Influence of light transmittance and background reflectance on the light curing of adhesives used to bond esthetic brackets

Abstract

The objectives of this study were to determine the correlation between diffuse light transmittance (DLT) of esthetic brackets and the degree of cure (DC) of light-cured adhesives after direct irradiation, and to evaluate the influence of background reflectance. The influences of curing unit and irradiation time were also determined. The DLT of 4 ceramic and 4 plastic brackets was measured. Two reference light-curing protocols (cured over a glass slab; mean reflectance, 14.7%) and 4 experimental protocols (cured over bovine tooth slab; mean reflectance, 66.5%) were followed with 3 curing units: halogen, plasma arc, and light-emitting diode. The DC of 2 adhesives was calculated based on Fourier transform infrared spectroscopy. Two-way analysis of variance for the DC was performed (P = .05). The Pearson correlation between the DC and the DLT was determined. Mean DLTs were 44.9% to 75.9%. DC varied by bracket and curing protocol (P <.05) and also by adhesive. In the experimental protocols, there was no significant linear correlation between the DLT and the DC in both adhesives except 1 among 8 groups. The difference in reflectance of background influenced DC (P <.05). Based on this clinically simulated model, it was confirmed that the reflectance of the background tooth influenced the DC, instead of the DLT of a bracket. The interaction of the DLT and the reflectance of the background tooth on the light curing of adhesives should be studied further.