The influence of luting cement on the probabilities of survival and modes of failure of cast full-coverage crowns

Objectives. This study compares the probabilities of survival and modes of failure of cast full-coverage crowns bonded with five cements when subjected to tensile pull-off testing. Methods. Five groups of 25 sound human premolar teeth wen prepared for full-coverage crowns, impressions recorded and customized castings fabricated in Ni-Cr-Mb bonding alloy. The cements tested were zinc phosphate, a hand-mixed and capsulated conventional glass-ionomer cement, a resin-modified glass-ionomer cement and a resin composite luting cement. The cemented crowns were stared in water at 37 degrees C for 24 h prior to application of a tensile pull-off force at a strain rate of 10 mm/min. The loads at failure were ranked and modelled by derived Weibull functions each describing the probability of a given specimen failing under a given load. Non-parametric statistical analysis was also applied to the results. Results. There were no significant differences between the loads at failure of zinc phosphate cement, the hand-mixed or the capsulated glass-ionomer cements. The resin-modified glass-ionomer cement and the resin composite cement failed at significantly higher loads than the other three cements, but were not significantly different from each other. The Weibull modulus ranking for each cement from highest to lowest was resin composite = zinc phosphate, resin-modified glass-ionomer, hand-mixed conventional glass-ionomer and capsulated conventional glass-ionomer cement. Significance. Weibull analysis allows dentists to compare the probability of survival of a crown bonded with different cements at a chosen load giving an indication of cement reliability. (C) 2000 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.