THE EFFECT OF TOOTH PREPARATION TAPER ON THE MARGINAL FIT AND FRACTURE RESISTANCE OF CAD/CAM ZIRCONIA COPINGS

Introduction: Clinical fracture resistance and marginal fit are regarded as major outcomes when considering the performance of all -ceramiccrown. Modifying axial wall tapering may influence on marginal fit and fracture resistance.Objectives: To investigate the effect of tooth preparation taper on marginal adaption and fracture resistance of CAD/CAM zirconia ceramiccopings.Materials and methods: A machined standard stainless steel dies representing lower first molar were made and fixed to a metal base to stimulatesingle prepared crowns with three different axial wall convergence angles (6°, 12°, 22°). Master dies were duplicated using silicon mold after whichfifteen crowns were reproduced for each group using epoxy resin material. All cores were fabricated using cercon zirconia and adhesively luted onepoxy resin dies. Measurement of marginal fit was performed with cone beam computed tomography. Specimens were subjected to fractureresistance test. The failure modes and points of fracture will be recorded. Data were statistically analysed using ANOVA test.Results: The results showed significant difference between three tested groups in marginal adaption, where 22 degree had significantly the best fitalso there was significant difference between three tested groups in fracture resistance, where 22 degree have showed highest fracture load.Conclusion: Within the limitations of this in vitro study, increasing the axial convergence angle of CAD/CAM zirconia core improved theirmarginal fit and increased their fracture strength.