Stress analysis of a bulk-filled Class V light-cured composite restoration

Clinical failures are often associated with the polymerization shrinkage of resin composite restorative materials. These problems include tooth sensitivity and fracture, marginal leakage, loss of the restoration, and recurrent decay. Our goal was to examine transient composite distortions and interface stresses as a bulk-filled light-cured composite polymerized in a Class V restoration. The analysis was based on a finite element model. The curing of the restoration was divided into 4 steps: approximately 1/30, 1/4, 1/2, and full depth (1/1) of cure. Since the actual curing pattern is not known, calculations were performed for three hypothetical (flat, convex, and concave) polymerization front shapes. The calculations showed that the assumed shape was a critical factor in determining cured surface deformations. For example, the initial cure depth (1/30) resulted in a surface bulge if the polymerization front was presumed convex, while the concave front resulted in a large intrusion. By the time that about 1/2 the depth of the restoration was cured, the differences were essentially gone. The final surface outline was intruded. Interface stresses in the curing restoration were qualitatively similar regardless of the assumed polymerization shape. As with surface distortions, the stresses changed with curing depth. It was concluded that (1) transient events during polymerization are possible contributors to clinical complications, and (2) more must be known about the polymerization pattern.