A Comparison of the Edge Testing of Indirect Composite Layered Zirconia Crowns and Monolithic Zirconia Crowns Without Aging: An In Vitro Study

Introduction The main reason veneered zirconia restorations fail is due to porcelain veneer chipping. This chipping usually starts from wear marks on the chewing surface. As a result, small cracks under the contact area can grow into larger ones across the veneer layer. The veneer ceramic layer is more vulnerable to fractures because it has lower toughness and slightly lower stiffness compared to the base framework material. Thus, even when there's significant chipping, the main framework material usually stays protected with a thin layer of veneer ceramic on top. The aim of this in vitro study is to compare the edge strength of Monolithic Zirconia Crowns with that of Indirect Composite Layered Zirconia Crowns without aging. Materials and methods This research involved creating 12 hand-layered all-ceramic crowns and 12 indirect composite layered zirconia crowns. The sample size was determined using a G*Power calculation (Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany). The zirconia frameworks (Upcera HT White; UPCERA Dental America Inc., Cerritos, CA, US) were milled and sintered following the manufacturer's instructions. For the all-ceramic group, veneering porcelain (e.max Ceram; Ivoclar Vivadent, Schaan, Liechtenstein) was hand-applied. In contrast, the indirect composite group utilized Ceramage (Shofu, Kyoto, Japan). An Instron 4501 universal testing machine (Instron Corp., Canton, MA, USA) was employed for the edge chipping tests, and a Vickers indenter (Shanghai Toyo Diamond Tools Co., LTD, Shanghai, China) was used to apply the load. The mean value for edge chipping was analyzed using an unpaired t-test with IBM SPSS Statistics for Windows, Version 26 (Released 2019; IBM Corp., Armonk, NY, USA). The normality of the data was confirmed, and statistical significance was set at 0.05. Results Monolithic Zirconia Crowns (Group 1) require significantly more force (mean: 405 N) to induce an edge chip compared to Indirect Composite Layered Zirconia Crowns (Group 2) (mean: 300 N). The 95% confidence interval (83.43261 N to 109.90072 N) confirms the statistical significance of this difference. Conclusion In conclusion, when evaluating restorative materials based on both esthetic and functional criteria, monolithic zirconia stands out due to its combination of strength, esthetic potential, biocompatibility, and versatility.