Crack formation of all-ceramic crowns dependent on different core build-upand luting materials

Objectives: The aim of this in vitro study was to evaluate various core bui ld-up and luting materials regarding their effect on crack formation of all -ceramic crowns. Methods: Fifty-six freshly extracted sound human third molars were prepared according to a standardized procedure obtaining a circular shoulder of 1.5 mm with all margins located in dentin. Sixty percent of the dentin volume were removed and restored with totally bonded build-up composite resins or resin-modified glass ionomer cements (RMGIC) or compomers. Cast IPS-Empress caps were manufactured and luted with the different materials. For each ma terial group, the volumes of the core build-ups and of the luting cements w ere determined. The caps were examined for cracks after 1, 3, 6, 9 and 12 m onths storage in 0.9% saline solution at 37 degrees C. Results: The tested groups revealed no major differences in the percentage of the core build-ups and in the volume of the luting cements. After 12 mon ths only the group with composite resin build-up and luting showed no crack formation. RMGIC/compomer build-up or RMGIC/compomer luting always resulte d in cracking of the caps. Conclusions: Within the limits of this study it can be concluded that the h ygroscopic expansion of RMGIC/compomer materials led to failure of all-cera mic crowns, when the materials are used for both core build-up or adhesive bonding. (C) 1999 Elsevier Science Ltd. All rights reserved.