Composite conversion and temperature rise using a conventional, plasma arc, and an experimental blue LED curing unit Z. TARLE*, A. MENIGA*, A. KNEZ Ï EVIC  *, J. S Ï UTALO*, M. RISTIC  ² & G. PICHLER ³ *Department of Restorative Dentistry, School of Dental Medicine, University of Zagreb, Zagreb, Croatia, ² Rugjer Bos Ïkovic  Institute, Bijenic Ïka, Zagreb, Croatia and ³ Institute of Physics, Bijenic Ïka, Zagreb, Croatia SUMMARY SUMMARY The objective of this study was to evalu- ate the degree of conversion and temperature rise in three different composite materials when illumin- ated by an experimental light source [blue super- bright light emitting diodes LEDs)] and compared with plasma light and traditional photopolymeriza- tion unit. The degree of conversion and temperature rise were measured using Fourier transform infrared FTIR) spectroscopy and digital multimeter, respect- ively. The results revealed signi®cantly higher degree of conversion values in case of conventional curing than with other two light sources whereas temperature rise was signi®cantly lower when blue LEDs and plasma light were used. There were great differences in light intensities between blue LEDs of only 9 mW cm ±2 compared with plasma light of 1370 mW cm ±2 and Elipar II of 560 mW cm ±2 . Better match of LED spectral distribution peak to camphorquinone absorption distribution peak probably explains much lower intensities used for similar photopolymerization effect like in the case of rapid plasma lamp curing. KEYWORDS: KEYWORDS: composite photopolymerization, blue LEDs, plasma light Introduction Despite considerable improvements of dental composite materials, present-day composites still suffer from inad- equate degree of conversion and problems of marginal adaptation. Importance is attached to the development of new dentine bonding agents, chemistry of resins and ®llers rather than to any increase in intrapulpal tem- perature that occurs in composite resin placement from the material itself and from light-curing units Peutzfeldt, 1997; Stansbury et al., 1995; Meredith & Setchell, 1997). At present, the halogen lamp is the most often used light source for composite photopolymerization. How- ever, heat generation is a major disadvantage of using the halogen lamp as a light source Fujibayashi et al., 1998). A higher degree of conversion which is primarily related to curing light intensity and exposure time, con¯ict with the objective of achieving optimal margi- nal integrity because of the increased contraction Feilzer et al., 1995). Curing lights differ in intensity output and they range from < 200 to 1000 mW cm ±2 or more. Temperature rise during the curing of light activated restoratives relates both to the exothermic polymerization of the material and to the heat output from the dental light curing units and increases with increasing radiation time and decreased material thick- ness Lloyd et al., 1986). Masutani et al. 1988) conclu- ded that the resin itself had a greater in¯uence upon the temperature rise during the curing than the light source, whereas Strang et al. 1988) found the light activation unit as the most signi®cant source of heat during polymerization. Recent studies revealed that the marginal adaptation of light cured composites is enhanced when initial period of irradiation is conduc- ted at low light intensity Feilzer et al., 1990a). Very closely connected to temperature rise is polymerization shrinkage stress in the material which can be divided into the phases corresponding to the development of elastic modulus Sakaguchi et al., 1997). In the pre-gel phase, the composite is able to ¯ow, which relieves the ã 2002 Blackwell Science Ltd 662 Journal of Oral Rehabilitation 2002 29; 662±667