The Effect of the Thickness on Fracture Strength for Monolithic Zirconia Crowns

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Madalina-Elena Iorgulescu
Allyn C. Luke
David Ehrenberg
Saul Weiner


Purpose: This in-vitro study evaluated the effect of different thicknesses on load to failure of monolithic zirconia crowns (MZC), produced by computer-aided design/computer-aided manufacturing (CAD/CAM) after the combined effects of thermocycling and compressive load-cycling.

Materials and Methods: An Ivorine molar (#19) was prepared to receive an all- ceramic crown and replicated 60 times using highly filled epoxy resin (Viade Products Inc., Camarillo, California, USA). Sixty MZC crowns- of two different companies BruxZir and Diazir with 3 different thicknesses of 0.5 mm, 1 mm, 1.5 mm, were tested. All crowns were cemented to their dies using resin cement (Rely-X Unicem Clicker) and subjected to the following accelerated artificial aging program: water storage at 37ºC for 5 weeks, thermocycling (5-55ºC) for 8,000 cycles and load-cycling for 250,000 cycles (20 to 270 N). All samples were subsequently loaded in the central fossa area to fracture at a crosshead speed of 1 mm/min with a tungsten carbide ball of 3 mm in an MTS universal testing machine. Data was analysis by the Kruskal-Wallis test, followed by a Mann–Whitney test with Bonferroni correction, p < 0.05.

Results: Crown survival rates after artificial aging was 100%. Regarding the fracture loads there was a statistically significant difference among the three thicknesses of MZC, with a mean fracture loads in Newton (N) of: 0.5 mm- 1119.3 N (373.4 N), 1 mm- 1820.3 N (266.1 N), 1.5 mm- 2071.2 N (136.8 N). However, there were no significant statistical difference between the brands.

Conclusions: The thickness of MZC is a significant factor for the fracture strength of the restoration. Long term clinical studies are necessary before recommending all ceramic MZC for daily practice, especially the 0.5 mm thickness.

Zirconia, dental crown, implant-supported restoration, ceramic restoration, fracture strength.

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How to Cite
Iorgulescu, M.-E., C. Luke, A., Ehrenberg, D., & Weiner, S. (2020). The Effect of the Thickness on Fracture Strength for Monolithic Zirconia Crowns. International Journal of Research and Reports in Dentistry, 2(2), 1-8. Retrieved from
Original Research Article


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