How cavity dimension influences in the composite deformation during polymerization shrinkage

Abstract

PURPOSE: To understand how the dimensions of the cavity made of a rigid substrate influences on displacement of the composite free surface during polymerization shrinkage. MATERIAL AND METHODS: Cylindrical cavities in 4 or 6mm diameter and 1 or 2mm depth were prepared in glass rods. These cavities were restored in bulk (Single Bond + Filtek Z250). Free surface displacement was monitored for 10 minutes with a probe. The data was analyzed 60 seconds and 10 minutes after photo-activation. Results were analyzed using two-way ANOVA/Tukey’s test to evaluate the influence of diameter and depth, and Student’s t-test to compare the periods (α=0.05). RESULTS: The interaction between the factors diameter and depth was statistically significant (p<0.05 for both periods), but Tukey’s test did not revealed this interaction. For the same diameter the higher the cavity depth, the higher was the displacement. Student’s t-test showed that the displacement was significant higher at 10 minutes than at 60 seconds (p<0.05), even though this difference was not so evident numerically. It was not possible to determine any strong correlation with volume neither with C-factor. CONCLUSIONS: The displacement of free surface represents the stress state to which the composite is subjected. The variation in depth of the cavity seems to be a further factor that influences the displacement of free surface, more than variation in diameter.