Effect of Incorporating Zirconia–Hydroxyapatite Particles into Heat-Cured Polymethyl Methacrylate Resin on Surface Hardness, Roughness, and Flexural Strength: An In Vitro Study

Introduction: We aimed to evaluate the surface hardness, roughness, and flexural strength of heat-cured polymethyl methacrylate (PMMA) resin after incorporating zirconium–hydroxyapatite (ZrO 2 –HA) particles at concentrations of 1, 2.5, and 5 wt.%. Methods: In total, 120 samples have been synthesized and divided into four groups based on ZrO 2 –HA wt.% incorporation. All samples underwent surface roughness, surface hardness, and flexural strength tests. Results: Flexural strength tests revealed significant differences among study groups ( P < 0.001). The surface roughness test did not reveal significant differences among study groups ( P = 0.336), whereas surface hardness tests showed significant differences among study groups ( P < 0.001). Conclusion: Incorporation of ZrO 2 –HA particles at concentrations of 2.5 wt.% can improve the surface hardness of PMMA without affecting surface roughness.