used in clinical practice for orthodontic diagnoses. However, complex malocclusions can be better analyzed by exploiting 3D digital dental models, which allow virtual simulations and treatment planning processes. In this paper, dental data captured by independent imaging sensors are fused to create multi-body orthodontic models composed of teeth, oral soft tissues and alveolar bone structures. The methodology is based on integrating Cone-Beam Computed Tomography (CBCT) and surface structured light scanning. The optical scanner is used to reconstruct tooth crowns and soft tissues (visible surfaces) through the digitalization of both patients' mouth impressions and plaster casts. These data are also used to guide the segmentation of internal dental tissues by processing CBCT data sets. The 3D individual dental tissues obtained by the optical scanner and the CBCT sensor are fused within multi-body orthodontic models without human supervisions to identify target anatomical structures. The final multi-body models represent valuable virtual platforms to clinical diagnostic and treatment planning. © 2013 by the authors; licensee MDPI, Basel, Switzerland.
Keywords: Dental CBCT images | Optical scanning | Orthodontic model | Sensor fusion | Tooth segmentation
Abstract: Recent developments in digital imaging techniques have allowed a wide spread of three-dimensional methodologies based on capturing anatomical tissues by different approaches, such as cone-beam computed tomography, three-dimensional photography and surface scanning. In oral rehabilitation, an objective method to predict surgical and orthodontic outcomes should be based on anatomical data belonging to soft facial tissue, facial skeleton and dentition (maxillofacial triad). However, none of the available imaging techniques can accurately capture the complete triad. This article presents a multi-modal framework, which allows image fusion of different digital techniques to create a three-dimensional virtual maxillofacial model, which integrates photorealistic face, facial skeleton and dentition. The methodology is based on combining structured light surface scanning and cone-beam computed tomography data processing. The fusion procedure provides multi-modal representations by aligning different tissues on the basis of common anatomical constraints. © IMechE 2012.
Keywords: Computer assisted | Cone-beam computed tomography scanning | Maxillofacial modelling | Multi-modal image fusion | Optical scanning | Three-dimensional medical imaging
Abstract: Three-dimensional shapes can be digitised by using active imaging techniques, which reconstruct entire objects by capturing multiple range maps from different viewpoints. Multiple-view reconstructions require the computation of translation and rotation parameters to transform each range map with reference to a global coordinate frame. In this paper, an automatic method has been developed to efficiently align 3D range maps acquired by an active stereo vision system. The methodology is based on referring range maps to a global frame of fiducial markers captured by the stereo system. The procedure includes a refinement of the marker frame in order to globally minimise the misalignment errors. The methodology optimises the overall accuracy of 3D reconstructions regardless of the scanning strategies, even processing large data sets. The proposed approach has been experienced and validated by measuring both nominal shapes and industrial models. © 2012 Elsevier Ltd. All rights reserved.
Keywords: 3D optical scanning | Global refinement | Marker detection | Multi-view measurements | Stereo-vision
Abstract: In the field of oral rehabilitation, innovative methodologies based on the combined use of 3D imaging technologies and computer-guided approaches, have been developed with the aim at defining reliable tools for the virtual preoperative assessment of implant placement. The accurate and reliable transfer of the virtual planning into the surgical field represents the main challenge for modern implantology. This paper aims at defining and verifying the clinical applicability of an innovative CAD/CAM framework for the accurate planning of dental implant surgeries based on the integration of Computed Tomography (CT) and surface optical scanning. The higher accuracy and resolution of optical scanning allows a more accurate reconstruction of dentition structures and mouth soft tissues, thus guaranteeing a better fitting of the designed prosthetic structures with respect to the patient oral cavity. © 2012 IEEE.
Keywords: 3D virtual model reconstruction | computer-assisted dental implantology | oral rehabilitation
Abstract: The creation of three-dimensional virtual models by optical technologies typically involve uncontrolled metric errors, in particular, when small high-resolution 3-D imaging systems are used to reconstruct a large object. Within Cultural Heritage, the problem of metric accuracy is a major issue and no methods are currently available for controlling and enhancing it. This paper presents a methodology based on the integration of a 3D range camera system with an optical tracking technique. The basic idea is the generation of a global coordinate system determined by the optical tracker, which controls the rigid motions of the 3D range camera system during multi-scan processes. The tracking process is based on measuring the spatial coordinates of reference markers located onto the range camera. The metric reliability of the 3D model reconstruction is guaranteed to a known acceptable level. Experimental results on a Statue of Hope located at the English Cemetery in Florence, are also reported. © 2012 IEEE.
Keywords: 3D reconstruction | Cultural Heritage | optical tecquiques
Abstract: Recent advances in 3D imaging techniques have provided flexible tools for clinical assessments within many medical fields. In the field of orthodontic and orthognathic surgery, the reliable creation of 3D anatomical models can assist clinicians for both diagnosis and treatment planning. In particular, the accurate integration between facial soft tissue, facial skeleton and dentition (maxillofacial triad) provides clinicians with a complete model for virtual 3D treatment planning. However, none of the existing imaging technologies is able to simultaneously capture the complete triad with the optimal resolution and accuracy. For this reason, a "model fusion" process must be carried out in order to integrate 3D models obtained using different imaging techniques. This paper aims at introducing a procedure to create accurate maxillofacial triad models by guiding the fusion of multi-modal 3D imaging techniques. The methodology is based on integrating a structured light optical scanner with Cone-Beam Computed Tomography (CBCT) data processing in order to capture the different tissue groups composing the maxillofacial triad. The generated models represent an all-embracing virtual workbench for orthodontists in the treatment planning of malocclusion problems and for surgeons in the preoperative prediction of surgical outcomes. © 2012 IEEE.
Keywords: 3D image fusion processes | 3D reconstruction | maxillofacial model
Abstract: Nowadays, optical sensors are used to digitize sculptural artworks by exploiting various contactless technologies. Cultural Heritage applications may concern 3D reconstructions of sculptural shapes distinguished by small details distributed over large surfaces. These applications require robust multi-view procedures based on aligning several high resolution 3D measurements. In this paper, the integration of a 3D structured light scanner and a stereo photogrammetric sensor is proposed with the aim of reliably reconstructing large free form artworks. The structured light scanner provides high resolution range maps captured from different views. The stereo photogrammetric sensor measures the spatial location of each view by tracking a marker frame integral to the optical scanner. This procedure allows the computation of the rotation-translation matrix to transpose the range maps from local view coordinate systems to a unique global reference system defined by the stereo photogrammetric sensor. The artwork reconstructions can be further augmented by referring metadata related to restoration processes. In this paper, a methodology has been developed to map metadata to 3D models by capturing spatial references using a passive stereo-photogrammetric sensor. The multi-sensor framework has been experienced through the 3D reconstruction of a Statue of Hope located at the English Cemetery in Florence. This sculptural artwork has been a severe test due to the non-cooperative environment and the complex shape features distributed over a large surface. © 2012 by the authors; licensee MDPI, Basel, Switzerland.
Keywords: 3D imaging sensors | 3D reference information system | Cultural heritage | Stereo-photogrammetry | Structured light scanning
Abstract: In the shipbuilding industry, the manufacturing of large yacht hulls is a complex process. Metal hulls are traditionally manufactured by welding pre fabricated large steel panels to form the external superstructure. A surface finishing process is then carried out in order to obtain a final target surface having a smooth curvature. The methodologies manly rely on manual processes based on the measurement of the as built hull shape through simple testing instrumentation. Well-experienced workers are required, and a great amount of time is usually wasted, thus affecting the overall shipyard competitiveness. This paper introduces a methodology for automating the measurement process of as built hull yacht shapes. The methodology, which is based on the integration of a robotic system with an optical scanner, provides accurate non contact 3D full field measurements of the hull surface. The placement of the robotic system around the hull shape is determined by a laser total station thus allowing the automatic multi view data registration into a common reference frame. The proposed approach represents the basis for the automation of the whole surface finishing process of large yacht hulls. In this paper, the methodology has been tested by measuring a large broadside area of a 59 m hull assembled within a shipyard. © 2012 Elsevier Ltd. All rights reserved.
Keywords: Laser tracking | Mechanical tracking | Optical 3D measurement | Shipbuilding
Abstract: Background: A fundamental pre-requisite for the clinical success in dental implant surgery is the fast and stable implant osseointegration. The press-fit phenomenon occurring at implant insertion induces biomechanical effects in the bone tissues, which ensure implant primary stability. In the field of dental surgery, the understanding of the key factors governing the osseointegration process still remains of utmost importance. A thorough analysis of the biomechanics of dental implantology requires a detailed knowledge of bone mechanical properties as well as an accurate definition of the jaw bone geometry.Methods: In this work, a CT image-based approach, combined with the Finite Element Method (FEM), has been used to investigate the effect of the drill size on the biomechanics of the dental implant technique. A very accurate model of the human mandible bone segment has been created by processing high resolution micro-CT image data. The press-fit phenomenon has been simulated by FE analyses for different common drill diameters (D A = 2.8 mm, D B = 3.3 mm, and D C = 3.8 mm) with depth L = 12 mm. A virtual implant model has been assumed with a cylindrical geometry having height L = 11 mm and diameter D = 4 mm.Results: The maximum stresses calculated for drill diameters D A, D B and D C have been 12.31 GPa, 7.74 GPa and 4.52 GPa, respectively. High strain values have been measured in the cortical area for the models of diameters D A and D B, while a uniform distribution has been observed for the model of diameter D C . The maximum logarithmic strains, calculated in nonlinear analyses, have been ε{lunate} = 2.46, 0.51 and 0.49 for the three models, respectively.Conclusions: This study introduces a very powerful, accurate and non-destructive methodology for investigating the effect of the drill size on the biomechanics of the dental implant technique.Further studies could aim at understanding how different drill shapes can determine the optimal press-fit condition with an equally distributed preload on both the cortical and trabecular structure around the implant. © 2012 Frisardi et al.; licensee BioMed Central Ltd.
Abstract: In recent years, various methodologies of shape reconstruction have been proposed with the aim at creating Computer-Aided Design models by digitising physical objects using optical sensors. Generally, the acquisition of 3D geometrical data includes crucial tasks, such as planning scanning strategies and aligning different point clouds by multiple view approaches, which differ for user's interaction and hardware cost. This paper describes a methodology to automatically measure three-dimensional coordinates of fiducial markers to be used as references to align point clouds obtained by an active stereo vision system based on structured light projection. Intensity-based algorithms and stereo vision principles are combined to detect passive fiducial markers localised in a scene. 3D markers are uniquely recognised on the basis of geometrical similarities. The correlation between fiducial markers and point clouds allows the digital creation of complete object surfaces. The technology has been validated by experimental tests based on nominal benchmarks and reconstructions of target objects with complex shapes. © Springer-Verlag 2011.
Keywords: Digital image processing | Marker detection | Multiple view scanning | Reverse engineering | Stereo vision
Abstract: Full field optical techniques can be reliably used for 3D measurements of complex shapes by multi-view processes, which require the computation of transformation parameters relating different views into a common reference system. Although, several multi-view approaches have been proposed, the alignment process is still the crucial step of a shape reconstruction. In this paper, a methodology to automatically align 3D views has been developed by integrating a stereo vision system and a full field optical scanner. In particular, the stereo vision system is used to remotely track the optical scanner within a working volume. The tracking system uses stereo images to detect the 3D coordinates of retro-reflective infrared markers rigidly connected to the scanner. Stereo correspondences are established by a robust methodology based on combining the epipolar geometry with an image spatial transformation constraint. The proposed methodology has been validated by experimental tests regarding both the evaluation of the measurement accuracy and the 3D reconstruction of an industrial shape. © 2011 Elsevier Ltd. All rights reserved.
Keywords: Multi-view measurements | Optical tracking | Stereo vision | Structured light
Abstract: Current research on underwater 3D imaging methods is mainly addressing long range applications like seafloor mapping or surveys of archeological sites and shipwrecks. Recently, there is an increasing need for more accessible and precise close-range 3D acquisition technologies in some application fields like, for example, monitoring the growth of coral reefs or reconstructing underwater archaeological pieces that in most cases cannot be recovered from the seabed. This paper presents the first results of a research project that aims to investigate the possibility of using active optical techniques for the whole-field 3D reconstructions in an underwater environment. In this work we have tested an optical technique, frequently used for in air acquisition, based on the projection of structured lighting patterns acquired by a stereo vision system. We describe the experimental setup used for the underwater tests, which were conducted in a water tank with different turbidity conditions. The tests have evidenced that the quality of 3D reconstruction is acceptable even with high turbidity values, despite the heavy presence of scattering and absorption effects. © 2011 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).
Keywords: 3D reconstruction | Imaging in turbid medium | Photogrammetry | Structured light | Underwater imaging
Abstract: Background: A precise placement of dental implants is a crucial step to optimize both prosthetic aspects and functional constraints. In this context, the use of virtual guiding systems has been recognized as a fundamental tool to control the ideal implant position. In particular, complex periodontal surgeries can be performed using preoperative planning based on CT data. The critical point of the procedure relies on the lack of accuracy in transferring CT planning information to surgical field through custom-made stereo-lithographic surgical guides.Methods: In this work, a novel methodology is proposed for monitoring loss of accuracy in transferring CT dental information into periodontal surgical field. The methodology is based on integrating 3D data of anatomical (impression and cast) and preoperative (radiographic template) models, obtained by both CT and optical scanning processes.Results: A clinical case, relative to a fully edentulous jaw patient, has been used as test case to assess the accuracy of the various steps concurring in manufacturing surgical guides. In particular, a surgical guide has been designed to place implants in the bone structure of the patient. The analysis of the results has allowed the clinician to monitor all the errors, which have been occurring step by step manufacturing the physical templates.Conclusions: The use of an optical scanner, which has a higher resolution and accuracy than CT scanning, has demonstrated to be a valid support to control the precision of the various physical models adopted and to point out possible error sources. A case study regarding a fully edentulous patient has confirmed the feasibility of the proposed methodology. © 2011 Frisardi et al; licensee BioMed Central Ltd.
Abstract: Chronic wounds represent a particular debilitating health care problem, mainly affecting elderly people. A full and correct diagnosis of tissue damage should be carried out considering both dimensional, chromatic, and thermal parameters. A great variety of methods have been proposed with the aim of producing objective assessment of skin lesions, but none of the existing technologies seem to be robust enough to work for all ulcer typologies. This paper describes an innovative and non-invasive system that allows the automatic measurement of non-healing chronic wounds. The methodology involves the integration of a three-dimensional (3D) optical scanner, based on a structured light approach, with a thermal imager. The system enables the acquisition of geometrical data, which are directly related to chromatic and temperature patterns through a mapping procedure. Damaged skin areas are detected by combining visible and thermal imaging. This approach allows for the automatic measurement of extension and depth of ulcers, even in the absence of significant and well-defined chromatic patterns. The proposed technology has been tested in the measurement of ulcers on human legs. Clinical tests have demonstrated the effectiveness of this methodology in supporting medical experts for the assessment of chronic wounds. © 2011 Authors.
Keywords: 3D model reconstruction | 3D thermography | image processing | wound assessment
Abstract: In the last few years, many methodologies of reverse engineering have been proposed for 3D shape measurement using optical systems. All the proposed 3D scanning solutions require user interactions concerning the alignment process of partial measures to reconstruct the complete shape of a target object. This paper presents an innovative solution based on the integration of a robotic arm and an optical stereo system, which minimizes user intervention both in the acquisition and in the reconstruction phases. The procedure is divided into two steps: 1) complete and accurate identification of the integrated system, using optical measurements of a reference surface (calibration process); 2) planning of scanning strategies in order to automatically obtain a complete 3D CAD representation. Results of experimental tests conducted on nominal samples and on industrial contexts are presented and discussed. © 2010 Taylor & Francis Group.
Abstract: Complex periodontal surgeries can be performed using preoperative planning based on CT or MRI data that permit a 3D reconstruction of the patient bone anatomy. This allows a more accurate assessment of the surgical difficulties by the surgeon. The precise placement of dental implants is a crucial step to optimize both prosthetic considerations and functional aspects and the use of physical guiding systems has been recognized as a fundamental tool to control their positions and angulations. The weak point of the procedure relies on the accuracy of transferring CT planning information to the surgical field by means of custom-made stereolithographic guides. This paper concerns the study of an innovative methodology for the monitoring of the loss in the clinical accuracy through the various steps concurring in this transfer. The procedure is based on the integration of an optical scanner, with a structured coded light approach, within the CT scan based preoperative planning process. The higher resolution and accuracy, compared to CT scanning systems, has allowed for the use of the optical scanner as a standard to evaluate the precision of CT data and fabrication processes of the guiding templates. A clinical case if finally presented and discussed. © 2010 Taylor & Francis Group.
Abstract: Chronic wounds represent one of the most frequent pathologies affecting elderly people. In the last few years, several methods have been proposed with the aim at developing systems able to produce automatic and objective assessment of skin ulcers. Despite that, none of the existing technologies seems to be robust enough to work for all the ulcer typologies. In the majority of the clinical contexts, the evaluation of chronic wounds still depends on the experience of physicians rather than on the use of numerically objective attributes. This paper presents a non-invasive methodology to allow automatic measurements of chronic wounds. The proposed system involves the development of a 3D optical scanner, based on a structured light approach, combined with an infrared detector. This arrangement permits the acquisition of geometrical data including both chromatic texture and temperature information. A tool for the automatic detection of damaged skin areas has been developed by segmenting both color and thermal images, making possible to reliably quantify parameters characterizing wounds, such as area, depth and volume, even in absence of a perceptible color characterization. The described technology has been finally experienced in medical environment, proving its effectiveness for an objective assessment of wound healing.
Keywords: 3D segmentation | 3D thermography | Imaging | Wound modelling
Abstract: Range maps registration still represents one of the most time consuming phases in the digitization of 3D shapes due to the high user intervention required. The traditional approaches are, in fact, based on manual rough alignments, followed by ICP refining techniques. On the other hand, existing unattended methodologies, based on the automatic searching for correspondent morphological singularities on adjacent point clouds, do not seem to guarantee sufficient robustness and flexibility in the fast reconstruction of target objects. This paper presents a methodology to acquire free-form shapes by combining a 3D stereo vision system and a fully automatic range maps registration process. The automatic alignment is carried out without any assumptions about the initial positions of the point clouds and is based on the automatic detection of fiducial markers, located on the surface object, by processing grey intensity images. © 2008 Taylor & Francis Group.
Abstract: In this contribution we describe the modern 2D and 3D technologies for the documentation, analysis and restoration of paintings. RGB color imaging, IR and UV fluorescence sensors, together with highly precise active sensors are among the most widely technologies in this field. The devices provide information on the painting's materials, on the employed technique and on the conservation's state of the art work. However, all information must be correctly registered to be able to draw safe conclusions and perform the most adequate conservation interventions. We also present a complete example where multispectral visible images, IR refiectography, UV fluorescence and 3D data are acquired and then combined, showing how the integration gives a new and significant improvement in the analysis of painting. © 2007 SPIE-IS&T.
Keywords: 3D sensing | Cultural heritage | Image registration | Multispectral imaging | Reflectography
Abstract: This paper presents a 3D optical digitiser based on an active stereo vision aproach. The system is composed of a digital camera, a multimedia projector and software to control the hardware and process the images. The proposed solution integrates an active coded light method with a photogrammetric procedure in order to allow the acquisition of complex surfaces. In the work, experimental tests have been conducted with a nominal model and styling components of two-wheeler vehicles. The measurement process and the experimental results have been analysed to verify usability and accuracy of the methodology.
Keywords: Coded light | Photogrammetry | Reverse Engineering | Stereovision