A Comparative Evaluation of the Effectiveness of Added Auxiliary Features, Occlusal Surface Modifications, and Reduction of Total Occlusal Convergence on the Resistance of Full Veneer Metal Crowns on a Molar Tooth with Inadequate Resistance Form: An in vitro Study.

Abstract

Introduction:Single crowns or fixed partial dentures retainers usually get dislodged due to inadequate resistance form. Hence, it is prudent to evaluate features of a tooth preparation, which can prevent these failures.Aim:To evaluate the effect of auxiliary features, occlusal surface modifications, and total occlusal convergence (TOC) on the resistance of a full veneer crown.Materials and Methods:An ivorine mandibular molar tooth was prepared with features of inadequate resistance form, i.e., 2.5 mm axial wall height and TOC of 20°. Seven auxiliary preparation features were subsequently added one by one to it. They were mesiodistal grooves, buccolingual and mesiodistal grooves, buccolingual grooves, mesiodistal boxes, occlusal inclined planes, 8° reduced TOC in the cervical aspect, and mesiodistal grooves added to 8° reduced TOC in the cervical aspect. Ten dies with their respective crowns were prepared for each group. Resistance testing of all the samples was performed on the INSTRON testing machine.Results:Modification of the overtapered die preparation by reducing the TOC to 8° in the cervical 1.5 mm of the axial wall and then subsequently adding mesiodistal grooves to the reduced TOC cervically offered the greatest resistance to dislodgment statistically.Conclusion:For an overtapered preparation, reducing the TOC to 8° in the cervical aspect and subsequently adding proximal grooves can provide maximum resistance form.