Cusp Deflection in Class V Cavities Restored with Composites

Objectives: The purpose of this study was to evaluate the effect of the polymerization shrinkage and modulus of elasticity of composites on the cusp deflection of class V restoration in premolars. Methods: The 16 extracted upper premolars were divided into two groups with similar size. V-shaped class V cavities with a dimension of 3 mm height and 2 mm depth were prepared. The cavities were treated using the total etching with 35% phosphoric acid and single bond (3M) adhesive. The amounts of cusp deflection were measured when the Class V cavities were restored with a flowable composite (Filtek flow) or a universal hybrid composite (Z-250) using a LVDT displacement sensor. After the measurement of cusp deflection, the bonded interfaces of the sectioned specimens were observed using a scanning electron microscopy (SEM). The polymerization shrinkage and modulus of elasticity of the composites were measured to investigate the effect of physical properties of composites on the cusp deflection. The data were analyzed with student's t-test at a significant level p=0.05. Results: The amounts of cusp deflection restored with Filtek flow or Z-250 were 2.18±0.92 µm and 2.95±1.13 µm, respectively. There was no statistically significant difference (p>0.05). The two specimens in each group showed gap in the inner portion of the cavity. The polymerization shrinkage of Filtek flow (4.41±0.10%) was higher than that of Z-250 (2.23±0.14%), but the modulus of elasticity of Filtek flow (7.77±0.87 GPa) was much lower than that of Z-250 (17.43±0.10 GPa). Conclusion: The cusp deflection depends not only on the polymerization shrinkage but also on the modulus of elasticity of composites.