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

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

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 vibration measurements by a virtual-stereo-camera system based on a single low frame rate camera

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

Computational design and engineering of polymeric orthodontic aligners

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

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

Computer aided modelling to simulate the biomechanical behaviour of customised orthodontic removable appliances

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

Flexible calibration of a stereo vision system by active display

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

Interactive design of dental implant placements through CAD-CAM technologies: from 3D imaging to additive manufacturing

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

Nonlinear dependency of tooth movement on force system directions

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. Hence, limited information is available to evaluate a load system elicited by an appliance in 3D. Here, to increment 3-D tooth movement theory, we test the hypothesis that the mathematical relationships between M:F and tooth movement are distinct depending on force system directions. A finite element model of a first maxillary premolar, scaled to average tooth dimensions, was constructed based on a CBCT scan. We conducted finite element analysis (FEA) of the M:F and tooth movement relationships, represented by the projected axis of rotation (C.Rot) in each plane, for 510 different Loads. We confirmed that an hyperbolic equation relates the Distance (C.Res-C.Rot) and M:F; however, the constant of proportionality ("k") varied with non-linearly the force direction. With a force applied parallel to the tooth long axis, "k" was 12 times higher than with a force parallel to the mesio-distal direction and 7 times higher than with a force parallel to the bucco-lingual direction. The M:F has differential influence on tooth movement depending on load directions, and it is an incomplete parameter to describe the quality of an orthodontic load system if not associated with force and moment directions. Moreover, incremental differences in M:F in each plane have different incremental effects on C.Rot position