Résumé
One of the problems of all ceramic restorations is their risk of fracture due to occlusal loads.The aim of the present study was to compare the effect of two marginal designs [shoulder and chamfer] on the fracture resistance of IPS-emax all ceramic restorations.One extracted maxillary first premolar received chamfer 50' marginal preparation [0.8 mm].Twenty impressions were made using poly vinyl siloxane. Then, chamfer was converted to shoulder 90'[1mm]. Afterimpression, epoxy resin dies were fabricated. Impressions of each epoxy resin die were made and poured with diestone. Twenty Press crowns and twenty ZirCAD crowns were made on stone dies and cemented on resin dies. Then,samples underwent a fracture test in a universal testing machine. Data were analyzed by one-way ANOVA.The mean fracture resistance was 1426N for the chamfer ZirCAD samples, 1361.3N for the shoulder ZirCADsamples, 1059.9N for the chamfer Press samples and 1295.8N for the shoulder Press samples. One-way ANOVA revealed no difference among groups. [p=0.095].After porcelain application, marginal design does not affect fracture resistance of single IPS-emaxposterior crowns. Fracture resistance was approximately the same in Press and ZirPress groups probably due to porcelain application, because in ZirCAD group fractures occurred in the porcelain prior to the core
Résumé
Demand for implant supported overdentures has increased due to the problems of conventional dentures. Despite the high success rate of implants, implant failure remains a major challenge. Implant overload can cause cortical bone loss and implant failure. Using finite element analysis, this study aimed to find the best design and type of attachments causing minimum stress in the alveolar bone. The geometrical model of the mandible was produced using computed tomography [CT] data and three ITI implants were placed in the midline and the location of the first premolar teeth. All conditions were simulated using finite element software. Three bar-ball, bar and ball attachments were considered to support the overdenture. Maximum von Mises stress was calculated in the supporting bone in different overdenture designs. The results showed that the greatest amount of stress in bone was around the upper thread and the neck of the implant. The ball and the bar-ball attachments applied the most and the least amount of stress to the bone around the implant, respectively. Maximum stress was applied to the ball attachment in the bar-ball design. The maximum amount of movement was in bar-ball attachment. The bar-design decreased the stability of overdenture, as well as the stress in the peri-implant bone. Ball design increased concentration of stress in bone around the implant and increased the stability of overdenture