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

Abstract

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. 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). 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. 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.