Objectives: Rapid development of digital technologies and 3D printing provide new tools for orthodontic indirect bonding. The purpose of this in-vitro study is to evaluate the clinical acceptability of hard CAD/CAM indirect bonding tray. Material & Methods: Ten soft silicone transfer trays and ten hard CAD/CAM trays were produced and 200 brackets were placed on them. The brackets were then transferred to twenty SLA-printed models by indirect bonding. These models were scanned and digitally compared to the reference model by three-dimensional superimpositions (GOM software). The linear and angular measurements were collected and analysed. Results: For the CAD/CAM trays, 100% of the mesiodistal, vertical and transverse measurements of incisors were within the clinical acceptable range of the American Board of Orthodontists (ABO) standards. More specifically, the clinically acceptable linear measurements were between 97 to 100% for silicone trays while they were between 89 to 100% for CAD/CAM trays. The clinically acceptable angular measurements varied between 87% and 100% for the silicone trays and between 79% and 100% for the CAD/CAM trays. Silicone trays were more precise than CAD/CAM trays. The difference was significant for all linear and angular measurements. Conclusions: While the CAD/CAM group shows clinically acceptable results according to the ABO, silicone remains to be more precise than CAD/CAM for transfer trays and is therefore still the reference. Clinical relevance: We demonstrate here that the orthodontic indirect bondings, whether they are realized using silicone transfer trays or CAD/CAM trays, are clinically acceptable in terms of the repositioning accuracy of brackets.

A mathematical model of dual-component paramagnetic and diamagnetic material to cancel metal-induced MRI artifacts was developed and verified experimentally. The magnetization produced by metallic material and then the gradient linearity distortion can be cancelled by using such materials with opposing paramagnetic and diamagnetic properties. This concept of dual-component materials provides a novel solution to the problem of MRI artifacts.

Numerical simulation is a valuable tool for the study of magnetic susceptibility artifacts from metallic implants. A major difficulty in the simulation lies in the computation of the magnetic field induced by the metallic implant. A new method has been designed and implemented to compute the magnetic field induced by metallic objects of arbitrary shape. The magnetic field is expressed pointwise in terms of a surface integral. In magnetic resonance imaging (MRI) even minor perturbations of the gradients can disturb the imaging process and may render the clinical image inaccurate or useless. Common causes of magnetic field perturbation are changes of magnetic properties in the sample due to metallic implanted objects, such as a dental prosthesis, orthopedic apparatus, etc. Metallic surgical instruments used in interventional MRI are also responsible for magnetic field perturbation. In the case of guided stereotactic surgery, image distortions are especially harmful since geometrical accuracy is required.In the past, several studies involving numerical simulation have been undertaken to help in the understanding of magnetic field perturbation and to establish experimental conditions that determine susceptibility artifacts (1-3). However, these simulation attempts have been restricted to simple test objects (cylinders, spheres, and ellipsoids) for which an analytical expression for the induced magnetic field is known. In general, a precise calculation of the magnetic field involves a boundary value problem with partial differential equations (PDE) derived from Maxwell's equations, and requires the use of PDE approximation schemes. Among the classical numerical methods are the finite element method (FEM), the finite difference method (FDM), and the boundary element method (BEM). For a comprehensive treatment of these numerical methods in electromagnetism see Ref. 4. Our approach, which is based on a surface integral representation formula for the magnetic flux density, is most similar to the BEM. In short, our method consists of expressing the problem in an integral form over the boundary of the implant, and dividing the boundary into elements in which the integral is numerically computed. It is able to deal with objects of any shape, provided that a mesh of the object boundary is available. This requirement is not at all restricting since mesh generation tools are widely used in computer assisted design (CAD). The advantages of our method compared to the FEM (5) or the FDM (6) are numerous. First, the computation depends only on the object boundary, so the discretization of space is reduced from 3D to 2D. Furthermore, in the FDM/FEM the exterior domain must be truncated and an approximation of the behavior of the field at infinity must be introduced on an artificial boundary. With the BEM, the behavior at infinity is always exactly satisfied. Finally, for 3D problems the FEM and the FDM lead to large linear systems to be solved, whereas in the proposed method the solution is obtained pointwise by evaluating a surfac...

Background Due to increasing numbers of adult patients, orthodontists are being confronted more and more with periodontal problems. Coordination amongst orthodontists, periodontists and general dentists is useful in preventing and stopping periodontal disease. The main objectives of this survey were to evaluate the technical knowledge, techniques and attitudes employed by French orthodontists, periodontists and general dentists in adult dental care. Methods A cross-sectional online survey was distributed to French dentists. The questionnaire, consisting of 30 questions, was divided into six sections covering treatment programs and the forensic environment. Results One thousand one hundred twenty-two complete answers were recorded. Adults undergoing orthodontic treatment represented 19.9% of the orthodontists' patients, but only 2.67% of the general dentists' patients. Communication between clinicians was rated as good, greater than 3 out of 5. Before treatment, orthodontists were less alarmed than generalists regarding bleeding, recessions, increased probing depths, halitosis and hyperplasia. During treatment, orthodontists never or only occasionally performed palpation or probing in 54.2% and 84.6% of cases. Gingivitis and recessions were the main reasons for consultations for 22.0% and 20.1% of general dentists and periodontists after orthodontic treatment. Of the practitioners surveyed, 43% felt that they experienced a setback in the ortho-periodontal treatment. Conclusions This study revealed discrepancies in the knowledge and attitudes of practitioners. Therapeutic management remains one of the major challenges of multidisciplinary treatments. Continuing education needs to be further developed in this field.