Effect of Mechanical Design, Repair Material, and Surface Treatment on Impact Strength of Repaired Milled Computer-Aided Design and Computer-Aided Manufacturing Polymethyl Methacrylate: An In-Vitro Investigation

Background and Objectives: Impact strength evaluation aids in predicting the long-term behavior of polymethyl methacrylate under dynamic and real-life loading conditions. This study evaluates the impact strength of repaired digital polymethyl methacrylate using mechanical and chemical repair methods. Methods: Conducted at the Khanzad Center in Erbil, Iraq, between June 2023 and January 2024, this in-vitro study comprised nine groups. The control group received no treatment. Experimental groups were categorized according to bevel type, repair material, and surface treatments. Isometric bevel groups included: cold monomer treatment (Group A), Ivotion kit and monomer treatment (Group B), cold cure monomer with sandblasting (Group C), and Ivotion kit with monomer and sandblasting (Group D). Inverted bevel groups included: cold monomer treatment (Group E), Ivotion kit and monomer treatment (Group F), cold cure monomer with sandblasting (Group G), and Ivotion kit with monomer and sandblasting (Group H). Results: The inverted bevel design exhibited a higher mean impact strength (13.61 KJ/m²) than the isometric bevel design (11.16 KJ/m²), although this difference was not statistically significant (p = 0.089). Cold cure acrylic demonstrated significantly greater impact strength than the Ivotion bond kit (p < 0.001), regardless of bevel design. Regression analysis revealed a negative association between isometric bevel design and impact strength (B = -2.448, p = 0.004), while cold cure acrylic had a strong positive influence (Beta = 0.601). Conclusion: For the mechanical design, the inverse bevel repair design yielded a higher, though not significant, impact strength over the facing bevel design. Cold cure repair material showed significantly higher impact strength than the Ivotion kit material.