Comparative Evaluation of Microhardness between Monolithic and Multilayered Zirconia: An in-vitro Study

This study aimed to evaluate and compare the microhardness of monolithic zirconia and multilayered zirconia to investigate the influence of material composition and structural design on their mechanical properties. ‏Cylindrical specimens were designed using AutoCAD software and fabricated from monolithic zirconia (Group A) and multilayered zirconia (Group B blocks via CAD/CAM milling systems. The specimens were sectioned into discs with a diameter of 10 mm and a thickness of 1.5 mm. Microhardness testing was performed on these discs using a standardized protocol. Statistical analysis was conducted using a student’s t-test (P < 0.05) with a sample size of 10 specimens per group to ensure 80% power and 95% confidence. ‏Results revealed significant differences in microhardness between monolithic and multilayered zirconia. Monolithic zirconia exhibited superior hardness, attributable to its single-layered structure, which enhances its mechanical strength and wear resistance. In contrast, multilayered zirconia, while exhibiting lower microhardness, demonstrated esthetic advantages due to its gradient layering and maintained sufficient durability for clinical use. ‏The findings underscore the impact of zirconia composition and structural design on mechanical properties, providing clinicians with valuable insights for material selection. While monolithic zirconia is ideal for high-load posterior restorations, multilayered zirconia offers an esthetic solution with adequate mechanical performance, making it suitable for anterior applications.