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

Introduction: 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. Methods: 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. Results: 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). Conclusions: 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.