Fracture Resistance of Maxillary Premolars Restored by Various Direct Restorative Materials and Techniques

Background and Objective: During the reconstruction of the lost tooth structure in deep mesio-occluso-distal (MOD) cavities, a combination of amalgam-composite restorations is suggested to simultaneously benefit from the composite resin and amalgam and to minimize their shortcomings. The aim of this study was to evaluate the fracture resistance and fracture mode of premolar teeth with MOD cavities restored by two combined amalgam-composite methods and compare it with intact teeth, amalgam and composite restorations. Methods: In this experimental in-vitro study, 60 intact maxillary premolars, which were extracted for orthodontic treatments, were randomly divided into 5 groups (n=12): Group I (control) included intact teeth and in the other groups, MOD cavities were prepared. Group II: amalgam restoration, Group III: composite restoration (Opalis, incremental filling), Group IV: 2 mm of gingival boxes were restored with amalgam and the rest of the cavities were filled with composite, Group V: 3 mm of gingival boxes were restored with amalgam and the rest of cavities were filled with composite. The samples were stored in distilled water for 24 hours at 37 ºC and underwent thermocycling (500 cycles). Specimens were subjected to a compressive load until fracture, and the fracture resistance was recorded in Newton. The fracture mode of samples was also recorded. Findings: The highest fracture resistance was seen in control group (817±120.3 N) and the lowest was in amalgam group (593±236.9 N), which was significantly lower than the control group (p=0.048). The difference in the fracture mode between the control group and the other groups was significant (p=0.006). Conclusion: Combined amalgam-composite restorations in MOD cavities can restore tooth strength to a level comparable to intact teeth and similar to conventional composite. The fracture mode was completely favorable only in the control group.