Efeito do tempo de aplicação de ácido fluorídrico na resistência de união de duas vitro cerâmicas ao cimento resinoso

Abstract

The objective of the study is to evaluate the influence of different times of application of 10% hydrofluoric acid on a glass-ceramic of lithium disilicate (LD) and a glass-ceramic of lithium silicate containing zirconia (LPD) on the bond strength to the resin cement. Glass-ceramic blocks were sectioned transversely and polished to obtain samples (n = 30). Composite resin samples (n = 30) obtained using a silicone matrix. The samples were randomly divided into 3 experimental groups (n = 10), according to the conditioning time (20 s, 40 s and 60 s): LPS20, LPS40, LPS60, LD20, LD40 and LD60). Hydrofluoric acid was applied to the cementation surface of the ceramic sample for the time determined for the group and removed with air-water jets, followed by a sonic bath for 480 s. After drying, the silane was applied to the conditioned surface of the ceramic and cementation of the resin sample, waiting 60 s. Afterwards, the resin cement was applied on the surface of the resin. The ceramic was positioned on the cement, under a load of 750 g and photoactivated. The set was sectioned in a cutter to obtain specimens (PCs). The CPs were subdivided into two groups: half for immediate testing and the other half for testing after 3 months of storage in water at 36°C. The CPs were joined to a device in a universal testing machine and subjected to traction force until fracture. The maximum fracture load (in N) was recorded and the bond strength (MPa) calculated. Bond strength data were analyzed by Kruskal-Wallis and Tukey. The acid etching time and storage showed influence on the bond strength of LD and LSP to the composite resin. The conditioning time of 20 s is suitable for both glass ceramics. For LD, the bond strength provided by 40 s and 60 s of conditioning was lower than by 20 s. Although LPS showed similar immediate bond strength between groups, the time of 20 and 60 s showed better results after aging. The acid etching time of 20 seconds is adequate for the two glass ceramics, being critical for the LD.