Load-induced Stresses in Photoelastic Primary Canines with Facial Restorations

Objectives: Abfractive forces have been shown to have deleterious effects on restorations of cervical lesions. It has been suggested that the stiffness of the restoration placed may play a role in their longevity. The purpose of this study was to photoelastically compare the stresses generated by loads on primary canines with facial restorations of different stiffness. Methods: Composite photoelastic models of a typical maxillary primary canine were fabricated using individual simulant materials for enamel, dentin, periodontal ligament, and alveolar bone. Models were made with identical facial preparations included either near the CEJ or at 2 mm incisally. The model teeth were restored using the following materials of disparate elastic moduli: a) high modulus, hybrid composite (Herculite XRV) and b) lower modulus compomer (Dyract). Three replications of each type of restored tooth were fabricated. Simulated masticatory forces were applied on the cusp tip and the cingulum of each tooth model. The resulting stress patterns were observed and recorded photographically in the field of a circular polariscope. Results: Prior to load application, similar low level polymerization induced shrinkage stresses were localized at the preparation margins of all models. Under both incisal and cingular loading, the higher modulus hybrid composite tended to concentrate stress along the gingival and proximal margins more than did the lower modulus compomer. This effect was more pronounced with cingular than with incisal loading. For both preparations and restoratives, higher stresses were produced by the cingulum loading. No significant differences were observed within each group of replicated restored models. Conclusions: These results suggest that, regardless of preparation height, lower modulus compomer restoration of facial lesions in primary maxillary canines may reduce stress production by abfractive forces.