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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.

Background: Fewer studies were conducted on resistance form. This study evaluated the effect of different auxiliary features on inadequate resistance form. Aim: The aim of the study is to evaluate the resistance at 22° taper with reduced occluso-cervical height with different auxiliary features. Methodology: An ivorine tooth was prepared with computer-aided design-computer-aided manufacturing with total occlusal convergence (TOC) of 22°, shoulder finish line 0.9 mm wide, reduced occluso-cervical height, i.e., 2.5 mm, and reduced diameter. The crown preparation was subsequently modified to include interproximal grooves, interproximal boxes, and reduced TOC in the axial wall from 22° to 8° in the cervical 1.5 mm of the axial wall. A total of four groups with ten standardized metal dies were prepared for each design with the computer-aided milling machine. Standardized complete metal crowns using silicon mold were fabricated and cemented on metal dies with glass ionomer cement. The resistance of each specimen was evaluated when force was applied at a 45° angulation to the long axis of the die in a lingual to buccal direction by a universal testing machine. The values were then analyzed using one-way analysis of variance test and post hoc Bonferroni test. Results: The comparison of the mean resistance test values was done among all the groups, and there was a significant (P ≤ 0.001) difference found among the groups. Conclusion: The most effective method of enhancing resistance form preparation is to decrease the TOC of the cervical portion of the prepared axial walls. Two interproximal boxes significantly increased the resistance form. However, two interproximal grooves did not significantly increase the resistance form.

Aims: Resistance form of full metal-ceramic crown is an important feature that determines longevity of these restorations. This study evaluated the resistance form of full metal-ceramic prepared with four different design features. Materials and Methods: An acrylic tooth was prepared with 20° total occlusal convergence (TOC) angle, 2.5 mm of occlusocervical dimension and a shoulder finishing line. This design lacked resistance form. The crown preparation was subsequently modified by preparing Mesial Occlusal Distal isthmus, placing occlusal inclined plane, and reducing TOC. Four metal dies from these designs were constructed by lathe machine and then 10 metal copings were fabricated for each preparation. Metal coping were cemented on metal dies with temp-bond cement. Force was applied at 45° from lingual to buccal direction with universal testing machine. Statistical analysis used: The data were evaluated by Kruskal-Wallis and non-parametric Mann-Whitney test. Results: All features increased resistance form when compare to control group. However, reduce TOC group showed greatest value of resistance. Conclusion: Within the limitation of this study, reducing the tapering of occlusocervival dimension is the most effective way in increasing resistance form, although, other features were also effective.