A Novel Approach to Improve Repair Bond Strength of Repaired Acrylic Resin: An in Vitro Study on the Shear Bond Strength

Purpose: To evaluate the combined effect of mechanical surface treatment with intermediate bonding agents (methyl methacrylate [MMA] and silane coupling agents) and ZrO₂ nanoparticle (nano-ZrO₂ ) addition to repair material on the shear bond strength (SBS) of repaired denture bases.

Materials and methods: Heat-polymerized acrylic resin was used to fabricate 130 cylindrical blocks (15 mm × 10 mm) and divided into a control group without treatment (C, n = 10), and 3 repair groups (n = 40/group) divided into specimens treated with alumina blasting alone (AB), specimens blasted with alumina combined with silane coupling agent (AB + SCA), or combined with MMA-based composite bonding agent (AB + MA). Treated groups were further subdivided according to nano-ZrO₂ concentrations into 0 wt%, 2.5 wt%, 5 wt%, and 7.5 wt% added to repair resin powder. Repair resin monomer and polymer were combined and packed on the repair area and then placed in a pressure pot at 37°C for 15 minutes for polymerization. Shear bond test was performed using a universal testing machine. Scanning electron microscopy (SEM) was used to examine the effect of surface modifications on repair surfaces and to evaluate the topography of fracture surfaces. Tukey-Kramer multiple-comparison test was used to detect significant differences between groups (p ≤ 0.05).

Results: SBS (MPa) of specimens treated with alumina blasting and application of intermediate agents were significantly higher than the control group (p < 0.05), while no significant differences were found between AB and control group (p > 0.05). Nano-ZrO₂ addition significantly increased SBS except for AB, and 5%, 7.5% MA (p > 0.05). SEM evaluation showed that alumina blasting created rougher and more porous surfaces, while SCA and MA reduced the irregularities and fissures.

Conclusion: Application of bonding agents to repair surfaces after alumina blasting improved the repair bond strength and proved to be a possible new adhesive method for denture repair. Moreover, nano-ZrO₂ addition in combination with surface treatment improved the repair bond strength.