Effects of cavity form and setting expansion of refractory dies on adaptability of Class II (MO and MOD) fired ceramic inlays

This study investigated the effects of cavity divergence and setting expansion of refractory die material on the adaptability of Class II (MO and MOD) fired ceramic inlays. Standardized Class II (MO and MOD) cavities with two kinds of lateral wall divergence (10 and 20 degrees) were prepared in epoxy resin blocks. A refractory die was prepared from an impression of the epoxy resin cavity in which the setting expansion ranged from 0.04 to 1.14%. 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 indicate that the setting expansion of the refractory die materials and the divergence of the lateral walls had significant effects on the adaptability of Class II (MO and MOD) fired ceramic inlays. The inlays fabricated on the refractory dies with small setting expansion showed small internal gaps in Class II (MO) cavities. Significantly good adaptation was achieved when the setting expansion was 0.32% or less (p < 0.05). The inlays fabricated on the refractory dies with large setting expansion showed small internal gaps in Class II (MOD) cavities. Significantly good adaptation was achieved when the setting expansion was 0.87% and greater (p < 0.05).