This study evaluated changes in optical properties during light-curing of resin-composites containing different photo-initiators. Five experimental resin-composites containing different photo-initiators were light cured and measurements were taken of light transmittance, color, translucence, and degree of conversion before and after curing. The increases in light transmittance and translucence during curing varied significantly depending on the photo-initiator, with composites containing camphorquinone showing the highest increases, likely due to its photo-bleaching effect. While degree of conversion also varied between photo-initiators, it did not directly correlate with changes in optical properties.

1. Dayane Oliveira
Oregon Health and Science University
Department of Dental Materials
e-mail: oliveira.day@icloud.com
Changes in Optical Properties During Light-curing of Resin-composites Containing Different Photo-initiators
Dayane Oliveira*, Mario Coelho Sinhoreti & Jack Liborio Ferracane
Objectives: The aim of this study was to evaluate the change in optical properties during light-curing of resin-composites containing
different photo-initiators.
Materials and Methods: Five experimental resin-composites with the same resin blend/filler loading and containing different photo-
initiators (CQ+DMAEMA; PPD; PPD+DMAEMA; TPO or BAPO) were light-cured in 1mm thick Delrin disks (φ=6mm; n=3) with the
bottom surface placed over the sensor of a MARC Resin Calibrator to measure light-transmittance (TT). Color measurements were
taken over white and black backgrounds using a pre-calibrated chromameter (CR-221) before and after light-curing. Two LEDs (Radii:
λ=420–540nm and Bluephase G2: λ=380-420nm+420-540nm) were used with same irradiance (1300mW/cm
2
) for 30s. CIE L*a*b* and
CIExyY systems were used to access color and translucence (TP) changes, respectively. To assess DC, a FT-IR spectrometer (Nicolet
6700) was used to measure the non-polymerized and post-polymerized blends after photo-polymerization using near-IR analysis. Data
were analyzed by ANOVA and Tukeyʼs test for multiple comparisons (α=0.05).
Results: Increases in TT during light-curing varied significantly with photo-initiator type: CQ+DMAEMA (87-131%: from 225 to
550mW/cm
2
) > PPD (26-51%: 400-600mW/cm
2
) > PPD+DMAEMA (20-37%: 410-565mW/cm
2
) > BAPO (15-24%: 440-660mW/cm
2
) >
TPO (8-18%: 460-575mW/cm
2
), as shown in Figure 1. Increases in TP also varied with the photo-initiators: BAPO (5%: from 8 to 13%)
> CQ+DMAEMA (4%: 9%-14%) = TPO (4%: 8-13%) > PPD (1.5%: 8-12%) > PPD+DMAEMA (1%: 10-11.5%), as shown in Figure 2.
These increases were not directly related to differences in DC (CQ: ~60%; PPD: ~12%; PPD+DMAEMA: ~50%; TPO: 3-68%; BAPO:
50-69%, as shown in Figure 3), which would increase the refractive index match between the resin/filler during curing. The greater
change for CQ seems to be related to the effect of photo-bleaching shown by Δb (CQ: -19; PPD: -6; PPD+DMAEMA: -10; BAPO: -7;
TPO: -3, as shown in Figure 4).
Conclusions: Within the limitations imposed by the experimental design used in this study, the following conclusions can be drawn: 1-
TT and TP increased during curing regardless of the photo-initiators or the light-curing unit evaluated; 2- Resin composites containing
CQ showed higher TT and TP increases during light-curing compared to the other photo-initiators evaluated, especially when light-
curing with the 420-540nm range exclusively due to photo-bleaching effect.