Retention of CAD/CAM resin composite crowns following different bonding protocols

To evaluate the effect of different surface treatments and primers with a CAD/CAM resin composite block on its crown retention.

120 human molars were prepared with a 24° total convergence angle, 1.5 mm height, and axial walls in dentin. Surface area was measured by digital microscopy. Crowns were machined from CAD/CAM resin composite blocks. Teeth were randomly allocated to 12 groups (n= 10) based on possible combinations of three surface treatments: [Control, Alumina air abrasion (50-µm Al₂O₃ at 0.28 MPa) ]; 5% hydrofluoric acid etch (20-second scrub); silane application (with or without Kerr Silane primer); and adhesive application (with or without Optibond XTR Adhesive). Optibond XTR Adhesive was applied to the tooth preparations and crowns were bonded with MaxCem Elite cement. Crowns were fatigued for 100,000 cycles at 100 N in water and debonded in tension (1 mm/minute). Crown retention strength (maximum load/surface area) values were analyzed using a three-way ANOVA with Tukey's post-hoc tests (α= 0.05).

Surface treatment, silane and adhesive applications independently affect retention force (P< 0.05). All interactions were not significant (P> 0.05). Alumina airborne abrasion surface treatment, silane and adhesive applications all improve retention strength. Therefore, CAD/CAM resin composite crowns can withstand debonding while undergoing mechanical fatigue. Although all forms of surface treatment and primer application improve bond strength, the highest mean retention strength values were recorded when the crowns were alumina particle abraded and coated with adhesive (with or without silane).

In order to improve the bonding of resin composite crowns, application of alumina airborne particle abrasion and a coat of adhesive (proceeded by an optional coat of silane) is recommended. If hydrofluoric acid is utilized, the crowns should be treated with a coat of silane followed by adhesive application.