The aim of this study was to investigate the effect of light irradiation modes on polymerization shrinkage, degree of cure and microleakage of a composite resin.

VIP™ (Bisco Dental Products, Schaumburg, IL, USA) and Optilux 501™ (Demetron/Kerr, Danbury, CT, USA) were used for curing Filtek™ Z-250 (3M Dental Products, St. Paul., MN, USA) composite resin using following irradiation modes: VIP™ (Bisco) 200mW/cm² (V2), 400mW/cm² (V4), 600mW/cm² (V6), Pulse-delay (200 mW/cm² 3 seconds, 5 minutes wait, 600mW/cm² 30seconds, VPD) and Optilux 501™ (Demetron/Kerr) C-mode (OC), R-mode (OR).

Linear polymerization shrinkage of the composite specimens were measured using Linometer (R&B, Daejeon, Korea) for 90 seconds for V2, V4, V6, OC, OR groups and for up to 363 seconds for VPD group (n=10, each).

Degree of conversion was measured using FTIR spectrometer (IFS 120 HR, Bruker Karlsruhe, Germany) at the bottom surface of 2 mm thick composite specimens. V2, V4, V6, OC groups were measured separately at five irradiation times (5, 10, 20, 40, 60 seconds) and OR, VPD groups were measured in the above mentioned irradiation modes (n=5, each).

Microhardness was measured using Digital microhardness tester (FM7, Future-Tech Co., Tokyo, Japan) at the top and bottom surfaces of 2mm thick composite specimens after exposure to the same irradiation modes as the test of degree of conversion(n=3, each).

For the microleakage test, class V cavities were prepared on the distal surface of the ninety extracted human third molars. The cavities were restored with one of the following irradiation modes: V2/60 seconds, V4/40 seconds, V6/30 seconds, VPD, OC and OR. Microleakage was assessed by dye penetration along enamel and dentin margins of cavities.

Mean polymerization shrinkage, mean degree of conversion and mean microhardness values for all groups at each time were analyzed using one-way ANOVA and Duncan's multiple range test, and using chi-square test for microleakage values.

The results were as follows:

·Polymerization shrinkage was increased with higher light intensity in groups using VIP™ (Bisco): the highest with 600mW/cm², followed by Pulse-delay, 400mW/cm² and 200mW/cm² groups. The degree of polymerization shrinkage was higher with Continuous mode than with Ramp mode in groups using Optilux 501™ (Demetron/Kerr).

·Degree of conversion and microhardness values were higher with higher light intensity. The final degree of conversion was in the range of 44.7 to 54.98% and the final microhardness value in the range of 34.10 to 56.30.

·Microleakage was greater in dentin margin than in enamel margin. Higher light intensity showed more microleakage in dentin margin in groups using VIP™ (Bisco). The micoleakage was the lowest with Continuous mode in enamel margin and with Ramp mode in dentin margin when Optilux 501™(Demetron/Kerr) was used.