Retentive Force Assessment and Wear Exploration of CAD-CAM Fabricated PEEK, Zirconia, and PMMA Mini Ball Attachments...

Background/Objectives: The longevity of tooth-supported overdentures depends on the retentive stability of attachment systems, yet limited evidence exists on the performance of non-metallic CAD-CAM fabricated mini ball attachments. This study aimed to evaluate the retentive force changes and surface wear of CAD-CAM fabricated mini ball attachments made of zirconia, polyetheretherketone (PEEK), and polymethyl methacrylate (PMMA) for tooth-supported overdentures. Methods: Twenty-one mandibular canine replicas received CAD-CAM copings with mini ball attachments (n = 7 per material). Retentive force was measured at baseline and after 90, 270, 540, 1080 and 2160 insertion-removal cycles (simulating 2 years of clinical use). Surface wear was examined under scanning electron microscopy (one specimen per group, preliminary). Data were analyzed using one-way ANOVA, paired t-tests with Bonferroni correction, and mixed repeated-measures ANOVA (Greenhouse-Geisser correction). Effect sizes (partial η², Cohen's d) were calculated. Based on a priori power analysis 7 specimens per group were decided. Results: All materials showed a significant decline in retention over cycles (p < 0.001, partial η² = 0.90). No significant differences were found among the three materials at any time point (p > 0.05). The material × time interaction was not significant (p = 0.064). Within each material, baseline-to-final reductions were significant (p ≤ 0.009, Cohen's d > 3.0). Exploratory SEM suggested minimal wear for zirconia, moderate for PEEK, and pronounced surface deterioration for PMMA. Conclusions: Within the limitations of this study, all three CAD-CAM mini ball attachments provided decreasing but measurable retention over simulated use. Zirconia showed numerically the highest final retention, but no statistically significant differences were detected among materials. Clinically, zirconia attachments demonstrated numerically superior final retention with minimal wear, suggesting potential advantages for long-term use; however, the lack of statistically significant differences among materials and the preliminary nature of the wear analysis warrant caution, emphasizing the need for future clinical validation before definitive material recommendations can be made.