مقارنة مقاومة انكسار التيجان الخزفية المعدنية ذات السوار المعدني والحافات الخزفية مخبرياً

Background & Objective: The idea of use ceramic margins for metal-ceramic crowns was founded to overcome problem of grayness for gingival margins that caused by metal collar in metal-ceramic crowns , but at the same time there are a lot of cautions on decrease mechanical resistance for these restorations. This study aims to study fracture resistance of metal-ceramic crowns with ceramic margins in 1 or 2 mm. long, and compare it with mechanical resistance of metal-ceramic crowns with metal collar. Material& methods: Upper acrylic central incisor was prepared for metal-ceramic crown , then casted with Ni-Cr alloy to get the master die . 45 metal substructures were fabricated and divided in 3 groups. metal substructures were cut back 1 mm all around margin area in group I and 2 mm in group II , nothing was doing for metal in group III .Building of ceramic crowns were completed , and direct lift technique was used for ceramic margins build-up .The crowns were tested by using a universal testing machine, compression load was applied until ceramic failure occurred . results were studied statistically using Anova one-way test and Bonferroni test (p>0.05). Results: Results defined that average load when failure occurred at 500.31 N in group I , 350.54 N in group II , and 559.82 N in group III. With statistically significant differences between group II and III . Conclusions : Metal-ceramic crowns with metal collar have the greatest resistance ,while this resistance decreased as well as cutting back from crowns′ metal substructure increased , with average load were applied on metal-ceramic crowns with ceramic margins were stayed between expected forces on front teeth during function. This thing allow to use these crowns in clinical use especially crowns in group I