ABSTRACT
This paper assesses the effects of light characteristics and irradiation time on the Vickers microhardness (VH) of a dual-photoinitiator commercial composite and on temperature increase in the pulp chamber (deltaT). Four recent light-emitting diodes (LEDs)--bluephaseG2 (BG2), bluephase16i (B16i), G-Light (G) and Freelight2 (F2)--and one control halogen light (XL3000-X) were tested on two shades of Tetric EvoCeram (A2 and Bleach XL), whose respective commercial formulations differed based on their concentration of camphorquinone and lucirin TPO. Three different irradiation times were applied--10, 20 and 40 seconds-and VH was measured on the upper and lower surfaces of 2-mm thick samples. The deltaT was measured by using a K-type thermocouple inserted into the pulp chamber of a molar that had been prepared to obtain a 2-mm thickness of dentin. The measurements were made either during polymerization of a 2 mm composite (Shade A2 or Bleach) or with an empty mold. The data were analyzed with the two-way ANOVA (p < 0.05) test. For shade A2, all but one irradiation condition (F2-10 seconds, lower surface) generated VH values that were statistically equal to or better than the standard chosen for this study (X-40 seconds). For Bleach shade, the VH values obtained with G and BG2-20 and 40 seconds were statistically comparable to X-40 seconds for both the upper and lower surfaces. This was not the case with either G and BG2-10 seconds or for all the procedures with other LCUs for which a VH of at least one of the surfaces was significantly lower than the reference. The results also highlight differences between the two material shades, whether the upper or lower surface is considered. Regarding temperature measurements for shade A2, B16i-20-40 seconds, BG2-40 seconds and G-40 seconds induced significantly higher deltaTs (3.98, 5.98, 5.21 and 4.95, respectively) than X-40 seconds (3.09). For Bleach shade, B16i-20 and 40 seconds, F2-20 and 40 seconds, BG2-40 seconds and G-40 seconds generated deltaTs significantly higher than the control values (2.70, 4.05, 3.03, 4.58, 2.74 and 2.44, respectively). The deltaT values obtained with uncovered tooth were generally higher than those obtained with a 2-mm layer of composite. In conclusion, this research emphasizes that a perfect correspondence between light and material spectra is of prime concern, both to insure optimal polymerization and to limit heating in the pulp chamber. Some reduction in curing time is possible, but only within certain limits.
