In Vitro Comparison of Porcelain Fused to Metal Crown Retention after Endodontic Access and Subsequent Restoration: Composite, Amalgam, Amalgam with Composite Veneer, and Fiber Post with Composite

Introduction: The aim of this study was to evaluate the effect of different access opening restorative materials on crown retention. Methods: Thirty-eight extracted molars were mounted in resin and prepared for porcelain fused to metal (PFM) crowns. The crowns were fabricated and cemented with zinc phosphate, and the force to displace it was measured with a tensile-testing machine before and after endodontic access preparations. The endodontic access area, crown preparation axial wall, and preparation surface area were measured for comparison. The crowns were then recemented, and access openings were restored with either amalgam or composite before displacement force was remeasured. The restorative material was removed from each access opening; access area was measured and restored again (amalgam with composite or fiber post with composite) for displacement force to be remeasured. Paired t test was used to compare the means of displacement between groups. One-way analysis of variance was used to compare the mean outcome measure within the groups. Results: Statistical analyses showed retention after unfilled access was significantly lower than intact crowns. Amalgam, composite, amalgam + composite, and fiber post + composite increased retention beyond the original value. There was no statistical difference among the different restorative protocols. Qualitative results indicate that the restorative material remains in the crown after displacement regardless of the material used to restore the access. Conclusions: The results from this study suggest that an endodontic access cavity decreases retention of a PFM crown. However, subsequent restoration with amalgam, composite, amalgam + composite, or post + composite may increase the original retention of the crown.