Effect of Framework Material and Thermal Aging on Shear Bond Strength of Three Different Gingiva-Colored Composite Resins

The purpose of this study was to evaluate the effect of different framework materials and thermal aging on the shear bond strength (SBS) of gingiva-colored composites used in fixed dental restorations. A total of 270 samples (10 × 10 × 2 mm³) were prepared using titanium, zirconia, and modified polyetheretherketone (modified PEEK). Three gingiva-colored composites (Gradia Gum, Anaxgum, Nexco) were applied after surface polishing and sandblasting. All specimens were stored in water at 37 °C for 24 h, then half of each group was subjected to thermal aging consisting of 10,000 cycles at temperatures between 5 and 55 °C. SBS testing was performed using a universal testing machine with a crosshead speed of 1 mm/min. Bonding failures were analyzed under a stereomicroscope, and one sample from each group was examined using a scanning electron microscope. SBS data were analyzed using three-way ANOVA with composite type, framework material, and thermal aging as factors, followed by pairwise comparisons (SPSS 23.0; p < 0.05). The highest SBS was recorded for the zirconia framework combined with Gradia Gum, specifically in the group without thermal aging (p < 0.05), while the lowest was observed for zirconia combined with Nexco after thermal aging (p < 0.05). Adhesive failures were predominant in the modified PEEK groups, whereas mixed failures occurred more frequently in titanium and zirconia groups. Both composite type and framework material significantly influenced SBS values, with thermal aging having a detrimental effect across all groups. This study demonstrates that both framework material and composite type affect bond strength, with specimens not subjected to thermal aging maintaining better adhesion. Thermal cycling reduced SBS in all groups, although the extent varied by material combination.