Effect of Crown Thickness and Abutment Taper on the Fracture Resistance of Monolithic Zirconia Crowns: An In Vitro Study

Introduction: Monolithic zirconia permits conservative tooth preparation while providing high mechanical strength.However, the effects of reduced crown thickness and abutment taper on fracture resistance require further evaluation.This study aimed to evaluate the effects of monolithic zirconia crown thickness and abutment taper on fracture resistance and determine whether these factors influence fracture load.Materials and methods: This in vitro study evaluated 48 standardized typodont dies restored using computer-aided design/computer-aided manufacturing (CAD/CAM)-fabricated monolithic zirconia crowns.The crowns were divided according to thickness into 0.5 mm, 1.0 mm, and 1.5 mm groups, with each thickness further subdivided into 5° and 10° abutment taper groups (n=8 per subgroup).The specimens were cemented using dual-cure resin cement, thermocycled for 5,000 cycles between 5°C and 55°C, and subjected to compressive loading with a 4 mm spherical indenter at 1 mm/min until fracture.Fracture load was analyzed using two-way analysis of variance, independent-samples t-tests, and Tukey's honestly significant difference post hoc test.Results: The mean fracture load increased progressively with crown thickness.For the 5° taper, the mean fracture loads were 1,498 N, 2,429 N, and 3,612 N for 0.5 mm, 1.0 mm, and 1.5 mm crowns, respectively, and the corresponding values for the 10° taper were 1,018 N, 2,124 N, and 3,212 N. Crown thickness significantly affected fracture load (p<0.001;partial η²=0.899), as did taper (p<0.001;partial η²=0.310).The thickness × taper interaction was not statistically significant (p=0.735).Tukey's comparisons showed significant differences among all thickness levels (p<0.001).Conclusion: Greater zirconia thickness and lower abutment taper were associated with higher fracture resistance under the tested conditions.These findings highlight the importance of both crown thickness and preparation geometry in optimizing the mechanical performance of monolithic zirconia crowns.Further clinical studies using fatigue loading and more representative oral conditions are warranted.