Fracture resistance and stress distribution influenced by Load device types

Objective: This study analyzed the effect of different types of compressive load devices by means of a fracture resistance test on posterior teeth, stress distribution by finite elements and photoelastic analysis. Methods: Sixty-extracted-human-premolars with similar coronary-dimensions were used. Teeth-roots were embedded in polystyrene resin, simulating the periodontal ligament. Teeth received standardized MOD cavity preparations following restoration with composite resin (Esthetic X, Dentsply). The compressive test was carried out in a testing machine at a crosshead speed of 0.5mm/minute using 6 different metallic devices: G1- 2mm sphere, G2- 2mm cylinder, G3- device in knife ended form, G4 - 6mm sphere, G5- 6mm cylinder and G6- metal individualized antagonistic tooth, which contacted in centric relation of occlusion (1:1). Data were submitted to one-way ANOVA and Tukey test (p< 0.05). Modes of fracture were analyzed in a stereo-microscopic with 4X-magnification. Buccal-lingual mandible section performed exactly over the mesio-lingual cusps of the first maxillary premolar was computer designed, representing the enamel, dentin, periodontal ligament, spongy and cortical bone, cement and composite resin. An occlusal load was performed simulating each devices used in fracture test. The stress distribution was analyzed by a computer software, Ansys 6.1. A model of the maxillary premolar was fabricated in photoelastic material and the stress intensity and concentration was analyzed by numbers and clones of fringes. There were differences in the resistance and mode of fracture among the groups. Results: Fracture resistance were (Kgf): G3: 104.7±30.8a; G6: 92.8±21.6ab; G2:85.9±30.3ab; G1:82.7±33.2ab; G5:58.8±19.58bc; G4:46.13±15.7c. Conclusion: The stress distribution founded by photoelastic and FEA analysis is influenced by metallic device used to apply compressive load. Load applied under restoration result in higher fracture resistance values, however with longitudinal fracture of the dental elements.