Influence of cementation technique on fracture strength and leakage of alumina all-ceramic crowns after cyclic loading

Objective: To compare in vitro the influence of 3 cementation techniques on leakage and fracture strength of alumina all-ceramic crowns after cyclic loading in an artificial chewing simulator. Method and Materials: Forty-eight extracted molars were mounted in a way that simulates natural tooth mobility. Crowns (Procera Alumina, Nobel Biocare) were fabricated and inserted with either conventional cementation with zinc phosphate cement without pretreatment (group ZOP); cementation with a universal adhesive resin cement without pretreatment (group HYB); or adhesive bonding with composite resin after pretreatment of the tooth (dentin bonding agent) and the crown (airborne-particle abrasion and a special ceramic priming agent containing adhesive monomers that bond to metal-oxide ceramics) (group ADH). All specimens were stored in artificial saliva and subjected to 1.2 million load cycles in a dual-axis chewing simulator (Willytec). Eight specimens per group were subjected to compressive load until failure, while the remaining 8 specimens were stained and sectioned for measuring of dye penetration. One-way ANOVA and Tukey HSD were used for statistical analyses (a = .05). Results: Cementation techniques were significantly different (P = .009) in regard to mean load at failure. Fracture strength was significantly greater for ADH (mean load at fracture, 2,782 ± 419 N) as compared to HYB (1,980 ± 270 N) or ZOP (1,788 ± 242 N). All groups differed significantly for leakage values (P .001), with ADH showing the lowest mean leakage (0.04 ± 0.07 mm), followed by HYB (0.96 ± 0.16 mm) and ZOP (2.44 ± 0.19 mm). Conclusion: Cementation technique affects fracture strength and leakage of all-ceramic molar crowns. Fracture strengths were well above natural chewing forces for all cementation methods. However, adhesive bonding significantly increased fracture strength and improved marginal seal of alumina crowns. Parole chiave: all-ceramic, alumina crown, cementation, fracture strength, marginal leakage