Effect of adhesives and mechanical surface treatments on the hard relining of CAD-CAM denture bases

Purpose: The aim of this study was to evaluate the impact of mechanical roughening, adhesive applications, and aging on the bonding between CAD-CAM denture base materials with distinct chemical contents and hard relining material. Materials and Methods: A total of 300 denture base specimens were produced by additive, subtractive, and conventional heat-polymerization techniques (N = 100). The specimens have been classified into five subgroups based on the particular surface treatments administered (n = 20): (1) Hard relining material's adhesive application (control); (2) Tungsten carbide bur application for 1 min, and hard reline material's adhesive application; (3) Airborne-particle abrasion (APA) with 110 μm AlO, and hard reline material's adhesive application; (4) Scotchbond Universal application; and (5) Visio.link application. Representative specimens from each subgroup were examined under a Scanning Electron Microscope (SEM). Subsequently, self-cure hard relining material was condensed in the center of the specimens. Half of the specimens were thermally aged with 5000 cycles at 5°C–55°C. The shear bond strength (SBS) test was performed, and failure loads were recorded. The data was evaluated by Robust ANOVA and Bonferroni test (p < 0.05). Results: No statistically significant difference was obtained between the production techniques (p = 0.051). The lowest SBS was observed in the control group among surface treatments, while mechanical surface treatments and universal adhesive showed the highest SBS for both aged and non-aged groups. Aging caused a significant decrease for all test groups (p = 0.001). Conclusions: Mechanical surface treatments and universal adhesive applications are more effective for maintaining adhesion across all production techniques.