歯科用陶材の粒子の移動が色調に及ぼす影響

抄録

Ceramo-metal restorations are widely used because of their superiorities in esthetics, biocompatibility, toughness, and resistance to chemical attack. However, the dental professionals have long been concerned with the problem of a difficulty in harmonizing the color of ceramo-metal restorations with that of the patient's natural dentition. The purpose of this study was to confirm the mutual migration of the enamel and dentin porcelain particles during condensation process and its effects on the color changes of the ceramo-metal restorations. The porcelain slurry was condensed with four kinds of condensers : experimental condenser utilizing a revolving pulley (EC), Le Cron carver (LC), ultrasonic condenser (UC), ultrasonic condenser combined with hot air (UH). The migration of the enamel particles through the enamel-dentin interface during condensation was estimated by the penetration of the fluorescent particles contained in the enamel powder into the underlying dentin layer, which was detected with an epifluorescence microscope. Among the condensers used, EC exhibited the maximum penetration distance of the enamel particles and UH the minimum. For color analysis, dentin and enamel layers were built up in several different proportions of thickness so as to be 1.2mm thick in total. The porcelain was fired by two-different procedures : one-step firing technique in which the molded dentin and enamel were fired simultaneously, and two-step technique in which the dentin was molded and fired first and then the enamel was molded and fired. The enamel particles, therefore, could penetrate into the dentin layer in the one-step technique but not in the two-step technique. By comparing the ceramo-metal specimens fired by these two techniques, it was found that their colors were affected by the particle migration. The values of luminous reflectance and chromaticity coordinates were significantly increased with the particle migration when EC, LC, or UC causing larger migration were used. In the case of UH showing smallest particle migration, the luminous reflectance was also increased but the chromaticity coordinates were not significantly changed by the migration. This indicates that the luminous reflectance may be more markedly affected than the chromaticity coordinates by the particle migration. Color differences also appeared in the range of "trace" or "slight", although a definite relationship between the color difference and the particle migration could not be recognized.