Aim: compare fracture strength of composite restorations (methacrylate resin-based, methacrylate free) restoring abutments having occlusal rest seat in them and applying vertical stresses through the rest.
Materials and Methods: 28 extracted first maxillary premolars were used, class II cavities were prepared. According to composite restoration, specimens randomly into two equal groups; first group methacrylate resin-based composite Tetric N-ceram® while in second group Ormocer-based composite (methacrylate-free) Admira fusion®. Saucer rest seats were prepared, then samples were stored in distilled water for 2weeks and exposed to thermo-cycling. Metallic tool milled with dimensions of RPD rest was used in universal testing machine applying vertical load where fracture resistance test used. In-addition, site of fracture and fracture mode were inspected under optical light microscope. All records were tabulated and analyzed.
Results: Results showed, Tetric N-ceram samples had higher strength values (1189.00±27 N) than those of Admira fusion (1012.40±25 N), yet difference wasn't statistically significant (p=0.06). There was equal distribution of fracture site in both groups, commonly mixed type (100%). While fracture mode, Tetric N-ceram group, 28.5% showed non-catastrophic mode and 57.1% in Admira fusion group. Besides, Tetric N-ceram showed 71.43% catastrophic mode while 42.86% in Admira fusion group.
Conclusion: There was no significant difference in fracture resistances of resin composite restorative materials compared to resin free. Tetric N-Ceram and Admira can be considered suitable restorative material used under rests of RPDs and safely support them.