Effect of mechanical surface pretreatment, acid conditioning, and adhesive strategy on the repair microtensile bond strength of hydrolytically aged short fiber-reinforced resin composite: an in vitro study

Objectives: To evaluate the effect of different mechanical surface pretreatment methods, acid conditioning protocols, and adhesive strategies on the repair microtensile bond strength (µTBS) and failure-mode distribution of hydrolytically aged short fiber-reinforced resin composite (SFRC). Materials and methods: A total of 144 SFRC specimens were hydrolytically aged in artificial saliva for 3 months and randomly allocated to 12 experimental groups (n = 12) according to mechanical surface pretreatment (air abrasion or diamond bur roughening), acid conditioning (37% phosphoric acid or 9.5% hydrofluoric acid), and adhesive strategy (universal adhesive only, silane + universal adhesive, or Acid Resistant Silane [ARS]-containing adhesive). Following the repair procedures, beam-shaped specimens were subjected to µTBS testing and stereomicroscopic failure-mode analysis. Data were analyzed using three-way factorial ANOVA to evaluate the main effects and interactions of mechanical surface pretreatment, acid conditioning, adhesive strategy on µTBS, followed by Tukey’s post-hoc test for pairwise comparisons. Failure-mode data were summarized at the composite-disc level and analyzed using the Monte Carlo permutation chi-square test. Results: Three-way factorial ANOVA demonstrated significant main effects of acid conditioning and adhesive strategy (both p < 0.001), whereas the main effect of mechanical surface pretreatment was not significant (p = 0.100). Significant two-way interactions were observed between the treatment factors, whereas the three-way interaction was not significant (p = 0.644). The Air abrasion + Phosphoric acid + Universal adhesive protocol demonstrated the highest µTBS value (46.87 ± 4.44 MPa) and predominantly cohesive failures. In contrast, hydrofluoric acid-treated protocols demonstrated significantly lower µTBS values and predominantly adhesive failures. Additional silane application and use of an ARS-containing adhesive did not significantly improve repair bond strength. Conclusions: A simplified repair protocol combining mechanical surface pretreatment, phosphoric acid conditioning, and universal adhesive application provided favorable repair performance for aged SFRC. Hydrofluoric acid conditioning was associated with lower repair bond strength, while neither additional silanization nor the use of an ARS-containing adhesive provided a significant bond-strength advantage. Clinical relevance: Simplifying the repair procedure may reduce the number of clinical steps and associated technique sensitivity, potentially facilitating chairside repair of aged SFRC restorations.