Method: seventy two extracted human mandibular first molars satisfying certain predetermined criteria were subjected to five different restoration methods (12 molars per method). After endodontic treatment, in each specimen restoration was carried out by one of the following methods: group 1 = control (intact molars); group 2 = using composite restoration; group3= amalgam restoration groups 4, 5 and 6 = restoration using inlay, onlay and zirconium crowns, respectively. A fracture test was conducted to determine the fracture resistance and fracture mode of each specimen using static load with Instron machine. Favorable and unfavorable fractures were recorded.
Result: Fracture resistance was greatest for teeth restored using composite restorations and the teeth restored using zirconium was also high with mean values of 1480.33 N and 1388.75 N respectively, with no significant difference. Fracture resistance for teeth restored using inlay was significantly the lowest (718.33 N) compared to the rest of the groups, it showed that the composite restorations group had the highest unfavorable fracture (100%) compared to the zirconium crown group with the highest favorable fracture (66.7%), and in other groups most of the fractures were unfavorable.
Conclusion: Endodontically treated mandibular first molars with conservative cavity restored with direct composite restoration or zirconium crown had comparable fracture resistance in this laboratory study compared to other restorations. Fracture with composite restoration group was always nonrestorable. Further clinical studies are required to confirm this conclusion.