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.
Highlights
In an attempt to meet patients’ growing needs for aesthetic satisfaction, clinicians are frequently using teeth whitening techniques with their patients
Given that camphorquinone (CQ), the most common photoinitiator used in lightcured resin composites (RCs), has a bright yellow pigment that can interfere with the resin’s color when lighter shades are required[5,27], lighter alternatives such as 1-Phenyl 1-2propanedione (PPD) or Lucirin TPO are being added to composite formulations[9,18]
This study aimed to evaluate the influence of the radiant exposure (RE) and light-curing units (LCUs) type on the degree of conversion (DC) and maximum rate of cure (Rpmax) of experimental composite resin containing only Lucirin TPO
Summary
In an attempt to meet patients’ growing needs for aesthetic satisfaction, clinicians are frequently using teeth whitening techniques with their patients. In order to keep up with this new trend, manufacturers have developed resin composites (RCs) with relatively unsaturated shades and a translucency to match bleached teeth. Given that camphorquinone (CQ), the most common photoinitiator used in lightcured RCs, has a bright yellow pigment that can interfere with the resin’s color when lighter shades are required[5,27], lighter alternatives such as 1-Phenyl 1-2propanedione (PPD) or Lucirin TPO are being added to composite formulations[9,18]. The first and second generations of light emitting diode (LED) light curing units (LCUs) used in dentistry emit blue light in a narrow wavelength between 410 and 470 nm. They are unable to properly cure resin materials in which the CQ has been partially replaced with alternative photoinitiators[9,23,30]
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