Effect of different labio-lingual spaces in tray designs on the displacement of and pressure against a mobile tooth.

The present study aimed to examine the effect of custom tray designs on the displacement of mobile tooth and local impression pressures during the impression procedure, using partially edentulous simulation models with six anterior teeth containing a mobile tooth prepared in previous studies. The custom trays were designed by altering the thickness of the respective spaces on the labial and lingual sides of the remaining tooth arch. In previous studies, the mobile tooth was displaced in the labial direction and local impression pressures of the mobile tooth were greater against the lingual side than the labial side for all custom tray designs. Furthermore, the custom trays perforated with holes on the lingual side were effective to reduce mobile tooth displacement, labial and lingual impression pressures against the mobile tooth, and the differences between them. Therefore, the present study was performed focusing on the labial and lingual thickness of spaces in custom tray designs. It was found that mobile tooth displacement, labial and lingual impression pressures against the mobile teeth and their differences were less in trays with spaces>3.0 mm thick on both the labial and lingual sides, but markedly greater in trays with a 1.5 mm-thick space on the labial side. These results indicate that the thickness of spaces on the labial side in the tray should not be reduced to prevent mobile tooth displacement.

Influence of lip support on the soft-tissue profile of complete denture wearers.

Complete dentures change the soft-tissue profile, although the exact relationship remains unclear. This study examined the relationship between the presence and degree of lip support provided by dentures and the lateral views of the facial appearance of edentulous patients. The subjects were five edentulous patients (three men and two women). Their facial appearances with experimental record blocks, with and without their complete dentures, were measured using a three-dimensional laser measuring system. The experimental record block for each subject had different conditions in the anteroposterior direction anteriorly but the same vertical dimensions posteriorly. The lateral digital facial images were displayed on a computer monitor, and the linear and angular measurements were analysed using image analysis software. The nasolabial angle was smaller and the labial points projected more with excessive lip support versus with deficient support. Moreover, the counter of the nose was affected by the labial flange of the record base, particularly in the facial appearance of one subject with highly atrophic residual ridges. The lip support affected the lower facial soft-tissue profile, including the lower part of the nose; the nasolabial angle and positional relationship between the lips and Ricketts's esthetic plane (E plane) are useful indexes for examining lip support.

Analysis of residual ridges and ridge relationship by three-dimensional reconstruction method.

The purpose of this study was to develop a diagnostic system with which to determine the adequate area for artificial tooth arrangement on the posterior residual ridge. Edentulous plaster models and occlusion rims were measured by a non-contact type shape measurement system. Three trigonal pyramids and their impressions on the occlusion rims were used as landmarks for the analysis and superimposition of the analysis results for the upper and lower ridges. The data points were obtained at intervals of 0.5 mm in the lateral direction and of 0.25 mm in the anteroposterior direction, and were interpolated by cubic spline curves in the lateral direction. When the ridge contour of the reconstructed image came in contact with the tangent line inclined at 30 degrees to the tentative plane of occlusion at the buccal and lingual sides in the frontal section, the area between their points of contact on both sides was comparatively flat and was regarded as adequate for the artificial posterior tooth arrangement in this study. This diagnostic system seems to be useful in determining the adequate area for the artificial tooth arrangement on the posterior residual ridges of edentulous plaster models and in displaying their horizontal relationship.

A visual method for analysing bucco-lingual position of artificial posterior teeth. Part 1: use of the ridge crest.

We have developed a visual analysis method to examine the spatial relationship between the edentulous ridges and the bucco-lingual position of the artificial posterior teeth in complete denture fabrication. In this system, a non-contact type shape measurement system is used. We applied this system to the plaster models and the wax dentures of an edentulous patient. Using the measurement data on the upper and lower plaster models, we reconstructed their shape three-dimensionally and determined the points regarded as the ridge crests and the inter-alveolar crest lines in the frontal sections. To generate the upper and lower ridge crest lines which consisted of the points of the ridge crests, interpolation by B-spline curves was applied. Furthermore, the loft surfaces that we regarded as the consecutive inter-alveolar crest lines, were generated between the upper and lower ridge crest lines. The surface models of the plaster models and artificial teeth were displayed on the cathode-ray tube display unit, and the ridge crest lines and the consecutive inter-alveolar crest lines were superimposed on the surface models. This method could be utilized to visualize and examine the bucco-lingual position of the artificial posterior teeth in reference to the inter-alveolar crest lines.

Application of a three-dimensional reconstruction method to analysis of the residual ridge.

The purpose of this study was to develop a new method of analysing the shape of the residual ridge. The line of the residual ridge crest was regarded as the reference for artificial tooth arrangement and a method of determining it was evaluated. The shape of a plaster model was measured with a contact-type shape measurement system. The measurement data in each frontal section were interpolated by cubic splines. The points corresponding to the residual ridge crest were calculated and superimposed onto the image of the plaster model on a monitor screen of an image processor. Using these points and the image of the plaster model, the line of the residual ridge crest was marked on the plaster model. It was concluded that this method could be used to determine the line of the residual ridge crest on a plaster model.

[A consideration of determining the removal or retention of teeth in the patient with a few remained teeth].

The alveolar bone of edentulous ridge is resorbed after the teeth extraction and the subsequent denture insertion. For the periodontal structure, the stress transmitted along the longitudinal axis is favorable, but the horizontal stress is destructive. Under the overdenture application which the retained teeth have the reduced clinical crown, it is possible to prevent the alveolar bone resorption and to improve the involved teeth. However it is difficult for the inclined teeth to get the successful results. In a case, having a few remained teeth contained the embedded root stump and the overdenture being applicated, we obtained the suggestion as follows. 1. Also the embedded root stump is useful to prevent the alveolar bone resorption. 2. The top and direction of longitudinal axes of the inclined abutment teeth can be determined by means of surveying the least teeth movement when the stress was applied to the teeth by the fingers with dental pincette. 3. Also to the inclined abutment teeth, it is possible to transmit the stress along the longitudinal axes, when the overdenture has the contact with the short dome coping at the top and in the inferior area to the longitudinal axes inclined, and is relieved in the superior area to its axes.