抄録
The purpose of this pilot study was to examine the optimal conditions for the best denture design among ordinal distal extension removable partial denture without soft liners (design Ct : Control), distal exension ones with teeth which are used by "sandwiching" a resilient silicone layer between the basal seat of dental teeth and the resin base of the denture (design E-type), and distal extension ones with ordinal soft liner over the basal seat of the denture (design R-type), by analyzing their displacement of the abutment tooth under loads. A sheet shaped test food was placed on the lower left second premolar, first and second artificial molars of Kennedy class II, and the movement of the abutment tooth (〓) was measured by using digital laser displacement sensors and the measured values were reciprocally compared through the statistical analysis. The results obtained were as follows : 1) Parallel movements were generally largest in all designs, and inclinations, depressions, and twist-like movements became smaller in the descending order. Especially the amount of parallel movement in design R-type was very large, 1.5 to 3 times that of inclination. 2) As compared with design Ct, the parallel movement was larger in all designs of R-type, and the inclination was smaller in all designs of E-type. Except for a part of parallel movements, all of abutment tooth displacements in E-type which has resilient soft layer of 1.5 mm thickness were smaller than in each one of Ct. 3) As the thickness increases from 0.5 mm (R1), to 1.0 mm (R2) and 1.5 mm (R3), the amount of parallel movement, depression and inclination in R-type remarkablly increased. In E-type, however, the displacement amount conversely decreased as the thickness increases from 0.5 mm (E1) to 1.5 mm (E3), and differrential findings in the displacement were recognized only in design E2. 4) The buccolingual displacement of denture plate in design E-type was also larger than that of design R-type. On the basis of the foregoing findings, the method of relining with soft liners over the basal seat of the denture was confirmed to be improper for the distal extension removable partial dentures, because this method increased the amount of inclination which is said to cause the most hazard to the health of the periodontal tissues. The inclination, however, was not brought about by the depressive difference between periodontal membrane of the abutment tooth and resiliant tissues under the denture base, as generally believed, but this displacement was considered to be significantly associated with the buccolingual movement of the denture plate and succeeding parallel movements of the abutment tooth. Althoug some problems still remain for the denture with teeth utilizing soft layer, this method seems to be an effective one because it has a highly inhibitory action against the occurrence of inclination including the denture displacement.
