Effect of light activation method on flexural properties of dental composites

Purpose: To determine if irradiating composites in a laboratory tungsten-halogen light-curing unit produced equal flexural properties to stepwise hand-curing with a tungsten-halogen lamp. Methods: Bars (n=10) of nine commercial composites were formed by light-curing in square glass tubes (2 x 2 x 25 mm). Flexure strength (FS, MPa) and flexure modulus (FM, GPa) were tested in three-point bending after aging specimens in water at 37°C for 1 day. Two methods were used to irradiate the composites: a) Triad II (Dentsply) using 40-second exposures from top and bottom; and b) Optilux 400 (Demetron; 600 mW/cm²) using 3 x 40 seconds overlapping exposures from the top only. Filler wt% was determined by thermal gravimetric analysis. The degree of conversion (DC) of each composite cured with the two techniques was evaluated by micro-FTIR. T-tests were performed for FS and FM to compare Triad II vs Optilux for each composite (α< 0.05). Results: There was a trend for Optilux to produce greater FS (significant for A110, Herculite and P60) and FM (significant for all but Clearfil, Esthet-X and Z250), but differences averaged less than 10%. There was no difference in DC between the irradiation modes for any composite.