Evaluation of Retention Force Between PEEK Posts with Different Surface Treatments and Resin Composites for Core Build-Up by a Pull-Out Test—Effect of Thermal Cycling

This study evaluated the retention force between milled polyetheretherketone (PEEK) posts with different surface treatments and resin composites for core build-up, and the effect of thermal cycling on the retention force. Four groups of PEEK posts were prepared: untreated group (NT), mechanically treated group with sandblasting (SB), chemically treated group with primer application (AD), and a group combining mechanical and chemical treatments (SB+AD). Pull-out tests were conducted on these groups. The specimens were divided into two subgroups: one stored in a humid environment at 37 °C for one week (TC0) and the other subjected to 10,000 cycles of thermal cycling between 5 °C and 55 °C (TC10,000). Data were analyzed using two-way ANOVA and Tukey’s test. Additionally, the effect of thermal cycling on each group was examined using Student’s t-test. Both surface treatment and thermal cycling factors had statistically significant effects on retention force (p < 0.05). The interaction between these factors was also statistically significant (p < 0.05). The results showed that the retention force of the treated groups was significantly improved compared to the untreated group, with the SB+AD group exhibiting the highest retention force, followed by the SB group and then the AD group. Thermal cycling did not affect the retention force in the NT, SB, and SB+AD groups. These findings suggest that the combination of mechanical and chemical surface treatments is the most effective method for improving the retention force between PEEK posts and resin composites for core build-up. Furthermore, appropriate surface treatment of PEEK posts may influence their long-term durability.