Cuspal movement and gap formation in premolars restored with preheated resin composite

The current study aimed to determine the effect of preheating resin composite to three different temperatures on the cuspal movement and gap formation at the tooth/restoration interface.

Fifty extracted, sound human upper premolars were subjected to standardized MOD cavity preparations. Five groups of 10 premolars each were restored with either 1) Tetric Ceram HB, 2) a layer of Tetric Flow followed by Tetric Ceram HB, 3-5) preheated composite to 37 degrees C, 54 degrees C and 68 degrees C, respectively, using a chair-side preheating device (Calset thermal assist unit). Cuspal movement was calculated by measuring the intercuspal distance between the indexed cusp tips before restoration 5 minutes and 24 hours after composite curing using a stereomicroscope. The teeth were sectioned longitudinally and examined under a stereomicroscope connected to a digital camera and image analysis software to detect gap formation.

Group 2 showed the least cuspal movement at 5 minutes and 24 hours and the highest gap area, while Groups 4 and 5 showed the highest cuspal movement at 5 minutes and 24 hours. Group 3 had the least gap area.

Preheating resin composite to temperatures higher than 37 degrees C increases cuspal movement. The adaptation and gap area of preheated resin composite to 37 degrees C and 54 degrees C improved, but it did not change with resin composite preheated to 68 degrees C.