Fracture resistance of human teeth in different types of cavity preparation with sharp and rounded internal angles

This work was carried out on three types of cavities : 1.Class [I] conservative cavities were prepared in 40 molars, these cavities were then divided into three groups : A. Group [1] : Constituted of 20 class [I] cavities that were prepared in ten upper molars and ten lower molars where five upper and five lower cavities were prepared with rounded internal line angles. The other teeth were prepared with sharp internal line angles. B. Group [2]: Constituted of the remaining 20 class [I] cavities that were filled with non-gamma 2 amalgam in the same number of cavities and in the same number of teeth as in group [1] 2. Class [II] conservative cavities were prepared in the same number of teeth [molars], the teeth were classified similar to that of class [I]. 3. MOD conservative cavities were also prepared. The teeth were also classified similar to that of class [I] and class II. A compressive force was applied to fracture each tooth by the Instrom Universal Testing Machine. It was found that: 1. No significant difference in the fracture resistance of sharp versus rounded line angles, preparations in the filled and unfilled teeth with amalgam. 2. There was a significant difference between filled and unfilled teeth that cause fracture of teeth prepared with conservative preparations rather than those filled with gamma 2 amalgam. 3. There was a significant difference in the fracture resistance between simple cavities [Class I] and compound cavities [Class II] or complex types [MOD Cavities]

Evaluation of porcelain surface after glazing by diamond polishing paste

30 vacuum fired [Vita] porcelain discs [10 mm. In diameter were prepared under identical conditions. All the specimens were finished to smooth surface and divided into three groups no. one glazed with natural glaze, the second with low fusing glazing paste, and the third glazezd with diamond polishing paste. Comparisons were evaluated by means of [surtronic] tracer. The mean surface roughness, obtained by the diamond poliching paste, was less than natural glaze. The difference was not significant at 5% level. The mean surface roughness, obtained by the diamond poliching paste, was less than the low fusing glazng paste, the difference was significant at 5% level. From this study, it is concluded that: 1- Glazing of vacuum fired porcelain can be achieved by polishing paste. 2- After spot grinding of porcelain, resmoothing and reglazing the surface can be achieved without exposing the porcelain and the underlying metal to a more further firing. Agreement with Barghi et al [1976][3] who found that the vacuum fired porcelain is less porous than air fired porcelain