Comparing Marginal Fit and Marginal Gap between Sholder Bevel and 135° Finish Line Designs in Posterior Metal Ceramic Restoration Crowns

Background and purpose: One of the major challenges for dentists is providing the patients with a crown of appropriate marginal fit and marginal gap. Preparation of a 135° finish line has some advantages such as technical ease and appropriate finish line record. Nevertheless, few studies investigated this type of finish line. The current study aimed at comparing marginal fit and marginal gap in 135° finish line and shoulder bevel finish line. Materials and methods: In this quasi-experiment study, 135° finish line and shoulder bevel finish line were performed in two first mandibular molars with healthy coronal tissue and similar size. Impression was taken from each tooth and 31 crowns were made on each die. Samples plastered with fit checker were pressed under 40 N for three minutes in universal testing machine. They were measured and recorded under a loop with 40x power at three points on each side. To analyze the data, Wilcoxon and Kolmogorov-Smirnov tests were applied in SPSS V24. Results: Mean values for the marginal fit in shoulder bevel and 135° finish line were 55.0907 µ and 55.2587 µ, respectively. The mean values for marginal gap were 19.7245 µ and 0.9745, respectively (P=0.000). Conclusion: According to current study, a 135° finish line may have better clinical efficacy than a shoulder bevel.