By using scanning electron microscopy, the different crystals formed on basal crystals were observed in human dental calculus. In early calculus, polygonal column and triangular plate-shaped crystals of brushite or dicalcium phosphate dihydrate (DCPD) were formed on the mass of fine needle or sandygrain-shaped biological apatites (AP). In old calculus, elongated ribbon and plate-shaped crystals of octacalcium phosphate (OCP) were arranged on the glomerate structures of AP crystals; in addition, the alternation of these crystal layers were frequently observed. Hexahedrally based crystals of whitlockite (WH) were induced on the surfaces of OCP crystals and on the mass of AP crystals, while rod-shaped AP crystals were induced on the surfaces of WH crystals. Their appearances suggest that the epitaxial growth and transformation of DCPD, OCP, AP, and WH crystals easily occur in the microenvironment of dental calculus.
It is known that calcified deposits showing an aster-like structure on the sectioned and fractured surfaces are present in human supragingival calculus. In a tonsillolith collected from an old female, aster-shaped calcified deposits were also found. In both stones, the central regions showed a glomerate structure composed of fine needle or sandygrain-shaped crystals of biological apatites formed mainly by the extracellular calcification, and the marginal regions showed a radial arrangement of elongated ribbon and plate-shaped crystals of octacalcium phosphate. It is suggested that the deposits of the tonsillolith are formed in the sites surrounded with organic matter, and that the sites are similar to that of dental plaque where the deposits of dental calculus will be formed.
The effect of the Pd content in a powder alloy which was triturated with a commercial Ga-containing liquid alloy was evaluated by measuring its mechanical properties and by its clinical performance in class I restorations. Experimental powder alloys were prepared by reducing the Pd content of a commercial powder alloy, which contained 10 wt % Pd, to either 3 wt % or 0 wt % (Pd-free alloy). The clinical performance of the restorations was significantly improved by decreasing the Pd content to 3 wt %, and the degree of marginal integrity correlated with the creep. Therefore, these results suggest that the Pd content in the commercial alloy should be reduced to 3 wt % to improve its clinical longevity.
Changes in the contractile tension and muscle length of rat superficial masseter muscles were measured together with postnatal increases in body weight from the age of 3 to 11 weeks to establish control data during growth. Isolated masseter muscle fiber bundles were used for precise measurement of contractile tension and muscle length. Up to the age of 5 weeks, female rats showed a greater contractile tension than male rats. At the 6th weeks, the level of contractile tension in male and female rats was similar. The tension development curve in 6-to 9-week-old males was sigmoidal, while that in 6-to 8-week-old females showed a linear increase. Male and female rats reached maximum contractile tension at 9 and 8 weeks of age, respectively. The most remarkable changes in contractile tension from the age of 6 to 9 weeks correlated with rapid changes of body both weight and muscle length. Statistically significant relationships were observed between contractile tension and both body weight and muscle length. These findings suggest that the changes in the contractile tension were influenced by morphological changes as well as by individual growth. These findings will also be useful as control data regarding the rat superficial masseter muscle contractile tension.
Effects of manipulative variables such as the type and volume of chips in a barrel on the barrel polishing were examined. It was found that these significantly affected the amount of polishing and the surface texture of the workpiece. The highest amount of polishing was obtained when using RK chips which had an irregular shape. Then the surface roughness of the workpiece after polishing was about 1.5 μm Rmax. The smallest amount of polishing was obtained when using SA chips which had a spherical shape and wasn't good enough to form the smooth surface. The worst polishing efficiency was obtained at 80 vol % with all chips. Larger amounts of polishing were obtained when using RK chips and UP chips at 20 vol %. In this study, the best dimensional change and surface texture of the workpiece was produced by UP chips which had a columnar shape at 60 vol%.