Fracture strength of all-ceramic crowns luted using two bonding methods

Statement of the problem. Excellent esthetic quality is one of the major advantages of all-ceramic restorations; however, catastrophic fracture of such restorations is still a disadvantage. Ceramic bonding systems using ceramic primers without the use of hydrofluoric acid have been introduced, but data about the efficiency of these systems are lacking. Purpose. This study investigated the influence of 2 bonding procedures on the fracture resistance of low-fusing ceramic and computer aided design-computer aided manufacturing (CAD-CAM) all-ceramic crowns. Material and methods. Forty-two standardized all-ceramic crowns were fabricated on human maxillary premolars. Seven unprepared maxillary premolars were used as control. Three all-ceramic crown systems were used: 1 low-fusing ceramic (Duceram) and 2 machineable ceramics (Vita Mark 11 and ProCAD) using the Cerec 3 CAD-CAM system. The intaglio surfaces of fabricated crowns (n = 7) were subjected to 2 different conditioning techniques: etching, using 4.9% hydrofluoric acid followed by application of Mirage ABC silane, or cleaning, using 65% phosphoric acid and application of primer (Porcelain Liner-M). The crowns were luted to the teeth using Superbond C&B luting agent. After 24 hours storage in water, specimens were loaded in a universal testing machine with the compressive load applied along the long axis of the specimen at a crosshead speed I mm/min until fracture. Fracture loads (N) were recorded. One-way analysis of variance (ANOVA) and the Tukey HSD test (alpha = .05) were used for statistical analysis of the data. Results. The mean fracture load of control specimens (738.3 +/- 195.3 N) was not significantly different from that of the 2 CAD-CAM crowns (667.7 +/- 72.3 N, 715.9 +/- 105.2 N). However, fracture load of natural teeth and the 2 CAD-CAIM crowns was significantly higher than the fracture load of the low-fusing ceramic crowns treated with HF acid and silane (465.5 +/- 101.1 N) and, when cleaned, using phosphoric acid and an application of primer (447.5 +/- 63.4 N) (P < .05). There was no significant difference in the mean fracture load of each ceramic material when bonded using the 2 different procedures, either treated with HF acid and silane or cleaned using phosphoric acid and application of primer (P > .05). Conclusion. The application of a primer (Procclain Liner-M) was an effective method for treating the intaglio surface of all-ceramic crowns before cementation.