To Determine and Compare the Average Amounts of Resistance of Four Features of Preparation on First Mandibular Molar Full Metal Crowns

Introduction: Full coverage of teeth chosen correctly, could be the best treatment, but because of different steps involved in crown fabrication, dentists must try to make crowns with noticeable duration. The purpose of this study was to evaluate the effect of auxillary preparation elements and occlusal surface modifications on the resistance form of a complete lower molar crown.Methods and materials: This study was of experimental-laboratory type. Ivorine tooth was prepared with 20 degree TOC (Total Occlusal Convergence), 3 mm occlusocervical dimension and shoulder finishing line (First group=control group). Ten standard metal dies were replicated from this model. Standard metal crowns were made for all samples. After the cementation of metal crowns to metal dies with resin cement, the resistance of each samples against lateral forces were determined by instron machine. Next groups consisted of interproximal boxes+ buccolingual grooves (2nd group), occlusal isthmus (3rd group) and reduced TOC at cervical area (4th group) prepared on control group. The other procedures were done the same as for the control group. Data from 4 groups were evaluated by ANOVA and Post Hoc tests.Results: Statistical analysis of the results showed the most significant differences were in the 4th group and then the second group (239.1 and 178.5 kgf respectively). While no statistical differences were found between groups "1&3" (93.8 and 94.7 kgf respectively).Conclusion: The best axial preparation to increase the resistance form was reduced TOC. Preparing boxes+grooves were of second impatance. However lack of axial preparation (group "A") or auxiliary features without favorable effects such as occlusal isthmus (group "C") on teeth with insufficient resistance form does not have any positive effect.Key words: Resistance, Axial preparation, Total occlusal convergence