Comparison of Depth of Cure, Hardness and Heat Generation of LED and High Intensity QTH Light Sources Sayed Mostafa Mousavinasaba Ian Meyersb AbstrAct Objectives: To compare curing performance of a second generation LED curing light with a high power tungsten quartz halogen (QTH). Methods: A hybrid composite resin (Filtek Z 250, 3M, USA) was used as test material and cured using a second generation LED light (Translux Power BlueTM, Heraus Kulzer ,Germany) or a very high power QTH light unit (EMS, Switzerland). A two split aluminum mold was used to prepare ten samples with LED light source cured for forty seconds and ten samples prepared using high power QTH light unit, cured for four or six seconds recommended exposure time. Hardness, depth of cure (DOC) and thermal rise during exposure time by these light sources were measured. The data sub- mitted to analysis of variance (ANOVA), Tukey's and student's t tests at 5% significance level. Results: Significant differences were found in hardness, DOC of samples cured by above men- tioned light sources and also in thermal rises during exposure time. The curing performance of the tested QTH was not as well as the LED light. TPB light source produced the maximum hardness (81.25, 73.29, 65.49,55.83 and 24.53 for 0 mm, 1 mm, 2 mm, 3 mm and 4 mm intervals) and DOC (2.64 mm) values with forty seconds irradiation time and the high power (QTH) the least hardness (73.27, 61.51 and 31.59 for 0 mm, 1 mm and 2 mm, respectively) and DOC (2 mm) values with four seconds irradiation time.Thermal rises during 4 s and 6 s curing time using high power QTH and tested LED were 1.88˚C, 3˚C and 1.87˚C, respectively. Conclusions: The used high power LED light produced greater hardness and depth of cure dur- ing forty seconds exposure time compared to high power QTH light with four or six seconds curing time. Thermal rise during 6 s curing time with QTH was greater compared to thermal changes oc- curred during 40 s curing time with tested LED light source. There was no difference seen in thermal changes caused by LED light with 40 s and QTH light with 4 s exposure time. (Eur J Dent 2011;5:299- 304) Key words: Hardness; Depth of cure; Resin composite; Heat generation. a Associate Professor, Department of Restorative Dentistry,Torabinejad Research Dental Center, School of Dentistry, Isfahan University of Medical Sciences and Health Services, Isfahan, Iran. b Professor, Colgate Chair of General Practice Dentistry,The University of Queensland, Brisbane, Australia. Corresponding author: Sayed Mostafa Mousavinasab Department of Restorative Dentistry, Torabinejad Research Dental Centre, School of Dentistry, Isfahan University of Medical Sciences and Health Services, Isfahan, Iran. Phone: +98 311 7922849 Fax : +98 311 6687080 E-mail: S_mousavinasab@dnt.mui.ac.ir July 2011 - Vol.5 299 European Journal of Dentistry