Comparison of the shear bond strength of flowable composite materials in class V cavities under various conditions

Aim: The aim of this study was to compare dentin surfaces exposed to long-term gastric acid with those stored in artificial saliva and to evaluate the shear bond strength of different flowable composite resin materials. Material and Method: 80 caries-free human molars were used in this study. After embedding the teeth in acrylic blocks, the buccal surfaces were ground until dentin was exposed. Then polished using Sof-Lex disks in a standardized manner. Half of the specimens were subjected to an erosion cycle in a prepared gastric acid solution for 9 days, six times a day for 2 minutes each. The remaining specimens were stored in artificial saliva as the control group. For the application of flowable composites, silicone molds measuring 2.4 mm in diameter and 3 mm in height were adapted onto the dentin surface. The specimens were then divided into eight groups, each consisting of 10 teeth: Groups 1 and 5: Vertise Flow Self-Adhesive Flowable Composite (Kerr, Orange, CA, USA). Groups 2 and 6: Fusio™ Self-Adhesive Flowable Composite (Pentron Clinical, Orange, CA, USA). Groups 3 and 7: Estelite Universal Medium Flow (Tokuyama, Tokyo, Japan). Groups 4 and 8: EverX Flow (GC Corp., Tokyo, Japan). All materials were applied according to manufacturers' instructions. The specimens were stored in distilled water for 24 hours to complete post-polymerization. Shear bond strength testing was performed using a Universal Testing Machine (Autograph AGS-X, Shimadzu Corp., Kyoto, Japan). Failure modes were evaluated under a stereomicroscope at 30× magnification. To assess the effect of erosion on surface morphology, SEM images (Hitachi SU-1510, Japan) were obtained from randomly selected specimens. Statistical analyses were performed using SPSS software (IBM SPSS, IBM Corp., Armonk, NY, USA), with a significance level set at p < 0.05. Results: No statistically significant difference in bond strength was detected for Estelite Universal Medium Flow and Vertise Flow under erosive conditions. Conversely, EverX Flow™ and Fusio™ Self-Adhesive demonstrated increased bond strength in the presence of erosion. However, in both experimental conditions, self-adhesive materials exhibited significantly lower bond strength compared with conventional flowable composites (p < 0.05). Adhesive failure was the predominant failure mode, observed in 77 out of 80 specimens. Conclusions: This study suggest that EverX Flow™ and Fusio™ Self-Adhesive flowable composites may exhibit higher bond strength in clinical scenarios involving gastric acid–induced dental erosion. Although self-adhesive composites offer the advantage of reducing clinical steps, their overall bond strengths appear to be lower compared with conventional flowable composites. Keywords: Gastric Acid, Erosion, Self-Adhesive, Flowable Composite, Shear Bond