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.