Light-curing Characteristics of a Resin Composite

OBJECTIVE: To compare the cure profiles and depth of cure in simulated class II cavities with those found using cylindrical molds and unrestricted blocks of composite. METHODS: A resin composite (Z100/A3.5) was placed in one increment and light-cured in simulated class II cavities with a metal matrix band; in 6.0 mm stainless steel molds; and in 22 mm molds to allow unrestricted curing. All light curing was carried out at a power density of 620 mW/cm2 and 20 s cure time. After 24 hours, specimens were removed and uncured material scraped away. Specimens were polished to expose longitudinal surfaces at mid-plane and Knoop hardness (KHN) measurements were made across these surfaces. These results were used to construct iso-hardness profiles and KHN vs depth profiles. Cure depth, DC, was defined as the axial depth having 80% of maximum KHN. RESULTS: The DC for the unrestricted composite was directly related to the diameter of the light-guide and at 7.0 mm the DC was 3.6 mm and was statistically different (p= 0.05) from the DC for the cylinders, 3.3 mm. For the simulated cavities the DC was 2.8 mm, which was statistically different from the other two groups. Diiferences in cure profiles were found with varying light-guide size and due to constraining walls for the cylinders and cavity boundaries. CONCLUSIONS: Depth of cure is affected by both the size of the light-guide and composite mass and by physical barriers constraining the composite.