Fracture Resistance of Esthetic Prefabricated and Custom-Made Crowns for Primary Molars After Artificial Aging

Purpose: The purpose of this in vitro study was to compare the fracture resistance and survival of various esthetic crowns for primary molars after artificial aging via chewing simulation. Methods: A typodont tooth (mandibular primary second molar) was prepared to receive five different types of crowns as follows (n equals 10): prefabricated fiberglass (PF); CAD/CAM zirconia (CZ); CAD/CAM resin-ceramic (CR); composite- strip (CS); and prefabricated zirconia (PZ) as control. All specimens were subjected to 750,000 cycles of thermomechanical loading to artificially simulate three years of clinical service. None of the crowns from the CS group survived artificial aging. Surviving crowns were evaluated via micro-CT considering microcrack formation, and a load-to-fracture test was applied. Data were analyzed using one-way analysis of variance followed by the Duncan test. Results: Group PZ (557.4±170.1 N) and CR (669.6±255.2) were found to have comparable results (P >0.05), which were lower than the other groups (P<0.05). Group CZ resulted in the highest mean load-to-fracture value (1126.2±180.6; P <0.05). At the end of three years of artificial aging, microcracks were observed for only CS and PF groups. Conclusions: These in vitro data suggest that all tested crowns, except CS crowns, survived three years of artificial aging; however, CAD/CAM zirconia crowns may provide longer service, as they showed the highest fracture resistance with no microcrack formation.