Evaluation of the fracture strength of different CAD/CAM manufactured implant supported crowns and force transmission to the implant

Implant supported restorations have been widely used in replacement of missing teeth. Since the improvements in CAD/CAM technology make an increase in the use of all ceramics and the complications resulted by the biomechanical differences made the occlusal materials for implant-supported restorations have been a topic of research interest, the purpose of this study was to evaluate the fracture strength of different CAD/CAM manufactured implant supported crowns and comparison of stress distribution in bone and implant components with FEA. Materials are divided into six groups; Group L-M: Lithium disilicate ceramic (Monolithic), Group L-T: Lithium disilicate ceramic (Conventional Layering), Group LZ-M: zirconia reinforced lithium silicate ceramic (Monolithic), Group LZ-T: zirconia reinforced lithium silicate ceramic (Conventional Layering), Group CF: zirconia veneered with feldspathic ceramic (CAD-on), Group CL: zirconia veneered with lithium disilicate ceramic (CAD-on). The restorations were subjected to fracture load testing at a 0.5 mm/min crosshead speed to measure the fracture strength. The fracture strength values of each group were statistically analyzed (ANOVA, Post Hoc Tukey HSD, α=0.05). There was a statistical difference between group L-M, group CL and the other groups (p>0.05), but there was not a significant difference between the group L-T, LZ-M, LZ-T and CF (p<0.05). Group CL had the highest fracture strength (4649,22 ± 733,42 N), followed by L-M (2891,88 ± 410,12 N), LZ-T (2202,55 ± 503,14 N), CF (2085,91 ± 555,61 N), L-T (2077,37 ± 356,59 N), LZ-M (1750,28 ± 314,96 N). After fracture load test, fractographic analysis was used and the abutment-implant complexes were checked for the presence of any complications. The FEA results showed that the restorative materials did not affect the stress distribution on implant components, while the monolithic restorations reduced the stress on implant and bone.