Effect of 'Try-in' paste removal method on bond strength to lithium disilicate ceramic.

Objectives: The aim of this study was to evaluate four methods of Try-in paste removal from a lithium disilicate ceramic surface before cementation and assess the influence on bond strength to a resin luting cement.

Methods: Slices of dentine (1.6mm thick) were sectioned from the crown of human third molars and truncated cone shape cavities were made with diamond burs. IPS e.max Press ceramic blocks were obtained for each cavity, etched with hydrofluoric acid and fixed with temporary paste, except for Group G1, which was cemented according to the manufacturer's instructions. Try-in paste was removed from the experimental groups using different techniques: G2, ultrasonic bath in distilled water (5 min); G3, air/water spray (1 min); G4, etched with phosphoric acid (2 min)+air/water spray (30 s) and G5, etched with phosphoric acid before and after hydrofluoric acid application+air/water spray (30s). The ceramic restorations were cemented with the same procedures as G1. Push-out bond strength testing (MPa) was performed in a universal testing machine with a crosshead speed of 0.5mm/min.

Results: One way ANOVA and Tukey's test (P<0.05) were applied: G4(19.21)a, G2(17.09)ab, G1(16.82)ab, G3(16.18)ab and G5(15.9)b. The results showed that all of the experimental groups showed remaining particles of Try-in paste. The bond strength in G4 was statistically higher than in G5. No significant difference was shown in the other groups. There was a predominance of adhesive failures between resin cements and ceramics in G5.

Conclusion: The techniques used were not totally effective at removing the Try-in paste; however, the presence of remaining material did not influence the bond strength of restorations. The methods of temporary paste removal may affect the bond strength of ceramic restorations.