Effects of radiant exposure values using second and third generation light curing units on the degree of conversion of a lucirin-based resin composite

Abstract

Alternative photoinitiators with different absorption wavelengths have been used in resin composites (RCs), so it is crucial to evaluate the effectiveness of light-curing units (LCUs) on these products. Objective Using Fourier transform infrared analysis (FTIR) in vitro, the effects of varying radiant exposure (RE) values generated by second and third generation LED LCUs on the degree of conversion (DC) and maximum rate of polymerization (Rpmax) of an experimental Lucirin TPO-based RC were evaluated.Material and Methods 1 mm or 2 mm thick silicon molds were positioned on a horizontal attenuated total reflectance (ATR) unit attached to an infrared spectroscope. The RC was inserted into the molds and exposed to varying REs (18, 36 and 56 J/cm2) using second (Radii Plus, SDI) and third generation LED LCUs (Bluephase G2/Ivoclar Vivadent) or a quartz tungsten based LCU (Optilux 501/SDS Kerr). FTIR spectra (n=7) were recorded for 10 min (1 spectrum/s, 16 scans/spectrum, resolution 4 cm-1) immediately after their application to the ATR. The DC was calculated using standard techniques for observing changes in aliphatic to aromatic peak ratios both prior to, and 10 min after curing, as well as during each 1 second interval. DC and Rpmax data were analyzed using 3-way ANOVA and Tukey’s post-hoc test (p=0.05).Results No significant difference in DC or Rpmax was observed between the 1 mm or 2 mm thick specimens when RE values were delivered by Optilux 501 or when the 1 mm thick composites were exposed to light emitted by Bluephase G2, which in turn promoted a lower DC when 18 J/cm2 (13 s) were delivered to the 2 mm thick specimens. Radii Plus promoted DC and Rpmax values close to zero under most conditions, while the delivery of 56 J/cm2 (40 s) resulted in low DC values.Conclusions The third generation LCU provided an optimal polymerization of Lucirin TPO-based RC under most tested conditions, whereas the second generation LED-curing unit was useless regardless of the RE.

Influence of Light-curing Units on Surface Microhardness and Color Change of Composite Resins after Challenge

“…2 The literature has shown studies where composites were manipulated in the laboratory to quantify photoinitiators and standardize the composite resin samples. 2,3,8,10,22,23 However, this does not match what the dentist experiences every day in the office, demonstrating the high clinical relevance of the present study by using resins commonly found in the dental market.…”

“…The study conducted by Michaud et al 18 compared the irradiance and the distribution of the wavelengths of LCUs of different generations, concluding that poly-wave LEDs have an inhomogeneous irradiance profile. Furthermore, Cardoso et al 8 suggested that the wavelength emitted by the single-wave LEDs covers a narrow part of the Lucirin-TPO absorption wavelength; it is possible that the use of a high radiant emittance for a longer period of time may have led to the delivery of higher radiance exposure values within the narrow wavelength range capable of exciting Lucirin-TPO. In this study, based on the time and power for each apparatus, the irradiance values were concluded as 48 J/cm 2 for the single-wave LUC and 40 J/cm 2 for the poly-wave LCU.…”

“…2,3 This feature permits the curing of resin materials even when different photoinitiators are used in their compositions. 2,7,8 The literature is scarce in studies evaluating the microhardness and color change of commercial composite resins when using LEDs with multiple wavelengths.…”

Interaction between photoactivators and adhesive systems used as modeling liquid on the degree of conversion of a composite for bleached teeth

“…Due to their short emission spectrum, second-generation LEDs may not activate some alternative photoinitiators present in the composite [6,8], consequently compromising the polymerization reaction and decreasing the DC.…”

“…However, despite monowave LEDs emitting high light intensity, they do not enable adequate polymerization of some photoinitiators and alternative co-initiators [6][7][8], thereby potentially causing problems in the polymerization reaction. Alternative photoinitiators such as (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TPO) and bis-alkyl phosphinic oxide (BAPO) have been replacing camphorquinone (CQ) in some composites to reduce the yellowing effect caused by CQ [9].…”