The Influence of Retention Holes in Porcelain Teeth on Retentive Force and Impact Strength

Abstract

The purpose of this investigation is to determine what are the diatoric forms of the posterior porcelain tooth possessing both sufficient toughness for impact and retentiveness to denture materials.In this article, an experiment with 10 types 27 sets of home-made artificial porcelain teeth (molars and premolars) consists of(1) the observation of the ratio of the diatoric form's area (SII) to the ridge lap surfaces of teeth (SI), the ratio SII/SI.(2) In the retention hole on the cross-sectional area of the porcelain tooth, the measurements of the height, the width, the undercut wells of them and the angle of intersection between the axis of crown and that of the retention hole.(3) tensile test.(4) repetitive impact test in distilled water at 37±1°C.The specimens for the both test were made by planting a porcelain tooth in a resin-block along the axis of crown and then were immersed in distilled water at 18°±2°C.Through these experiments, the following results were obtained.The ratio SII/SI was not constant in all types and molds. Preferably there was a tendency that the larger the crowns became, the smaller ratio SII/SI became. The height, the width and the undercut wells had similarly no relation. But the angle of inclination was closely resemble every molars and premolars regardless of upper or low teeth, and the premolars were higher than the molars.Conserning with the tensile strength, each porcelain tooth was as follow: 5, 8.5±2.1kg; 5, 8.6±2.5kg; 6, 11.4±2.7kg ;6, 11.6±2.8kg; on each mean, which indicated that the molars were always higher than the premolars although there was no constant relation with every mold. The tensile strength was affected by the diatoric designs, upon which not only the depth of the undercut wells but the height, the width, and the angle of inclination had seemingly great influence.After the test, fractures of the porcelain were left on the resin-blocks in the case of the specimens with high strength.As to the impact test, about the half of specimens were satisfactory. The rest of them were broken preceding 4000 strokes. Among them, the relation could be found in the molars that the number of the upper teeth broken was more than the low, but in the premolars could not.An important characteristics of this test was the effect of the air vent holes in mesio and distal surface of the porcelain teeth.The porcelain teeth with them generally had lower impact strength, and their crack (by the impact) always went through the air vent holes, which had frequently been seen in a clinic.Therefore the question was raised whether they were necessary.