L. Barrenetxea

Direct transfer of the position of digitized casts to a virtual articulator

This article describes a digital technique to transfer the location of digitized casts obtained directly from the patient to a virtual articulator (digital/virtual facebow transfer). The primary advantage of this technique is that it allows the dentist and the dental laboratory technician to work in a fully digital environment without having to mount stone casts on a physical articulator. This results in a significant time reduction and a higher degree of accuracy in the cast location.

Comparison of the accuracy of a 3-dimensional virtual method and the conventional method for transferring the maxillary cast to a virtual articulator

STATEMENT OF PROBLEM The currently available virtual articulators fail to locate the digitized maxillary cast at the exact position in the virtual environment. Some locate the casts on a mechanical articulator with a facebow, and this position is then digitized for the virtual environment. PURPOSE The purpose of this study was to compare the location of the maxillary cast on an articulator by using 2 different procedures: the conventional method and a virtual method. MATERIAL AND METHODS With the conventional procedure, the kinematic axis of the participant was determined with an axiograph. The location of the maxillary cast in reference to this axis was then physically transferred to a Panadent mechanical articulator. By a virtual procedure, the same kinematic axis and the maxillary cast were transferred directly from the participant to the Panadent virtual articulator by means of reverse engineering devices. The locations obtained with both procedures were compared in a virtual environment with an optical scanner. By calculating the deviation at every point of the occlusal surface, the results obtained with this procedure were then compared with those of the conventional method. RESULTS The mean deviation on the occlusal surface was 0.752 mm, and the standard deviation was 0.456 mm. CONCLUSIONS The deviation between the procedures was sufficiently small to allow the methodology for orthodontic purposes. However, the accuracy of the virtual procedure should be improved so as to extend its use to other fields, such as orthognathic surgery or dental restorations, in which the clinical technique requires an articulator.

Computer-aided dental prostheses construction using reverse engineering.

The implementation of computer-aided design/computer-aided manufacturing (CAD/CAM) systems with virtual articulators, which take into account the kinematics, constitutes a breakthrough in the construction of customised dental prostheses. This paper presents a multidisciplinary protocol involving CAM techniques to produce dental prostheses. This protocol includes a step-by-step procedure using innovative reverse engineering technologies to transform completely virtual design processes into customised prostheses. A special emphasis is placed on a novel method that permits a virtual location of the models. The complete workflow includes the optical scanning of the patient, the use of reverse engineering software and, if necessary, the use of rapid prototyping to produce CAD temporary prostheses.

Retrieval of unfiltered digitized cylindrical surfaces based on spin-images

In current design and manufacturing processes, the verification of tolerances is mainly focused on dimensional tolerances. As a general rule, manufacturing instructions specify dimensional tolerances and surface qualities. However, geometric tolerances are hardly ever specified, and this often leads to a lack of adequacy of the design. A better adequacy of this design would certainly produce a significant reduction in manufacturing costs. The lack of trained engineers, as well as the non-availability of the appropriate software, has relegated geometric tolerances, at the very best, to a second place. One of the greatest difficulties when using the current software solutions is the partition and identification of the meshes obtained from a scanning process on specific features. These processes can hardly be carried out via automation because they are subject to the accuracy of the tool and the skill of the technician in charge of processing the meshes. This paper presents a semi-automatic process to detect non-ideal, cylindrical features in point clouds. Its aim is to identify and extract the points from these features in order to implement them into the verification algorithms of possible associated geometric tolerances. In this process, spin-images, usually developed in the detection of shapes, are used as a graphic tool.

A new method to capture the jaw movement

In traditional dentistry, orthodontics and maxillo-facial surgery, articulators are mainly used to simulate the dental occlusion. Dental implants and syndromes such as functional occlusion require instrumentation for the planning previous to the surgery. There are various mechanical articulators on the market. However, most of them only simulate the rotation of the jaw about an axis running through the virtual condyles. However, the real movement includes translation and rotation and differs from one patient to another. Surgeons and dentists require a comprehensive simulation system as a support for their work. This article describes the work carried out to develop a method to capture mandibular movement. Taking into consideration the market proposals and in comparison with them, this system is intended to be as cheap and simple as possible.

Collision Free Design of Dental Prosthesis

This research project presents the construction of a Dental Virtual Articulator that permits the design of collision-free geometry on dental prostheses. Thanks to this articulator kinematic analysis can be taken into account in the design of dental prostheses. This is an improvement of the utmost importance in this field. Several steps have been followed in the development of this virtual articulator. First, in order to obtain a digitalized data of each individual patient, plaster models of his/her upper and lower parts of the jaw were scanned. Afterwards, depending on the required accuracy or on the patient’s setting data available in each case, the type of articulator was selected. Then, using a CAD system, the missing teeth were statically modelled. Also, the opening/closing movements and the lateral occlusion were simulated with the CAD system in order to analyze possible occlusal collisions and modify the design accordingly. Finally, this paper discusses the still existing shortcomings of virtual articulator simulation and provides a detailed research prospect as well. The main practical implications of this paper are, on the one hand, the improvement in dental CAD/CAM systems by adding the kinematic analysis, and on the other, since each of them has an individual pattern of movement, the analysis of the simulations of different articulators.