Influence of various bonding techniques on the fracture strength of thin CAD/CAM-fabricated occlusal glass-ceramic veneers

Objectives: To evaluate the efficiency of immediate dentin sealing and the effects of different bonding protocols on the fracture strength of CAD/CAM occlusal veneers bonded to exposed dentin. Methods: Ninety-six extracted maxillary premolars were initially divided into three main groups with 32 specimens each: without immediate dentin sealing, immediate dentin sealing/total etching and immediate dentin sealing/selective etching. Teeth were identically prepared in the dentin to receive occlusal veneers of 0.8 mm thickness, milled from lithium disilicate ceramic blocks (IPS e.max CAD). Each main group was later subdivided, according to the pre-cementation surface etching protocol (total/selective), into two subgroups with 16 specimens each. All restorations were adhesively bonded using a resin cement (Variolink Esthetic). Half of the specimens of each subgroup were subjected to thermo-dynamic loading in a chewing simulator with 1,200,000 cycles at 10 kg load. The other half and the surviving specimens were subjected to quasi-static loading until failure. Statistical analysis was performed using three-way ANOVA and Tukey's post-hoc tests. Results: All specimens except one survived the artificial aging. A significantly higher fracture strength of restorations (p <= 0.001) was obtained when immediate dentin sealing was followed regardless of the etching method with values ranging from a minimum of 1122 +/- 336 N to a maximum of 1853 +/- 333 N. Neither the pre-cementation treatment nor the artificial aging had a statistical significant effect on the fracture strength. Significance: Immediate dentin sealing protocol is recommended whenever dentin is exposed during the preparation for thin glass-ceramic occlusal veneers.