Fracture resistance and failure pattern of different cavity designs

Methods: 60 extracted third molars were divided into 6 groups (n=10): G1: sound teeth (control); G2: non-restored mesio-occlusal-distal (MOD) preparation being the vestibular cusp in enamel without dentin support (negative control); G3: MOD + glass ionomer (Vidrion R/SSWhite) to substitute the dentin support + resin-composite (Tetric-Ceram/Ivoclar-Vivadent); G4: similar to G3 but fully restored with resin-composite; G5: part of the enamel in the vestibular cusp was removed and fully restored with resin-composite; and G6: the enamel without dentin support in the vestibular cusp was completed removed and cavity fully restored with resin-composite. The adhesive system used for all groups was Scotchbond Multi-Purpose/3MESPE. Teeth areas were calculated and specimens submitted to compression test in a universal testing machine (DL2000, EMIC) at a constant speed of 0.5 mm/min. Specimens were loaded until fracture. Fracture patterns were classified according to five types based on reconstruction possibilities (direct, onlay, indirect crown, endodontic treatment+ posts + indirect crown and extraction). Data were submitted to ANOVA and Tukey's test or Kruskall-Wallis (5%).

Results: G6 was the only group that showed fracture resistance similar to the control G1 (19.5±3.4). No statistical difference was observed among G3 (11.0±4.7), G4 (10.5±3.1), G5 (13.3±3.9) and G6 (15.1±2.5). Lower fracture resistance values were observed in G2 (5.6±2.8). According to fracture pattern, in 71% of the cases it was possible to reconstruct the teeth either with direct or onlays restorations. Teeth allocated in G5 and G6 showed higher rate (35%) of catastrophic failure than G3 and G4 (0%).

Conclusion: Cavity design had no influence on fracture resistance but in the failure pattern. Either glass ionomer or resin-composite can be used to substitute the dentin in vestibular cusps.