Les Cahiers de prothese最新文献

After describing in Part I the preparation of diagnostic cast, the authors describe the Wax Up preparation. Most of the definition of centric relation agree that the position of the mandible is slightly behind its position in centric occlusion. The Hinge axis position is used for mounting the cast on articulator. The final restauration must reconstruct both position and the occlusion should be established in front the centric occlusion. After equilibration anterior guidance is studied and restaured if necessary. After creating the different curve of occlusion, the final Wax Up is settled. The use of the diagnostic cast so obtained will be presented in Part III.

The authors analyzed the numerous devices and prosthetic kits currently available for implant prosthodontics. Existing systems can be classified into two fundamentally different categories: the gold ring cylinder (or its equivalent in resin for casting) and the prosthetic abutment core or post concept. The former is based on connection of two nearly flat, horizontal surfaces by means of a screw, which avoids problems of parallelism; the latter can be likened to insertion of one part into another, like a crown that slides along the vertical axis of an abutment, with connection being obtained by cementation and/or screwing. Prosthetic abutment core or post: Whether monoblock or multiblock, the implant core or post is very similar to a conventional metallic abutment. Construction of the implant prosthesis is generally no problem when parallelism has been respected during surgery; if problems are encountered with parallelism, options include: 1. Adjustment of the abutment core by grinding, 2. Use of a telescope to achieve parallelism, 3. Use of a bendable prosthetic abutment core, 4. Use of a prosthetic abutment core preangulated 10 degrees-20 degrees, 5. A combination of the above solutions. The implant prostheses may be screwed, cemented or clipped in position. Gold ring cylinder concept The gold ring cylinder (or its equivalent in resin for casting) theoretically eliminates problems of parallelism, but at the same time restricts the implant prosthesis to screw techniques. A special protocol is required for the impression and construction of the prosthesis. Impression with plaster is often the best method for total edentulism whereas "open" impression trays are advisable for partial prostheses. In the laboratory, use of a machined gold ring cylinder provides optimum precision, but intra-oral verification remains necessary. Implant prosthodontics unquestionably represent a new type of "know how": both the dentist and the dental lab technician must acquire the necessary training and adapt their work routines.

The more common techniques for analysing the alveolar ridge in full dentures were examined. Both the linear analysis and the two-dimensional one, proposed by Pound, were described. The ridge-transfer method was found to be three-dimensional, thus allowing the construction of full dentures which are more stable during each phase of mastication.

The method of experimental design, we used, is versatile enough to allow the study of immersion in water at 37 degrees C during 15 days after curing, as a new parameter able to influence the deformation of denture bases, without any additional experiment. According to the experimental conditions used to make up denture bases, this parameter can, in some cases, modify appreciably the deviation in the palate region.

The investigation of means of recording mandibular movement has aroused the interest of a considerable number of researchers. Their own devices, increasingly ingenious, all display certain advantages and shortcomings. The need for a device more appropriate to the needs of day-to-day odontological use has been felt for some time. By giving a broad explanation of how it works, we have tried to assess the possibilities of the proposed prototype, the Cinetic. It measures movement of the dentalium in all three dimensions simultaneously. Since its reliability, when tested by a study concerning a sample of 40 patients, proved entirely satisfactory, a more sophisticated version was promptly devised. This latest Cinetic allows the ROZENCWEIG dyskinesia index, to be calculated, the FARRAR diagram to be drawn, and the mastication movements to be analysed by giving a visual display of the mandibular opening and closing trajectories, the speed diagram, the duration of the cycle, mandibular velocity and acceleration, and a breakdown of the cycles for each respective side. In order to be fully competitive, the Cinetic lacks the capacity to record and analyse condylar movement. Work on incorporating these features is currently at an experimental stage.

The development of devices to record the functional mandibular kinetics, has permitted the physiological analysis of the masticatory cycles. Therefore, it is possible to consider a functional integration of the corrections, by addition or subtraction to the occlusal surfaces of the teeth. For this purpose, we have established the conditions of a physiological concept of occlusion taking into account the efficiency of the masticatory apparatus through a velocity analysis. This is the N.M.C. concept or concept of Neuro-Muscular Compatibility. This concept has led us to define the ISCA (Intra-Cuspid Spatial Angle), represented by the angle defined in the three spatial planes, by the trajectory of the occlusal contact point of a cusp liding over its opposite, in any excursive opportunity. We have shortly reported the studies by Levin on the SIROGNATOGRAPH and the prospects resulting from these studies. Then, we have studied in greater details the Saphon VISI TRAINER III developed by HOBO and described the various potentials of its use in the GBM Laboratory in Vienna (France), with François DURET. We have also analyzed the specific points which seem to represent the weaknesses of this device and have outlined some solutions to this problem. This approach, within a clinical context, may at term give rise to a complex analyser-expert-system intends to facilitate the establishment of a reliable diagnosis and to control the physiological integration of our procedures. The establishment, at term, of parameters and constants of this function, will guide this progression towards success.

This study of the ceramicbutt joint in metal-ceramic prosthesis permits to compare three different laboratory procedures. With the results obtained with two reading processes (numerical measurement and direct measurement of image replicas of S.E.M. to evaluate the marginal gap, it is possible to confirm that: the gold foil method gives the thinnest gap (between 32.7 and 44.7 micrometers) with presence of overcontoured margins. The ceramicbutt joint made by duplicate method, in refractory material, proves to be larger (between 57 and 67.8 micrometers) with overhanging margins, and damaged by sandblasting. The direct elaboration method, on a plaster model, proves to be less precise (gap between 74.6 and 80.4 micrometers) with a round but glossy ceramic margins.

Located at the border between vestibule and palatine area, the retrotuberosity space plays a major role in full dentures, as it involves the lateral portion of the posterior palatine joint. The arrangement of the pterygo-maxillary complex determines the morphology of this space and its use in full prosthesis. In most cases, the pterygo-mandibular ligament originates at a distance of the tuberosity, leaving a small mucosal fold, posterior to the tuberosity. This element, often mistaken with the origin of the ligament, should neither be released at the prosthetic border, nor be considered as a negative index. On the contrary, the presence of compressible submucosal glandular tissue, could be used when the posterior joint is prepared.

When planning a fixed prosthesis, in some case it may be indicated to prepare a continuous ledge to be able to face a failure on one or several abutments. Thus, a partial denture can easily be adapted to the fixed bridge without major modifications. The continuous ledge will be covered with a cast continuous bar, intended to restore the lingual crown morphology. This continuous bar is waxed either directly on the fixed prosthesis, or on a duplicated model, the first way being more precise. This technique permits to protect the metal surfaces. The advantage of this procedure is obvious from a mechanical as well as an aesthetic standpoint.

A further study of the variance of deviation measurements of denture bases in the palate region shows that the variability of measurements is not essentially due to measuring, but also to the variability of denture processing. No more than the other previously studied parameters, the heating and cooling rates as well as the mode of insertion of resin in the cast have no effect on the dimensional accuracy of denture bases after curing.