Effect of cavity form and setting expansion of refractory dies on adaptability of fired ceramic inlays

The purpose of this study was to investigate the effect of cavity form and setting expansion of refractory die materials on the adaptability of fired ceramic inlays. Standardized Class I cavities with three kinds of lateral wall divergences (10 degrees, 20 degrees, and 30 degrees) and three kinds of surface roughness were prepared in epoxy resin blocks. A refractory die was prepared from an impression of the epoxy resin cavity, whose setting expansion ranged from 0.01 to 1.13%. A ceramic inlay was fired on each die. The fabricated inlay was inserted into the epoxy resin cavity, and the interfacial distance between the ceramic inlay and the cavity wall at the margin was measured using a reflecting microscope at X100 magnification. The internal fit was measured after sectioning the specimen longitudinally. The results were analyzed by ANOVA and Sheffé's F test. Good adaptation was achieved with the smooth-surface cavity. The adaptability depended on the angle of the cavity divergence, and small gaps were observed in 20 degrees and 30 degrees cavities (P < 0.05). The inlays fabricated on the refractory dies with a small setting expansion demonstrated small internal gaps. Significantly good adaptation was achieved when the setting expansion was less than 0.2% (P < 0.05). The results indicated that the cavity form and the setting expansion of the refractory die material had significant effects on the adaptability of fired ceramic inlays.