ABSTRACT
AIM: With the development of the light-emitting diode (LED) to photo-activate composite resin, greater intensities could be reached without greater elevation of temperature in the mass of the composite resin and in the dental structure arisen from the irradiance in comparison to halogen equipments. This new scenario created a necessity to investigate the influence of temperature over the composite polymerization. MATERIALS AND METHODS: Several curing temperatures (Tcure- 0, 25, 50, 75, and 100°C) were used to polymerize a composite resin (Filtek Z250, 3M ESPE) for 40 and 60 s, using the halogen equipment Gnatus Optilight Digital (halogen) and two LEDs that use a new technology to assembly the diodes: LEC 1000 and bright LEC (MM Optics) (LED 1 and LED 2 respectively). The influence of curing temperature, added by the other variables studied, was evaluated using a methodology developed and improved at IFSC/USP, in which the penetration of a fluorescent dye in the body of the photopolymerized composite resin was quantified using fluorescence spectroscopy. RESULTS: According to the final data submitted to an analysis of variance, the presence of two groups of results could be verified: Between 0 and 25°C, both had a great percentage of the dye penetration compared with other Tcure with a variation in penetration from 69.26 ± 8.19% to 90.99 ± 3.38%. In this analysis, the effects of time and temperature were highly notable (p < 0.05) and the lesser value of dye penetration took place at 60 s of photoactivation This penetration was, in average, smaller with the Tcure of 25°C. The results showed that there was an interaction between the equipment and time and between time and temperature; the other group is regarding the Tcure was from 50, 75, and 100°C, despite the p = 0.05, the effect of temperature was notable. The penetration of the dye ranged from 8.87 ± 3.55 to 39.47 ± 8.9%. The effects of equipment and time were highly notable. The penetration with the time of 60 s was in average smaller. Except with the equipment LED 1, the percentages of the dye penetration were greater with the Tcure of 100°C. The smallest average was the Tcure of 50°C and 60 s of photoactivation. CONCLUSION: Based on the available data regarding the influence of curing temperature on the polymerization process of composite resins, was possible to concluded that small increments of heat increased the degree of conversion. We can assume that the energy supply through the generation of heat by the photopolymerizing devices can function as a heating medium for the reagent system by reducing its viscosity and increasing the mobility and agitation of its components. CLINICAL SIGNIFICANCE: The dentist must be aware of the effects that exist between the activation devices on the light output and their heat transmission to the composite and the tooth itself. This heat transmission might create a polymer with better characteristics.
