Bond strength of different viscosities Giomer-based composites to dentin under erosive conditions

The present study aimed to evaluate the bond strength of Giomer-based restorative composites with different viscosities bonded to dentin under various erosive conditions.

One hundred and twenty dentin specimens from human sound molars were selected and divided into three groups according to the erosive challenge: ERO (initial erosion with citric acid 0.3%, pH 2.6, 5 min, 5x/day, 1 day), CYC (ERO protocol, followed by an additional 5-day erosive cycling challenge after restoration), and CON (sound dentin, without erosion, control). Specimens were further subdivided into four groups (n = 10) according to the Giomer-based restorative material used: flowable composite (FC), flowable bulk-fill composite (FBF), regular-viscosity composite (CC), and regular-viscosity bulk-fill composite (CBF). Two cylinders (1.5 mm diameter) with the resins from each group were made in each sample, after applying the two-step self-etching adhesive system. In the CYC group, the erosive cycle was carried out before and after placement of the adhesive system and composite cylinders. Bond strength was assessed by the micro shear test, and failure was quantified in a stereomicroscope. The data were submitted to two-way ANOVA, followed by the Tukey test (p < 0.05).

Significant differences were observed for the eroded substrate (p = 0.010) and the composite resins (p = 0.037), but not for their interaction (p = 0.677). The CYC groups showed lower bond strength values than control group, and only the FC composite presented lower values than FBF, while CC and CBF showed similar values.

Erosive cycling decreased the bond strength for all composites tested, irrespective of their viscosity. Regarding the flowable composites, the bulk fill one presented a higher value than the conventional non-bulk fill, while this difference was not observed for the regular-viscosity composites.