Hardness and Density of Conventional and Monolithic Zirconia after Sintering

Abstract

Background: Zirconia (zirconium dioxide, ZrO2) has optimum properties for dental use. Its main advantages include biocompatibility, biomechanical stability, and high fracture resistance. This in vitro study aimed to determine and compare the hardness and density of conventional and monolithic zirconium after the laboratory sintering process. Methods and Results: This experimental-comparative study was carried out on processed samples of zirconia blocks, determining their mechanical properties and comparing them between different zirconia materials. Conventional zirconia blocks (from Dentsply Sirona Cercon HT and Orodent Zirconia HT) and monolithic zirconium blocks (from Dentsply Sirona Cercon ML and Orodent Zirconia Thor) were processed to produce 80 molar crowns. Samples were divided into two groups: Sirona[S]–Orodent[O]/Conventional [C] group (n=40) and Sirona[S]–Orodent[O]/Monolithic [M] group (n=40). Sirona samples were divided into Sirona-Conventional (SC) subgroup (n=20) and Sirona-Monolithic (SM) subgroup (n=20); Orodent samples were divided into Orodent-Conventional (OC) subgroup (n=20) and Orodent-Monolithic (OM) subgroup (n=20). Samples were formed with an occlusal thickness of 2mm and were sintered at 1450 °C for 2 hours. Hardness expressed in Vickers Hardness Number (VHN) was performed using a microhardness tester (Model HV-1000DT), and density determination (g/cm3) was performed with a pycnometer. The results showed no significant differences (P=0.137) between the Sirona manufacturer's SC and SM subgroups. The subgroups of the Orodent manufacturer showed statistically significant differences: the OM subgroup had a higher hardness value than the OS subgroup (1654.95±140.731 VHN versus 1526.45±149.011 VHN, P=0.008). Among the four studied subgroups, the highest hardness was in the OM subgroup (1654.95±140.731 VHN) compared to the SC subgroup (1595.55±147.790 VHN), OC subgroup (1526.45±149.011 VHN), and SM subgroup (1525.95±142.081 VHN) (P=0.016). Density in the subgroups SC, OC, SM, and OM was 6.246 g/cm3, 6.081g/cm3, 6.217 g/cm3, and 6.187 g/cm3, respectively, without statistically significant differences (P>0.05). Conclusion: The findings highlight the suitability of both zirconia materials from Dentsply Sirona and Orodent manufacturers for dental restorations, with Orodent monolithic zirconia offering potential advantages in terms of hardness.

Keywords

• conventional zirconia
• density
• hardness
• monolithic zirconia
• sintering