Elastic Modulus Maturation Effect on Shrinkage Stress in a Primary Molar Restored with Tooth-Colored Materials.

Polymerization shrinkage stress is determined by shrinkage as well as elastic modulus. Elastic modulus develops during polymerization. This study evaluated how elastic modulus affects shrinkage stresses in a primary molar for three types of restorative materials. Elastic modulus of resin composite, compomers, and resin-modified glass ionomer (RMGI) were determined using four-point bending of rectangular beams at 10 minutes, 24 hours, and after one to four weeks storage in water (n equals 10). Results were analyzed using twoway analysis of variance and pairwise comparisons (α equals 0.05). The elastic moduli were used with published shrinkage data to calculate stresses at the tooth-restoration interface in finite element models of a cross-sectioned restored primary molar. The elastic modulus ranged between 5.6 to 19.9 gigapascal. Elastic modulus values were lowest at 10 minutes, regardless of material, and increased significantly (43 to 95 percent) in 24 hours; RMGI continued to increase (64 percent) for one week. Shrinkage stresses increased nonproportionally (resin composite 31 percent, compomer 35 percent, RMGI 52 percent) with increasing elastic modulus for sustained volumetric shrinkage. Elastic modulus development is material dependent and an important factor in polymerization shrinkage stress. Maturation of restorative materials can cause long-lasting stress increases if shrinkage is not alleviated by hygroscopic expansion.