Detection of residual resin-based orthodontic adhesive based on light-induced fluorescence

Introduction: This study evaluated the fluorescence of orthodontic adhesives using quantitative light-induced fluorescence–digital (QLF-D) images, and compared differences in the color characteristics of the fluorescence between adhesive and the adjacent tooth with that under white-light illumination in specimens containing residual adhesive of various thicknesses. Methods: Disc-shaped adhesive samples and samples comprising adhesive attached to extracted human teeth were prepared using Transbond XT, Blugloo, and Enlight, and they were ground to thicknesses ranging from 800 to 20 μm. Fluorescence and white-light images of the two types of specimens were taken with a QLF-D system. The color parameters for the fluorescence from the discs and the color difference (ΔE) between residual adhesive and the adjacent tooth were quantified in images using the CIE L*a*b* system. Results: The fluorescence color values of the discs differed significantly among the three adhesive products (P < 0.05). The ΔE values in fluorescence (ΔE _F ) and white-light (ΔE _W ) images for all three adhesives were lower for thinner residual adhesive specimens. The thickness of the adhesive could be perceived over a range of 50–100 μm for fluorescence images and 400–800 μm for white-light images (ΔE > 3.3). ΔE _F was significantly larger than ΔE _W for all of the residual adhesives, Blugloo specimens thicker than 100 μm, and Transbond XT and Enlight specimens thicker than 50 μm (P < 0.05). Conclusions: Detecting and analyzing fluorescence signals can improve the ability to detect residual adhesive on a tooth and also provide thickness information.