Effect of different light intensity of Quartz - Tungsten - Halogen light unit on the flexural strength of composite resin

Improvement of mechanical properties by increasing the degree of polymerization of composite resin is very important. As light intensity is a major factor in adequate polymerization, high intensity light units with decreased exposure time have been used. The aim of this study was to compare the effect of different light intensities on the flexural strength of composite resin. Methods & Materials: In this experimental study, 70 specimens of composite resin (Z100) were prepared by using stainless steel mold (25×2.5× 2mm). The composites were condensed into the mold, Mylar strip was put on them and they were irradiated with halogen light units under different exposure conditions. 1- 400mw/cm2 for 40S (control group). 2- 700mw/cm2 for 23S, 3- 1120 mw/cm2 for 14.3S, 4- 700 mw/cm2 for 40S, 5- 1120mw/cm2 for 10S, 6- 1120 mw/cm2 for 23S, 7- 1120 mw/cm2 in soft start method. Ten minutes after exposure, the specimens were taken out of the mold and after 24 hours storage in 37oC, they were inserted in Instron machine for three point bending test. ANOVA and Kruskal - wallis tests were used to determine the significant differences among the flexural strength means of all groups. The means of flexural strength of the seven groups were 122.52, 126.48, 133.71, 135.75, 123.21, 131.55 and 121.11 MPa. There was no significant difference among the means of flexural strength of the seven groups. Flexural strength of resin composite was insensitive to the rate of polymerization. Rapid polymerization with high light intensity during short exposure time had no adverse effect on flexural strength of resin composite.