Objective This study assessed the development of stress from polymerization of light-cured dental resin composites for 24 hours after irradiation. Materials and Methods Initial cracks were made near the edge of a cylindrical hole in glass, and crack lengths were measured. Revolution Formula 2, Kalore and Venus Diamond were polymerized in the hole. Crack lengths were measured at several intervals after irradiation up to 24 hours. Stresses at the composite-glass interface were calculated using the crack lengths. Elastic moduli of the composites were measured at the same time intervals. Results Interfacial stress and elastic modulus were significantly related to material and time. Stress continued to increase up to 12 hours after irradiation. Significantly lower stresses were measured in Kalore and Venus Diamond than Revolution Formula 2 throughout 24 hours. Stress at 24 hours was two times greater than the stress at 30 minutes. The increase in elastic modulus from 30 minutes to 24 hours ranged from 8 to 24%, which was less than the increase in stress over the same time period. Conclusions Interfacial stress and elastic modulus of the composites demonstrated the average increases of 155% and 14%, respectively, from 30 minutes to 24 hours after irradiation. Clinical Significance Since the elastic modulus is a measure of stiffness and resistance to load, clinicians might consider advising their patients to avoid heavy occlusal function until the elastic modulus has reached a plateau, which would be 60 minutes for Venus Diamond, 12 hours for Kalore, and 24 hours for Revolution Formula 2.
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