Influence of resin cements and aging on the fracture resistance of IPS e.max press posterior crowns

The purpose of this study was to evaluate the effect of different adhesive cements and thermocycling on the fracture resistance of IPS e.max Press posterior single crowns. Thirty-two sound maxillary molars were subjected to standardized preparation and received IPS e.max Press crowns. Another 16 molars were left unprepared to serve as controls (group 1). Panavia F 2.0 and Rely X Unicem luting cements were used to bond the fabricated crowns (n = 16 each) to their respective prepared teeth. Eight specimens from each of the three groups were selected randomly for further thermocycling (5,000 cycles). All specimens were then subjected to fracture resistance testing using anatomical metal attachments fixed to the upper portion of the universal testing machine (1 mm/min). Data were analyzed statistically using two-way analysis of variance and the Student t test (α = .05). Natural teeth presented significantly higher (1,043 and 1,279 N) fracture resistance than that of adhesively cemented ceramic crowns (907 to 986 N) before and after thermocyling, respectively (P < .05). Cement type did not significantly affect fracture resistance results (986 N and 974 N for Panavia F 2.0 and Rely X Unicem, respectively; P > .05). Thermocycled specimens showed lower fracture resistance than that of nonthermocycled ones (P < .05). Neither conventional adhesive cement nor self-etching adhesive cement affected the fracture resistance of IPS e.max crowns. Thermocycling decreased the fracture strength of the crowns in both cement groups. Natural teeth fractured at significantly higher loads than the ceramic crowns.