Background/purpose: Polymerization contraction stress is an undesirable and inevitable characteristic of adhesive restorations. It is important to understand the stress distribution to improve the clinical effectiveness of resin composite restoration. The aim of this study was to evaluate the polymerization shrinkage stress created in tooth photoelastic models using different filling techniques. Materials and methods: Twenty Class II tooth models were obtained. They were distributed into four

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... perimental groups (n Z 5) according to the following restorative techniques: resin composite with horizontal insertion, resin composite with oblique insertion, flowable composite þ resin composite with horizontal insertion, and flowable composite þ resin composite with oblique insertion restoration. Restored photoelastic models were analyzed using a plane polariscope. The stress along seven points of adhesive interface was analyzed from images of each insertion, at the baseline (immediately) and 24 hours after polymerization. Maximum shear stress data were obtained and submitted to two-way ANOVA analysis followed by Tukey's posthoc test at P Z 0.05. Results: Horizontal and oblique techniques have shown differences in stress patterns. No difference between stress values of horizontal and oblique techniques was found. Groups restored with flow composite showed significant higher stress levels than those restored only with universal composite. Conclusion: The use of flow composite created higher polymerization stress effects on the class II restoration than does the conventional restoration technique.