Bond Strength of Injectable Composites Under Different Enamel Treatments and Bonding Strategies

OBJECTIVE: The effectiveness of enamel acid etching may be enhanced when combined with additional surface treatments, such as diamond bur grinding. However, there are no reports of the effect of enamel grinding and bonding strategies when a universal adhesive and highly filled flowable composites are used. The aim was to evaluate the effect of enamel grinding and adhesive strategy on the microshear bond strength (micro-SBS) of injectable composite resins. MATERIALS AND METHODS: One hundred sixty enamel specimens were randomly allocated into 16 groups according to enamel preparation (diamond bur grinding or no grinding), adhesive strategy (self-etch or etch-and-rinse), and composite type (three injectable composites and one conventional composite). After 48 h of water storage, the specimens were tested for micro-SBS in a universal testing machine (0.5 mm/min). Data were analyzed using three-way ANOVA and Tukey's test for micro-SBS data, and Fisher's exact test and Chi-square test for failure mode (α = 0.05). RESULTS: A significant main effect was observed for bonding strategy (p < 0.001), but not for enamel preparation (p = 0.042) and composite resin (p = 0.044). The etch-and-rinse strategy resulted in significantly higher bond strength than the self-etch approach, irrespective of the enamel preparation, for all the resin composites (p < 0.05). Adhesive strategy was the most frequent mode of failure (35%), with self-etching yielding a 70% rate of adhesive failures compared to 0% for the etch-and-rinse approach. CONCLUSIONS: The etch-and-rinse strategy improved enamel bond strength and eliminated adhesive failures for all composites tested, regardless of enamel grinding. CLINICAL SIGNIFICANCE: Enamel should be etched before applying a universal adhesive for injectable composite restorations, as this increased bond strength and eliminated adhesive failures regardless of enamel grinding or composite type. Diamond bur grinding only reduced adhesive failures when the self-etch mode was used.