Effect of Retainer Design on the Induced Strain and the Fracture Resistance of Lithium Disilicate Anterior Cantilever Bridges

Abstract

The purpose of this in vitro study is to evaluate the effect of retainer design (Full coverage retainers &Partial coverage retainer) under two direction of loading: (Vertical loading & Lateral loading on the induced strain and fracture resistance of lithium disilicate (IPS e.max press) anterior cantilever bridge. A total of 30 all-ceramic heat pressed e.max cantilever bridges were constructed and divided according to bridge and retainer design into three main groups (10 bridges each).: Cantilever bridge with Full coverage retainer, Cantilever bridge with partial coverage Three-Quarter retainer., Fixed- fixed bridge with full coverage retainer. Each group was further divided according to the direction of loading into two subgroups (5 bridges each): Vertical loading (Parallel to tooth long axis), Lateral loading (45 degree from tooth long axis). Fracture resistance and strain of samples were then tested. The results showed that there was a statistically significant interaction between direction of load and design of the restoration regarding the fracture results. Regarding the strain, there was a statistically significant interaction between direction of load and design of the restoration regarding the fracture results. There was a strong positive correlation between Fracture Load