Mousavinasab, Meyers reducing the ability of irradiated light to increase temperature. This has been shown by a study in which the temperature rise caused by irradiation was less via a previously cured composite than via an initially unpolymerized composite.39 According to the results of this study, compos- ite increments less than 2 mm in thickness should be cured using a high power QTH light source for a short period of time, especially in deep cavities to ensure proper curing of the composite. Applying thicker increments and increasing the exposure time to compensate will increase temperature rise and endanger pulp chamber vitality. ocnLusIons • Hardness values produced were greater with the LED light than with the QTH light. • Depth of cure obtained was higher with the LED light. • Depth of cure produced by the QTH light was higher for a recommended 6 s irradiation than for a shorter 4 s exposure. • Thermal changes were greater using the QTH light for 6 s than using it for 4 s or the LED light for 40 s. • Thermal changes were the same whether us- ing the LED light for 40 s or the QTH light for 4 s. rEFErEncEs 1. Mills RW, Uhl A, Jandt KD. Optical power outputs, spectra and dental composite depths of cure, obtained with blue light emitting diode (LED) and halogen light curing units (LCUs). Br Dent J 2002;193:459-463. 2. Dunn WJ, Bush AC. A comparison of polymerization by light-emitting diode and halogen-based light-curing units. J Am Dent Assoc 2002;133:335-341. 3. Soh MS, Yap AU, Siow KS. Effectiveness of composite cure associated with different curing modes of LED lights. Oper Dent 2003;28:371-377. 4. Uhl A, Mills RW, Vowles RW, Jandt KD. Knoop hardness depth profiles and compressive strength of selected dental composites polymerized with halogen and LED light curing technologies. J Biomed Mater Res 2002;63:729-738. 5. Uhl A, Mills RW, Jandt KD. Photoinitiator dependent com- posite depth of cure and Knoop hardness with halogen and LED light curing units. Biomaterials 2003;24:1787-1795. 6. Mills RW, Uhl A, Blackwell GB, Jandt KD. High power light emitting diode (LED) arrays versus halogen light polym- erization of oral biomaterials: Barcol hardness, compres- sive strength and radiometric properties. Biomaterials 2002;23:2955-2963. July 2011 - Vol.5 7. Wiggins KM, Hartung M, Althoff O, Wastian C, Mitra SB. Curing performance of a new-generation light-emitting diode dental curing unit. J Am Dent Assoc 2004;135:1471- 1479. 8. Tseng WY, Chen RS, Wang JL, Lee MS, Rueggeberg FA, Chen MH. Effects on microstrain and conversion of flow- able resin composite using different curing modes and units. J Biomed Mater Res B Appl Biomater 2007;81:323-329. 9. Knezevic A, Tarle Z, Meniga A, Sutalo J, Pichler G, Ristic M. Degree of conversion and temperature rise during polym- erization of composite resin samples with blue diodes. J Oral Rehabil 2001;28:586-591. 10. Hofmann N, Hugo B, Klaiber B.Effect of irradiation type (LED or QTH) on photo-activated composite shrinkage strain kinetics, temperature rise, and hardness. Eur J Oral Sci 2002;110:471-479. 11. Ozturk B, Ozturk AN, Usumez A, Usumez S, Ozer F. Tem- perature rise during adhesive and resin composite po- lymerization with various light curing sources. Oper Dent 2004;29:325-332. 12. Weerakoon AT, Meyers IA, Symons AL, Walsh LJ. Pulpal heat changes with newly developed resin photopolymeri- sation systems. Aust Endod J 2002;28:108-111. 13. Knezevic A, Tarle Z, Meniga A, Sutalo J, Pichler G. Influence of light intensity from different curing units upon compos- ite temperature rise. J Oral Rehabil 2005;32:362-367. 14. Tarle Z, Knezevic A, Demoli N, Meniga A, Sutaloa J, Unter- brink G, Ristic M,Pichler G. Comparison of composite cur- ing parameters: effects of light source and curing mode on conversion, temperature rise and polymerization shrink- age. Oper Dent 2006;31:219-226. 15. Guiraldo RD, Consani S, Lympius T, Schneider LF, Sinho- reti MA, Correr-Sobrinho L. Influence of the light curing unit and thickness of residual dentin on generation of heat during composite photoactivation. J Oral Sci 2008;50:137- 142. 16. Hannig M, Bott B. In-vitro pulp chamber temperature rise during composite resin polymerization with various light- curing sources. Dent Mater 1999;15:275-281. 17. Asmussen E, Peutzfeldt A. Temperature rise induced by some light emitting diode and quartz-tungsten-halogen curing units. Eur J Oral Sci 2005;113:96-98. 18. Aravamudhan K, Floyd CJ, Rakowski D, Flaim G, Dickens SH, Eichmiller FC, Fan PL. Light-emitting diode curing light irradiance and polymerization of resin-based com- posite. J Am Dent Assoc 2006;137:213-223. 19. Hasler C, Zimmerli B, Lussi A. Curing capability of halogen and LED light curing units in deep class II cavities in ex- tracted human molars. Oper Dent 2006;31:354-363. 303 European Journal of Dentistry