Sensor Architectures and Technologies for Upper Limb 3D Surface Reconstruction: A Review.

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.

Mechanical Properties of Thermoplastic Polymers for Aligner Manufacturing: In Vitro Study.

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.

Thickness of orthodontic clear aligners after thermoforming and after 10 days of intraoral exposure: a prospective clinical study.

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.

An Omnidirectional Vision Sensor Based on a Spherical Mirror Catadioptric System.

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.

Design and manufacturing of patient-specific orthodontic appliances by computer-aided engineering techniques.

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.

Nonlinear dependency of tooth movement on force system directions.

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.

Geometrical modeling of complete dental shapes by using panoramic X-ray, digital mouth data and anatomical templates.

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.

Kinetic responses of running shoes submitted to prolonged use: a case report / Respostas dinâmicas em calçados de corrida submetidos ao uso prolongado: um relato de caso

The purpose of this study was to analyze the kinetic responses of running shoes submitted to prolonged use. Four shoes (R1, R2, T1 and T2) were used for 500 km except for T1 which was used for 1000 km. At every 100 km, Ground Reaction Force (GRF) and plantar pressure measurements were collected. In T2, there was a slight trend of increase in Loading Rate of the first peak of GRF with increasing distance. R1, R2 and T1 showed no trend of increase in Loading Rate values. Shoe T1 showed a slight tendency of increase in Loading Rate values when the distance was considered up to 1000 km. All running shoes showed a high variability in peak pressure values, but no trend of increase was observed. On the contrary, T1, T2 and R2 showed a trend of decrease in peak pressure values with increasing use. Therefore, there is no consistent evidence or trend of increase in Loading Rate and Peak Pressure values that would suggest worsening in external load attenuation.

O objetivo foi analisar as respostas dinâmicas em calçados de corrida submetidos ao uso prolongado. Quatro calçados (R1, R2, T1 e T2) foram submetidos ao uso prolongado na corrida. R1, R2 e T2 foram usados por 500 km e T1 por 1000 km. A cada 100 km, foram coletadas a Força de Reação do Solo e a pressão plantar. Em T2, houve uma ligeira tendência de aumento na taxa de crescimento do primeiro pico de força vertical (TC1) com o aumento da quilometragem de uso. R1, R2 e T1 não mostraram tendência de aumento nos valores de TC1. O calçado T1 apresentou uma ligeira tendência de aumento nos valores de TC1 nas quilometragens de uso até 1.000 km. Todos os calçados de corrida mostraram alta variabilidade nos valores de pico de pressão, mas sem tendência clara de aumento. Pelo contrário, T1, T2 e R2 mostraram uma tendência de diminuição dos valores da pressão de pico com quilometragens crescentes de uso. Portanto, não há nenhuma evidência consistente ou tendência de aumento de nos valores de TC1 ou de pico de pressão que pudesse sugerir piora na atenuação de carga externa.

A coded structured light system based on primary color stripe projection and monochrome imaging.

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.

Computer-aided modelling of three-dimensional maxillofacial tissues through multi-modal imaging.

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.

Creation of 3D multi-body orthodontic models by using independent imaging sensors.

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.

3D reconstruction and restoration monitoring of sculptural artworks by a multi-sensor framework.

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.

Biomechanics of the press-fit phenomenon in dental implantology: an image-based finite element analysis.

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 (DA=2.8 mm, DB=3.3 mm, and DC=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 DA, DB and DC 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 DA and DB, while a uniform distribution has been observed for the model of diameter DC . The maximum logarithmic strains, calculated in nonlinear analyses, have been ϵ=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.

Integration of 3D anatomical data obtained by CT imaging and 3D optical scanning for computer aided implant surgery.

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.