Fracture resistance of monolithic zirconia crowns: The importance of the compressive strength of the dental cements used.

Abstract

Background: Monolithic zirconia crowns have not been used for a very long period in dentistry even though zirconia with veneering porcelain, as crown and bridge material has been used for several years with great clinical success. Several different luting materials have been purposed for zirconia but concerning monolithic zirconia the knowledge of the influence of the cement seem to be limited. The aim of the study was to investigate three different cements (one phosphate, one self adhesive and one dual cured resin based cement) and their influence on fracture strength of monolithic zirconia crowns in vitro with the null hypothesis tested that the compression strength of the cement would have no statistical influence on the fracture strength of the monolithic zirconia crowns tested. Materials and methods: Eighteen CAD-CAM produced monolithic zirconia crowns (Th=0.5 mm) divided into 3 groups (n=6) and cemented with 3 different cements were tested. In advance the Poissons ratio, modulus and flexural strength of the composite abutment used, fit of the crowns and their quality was evaluated. Two tests were then conducted for the cement study: Compressive strength of the cements used were tested and recorded as well as load to failure test. The 3 groups of crowns cemented with the three different cements were tested until fracture after water storage for 24 hours at 37°C±1. The tests were done with guidance of ISO 9917:1 and comparative test procedures for load to failure test. Light microscope and SEM analysis were conducted and differences between the groups tested were statistically evaluated. Results and conclusion: The composite abutment showed similar Poissons ratio and modulus values as wet dentin. Even though the phosphate cement showed significantly less compressive strength, no significant difference in load to failure for the crowns tested were found. The compressive strength of the cement used seemed to be of no importance for the fracture resistance of monolithic zirconia crowns.