Usefulness of orthodontic adhesive-containing fluorescent dye

Orthodontic adhesive is often left on the tooth surface when a multibracket appliance is debonded, and it is difficult to remove because its colour is similar to that of the tooth. If the adhesive changed colour during debonding, residual adhesive could be more easily removed. This in vitro study evaluated the usefulness of adhesive mixed with a small amount of fluorescent dye for clinical orthodontics. Sixty-four metal brackets were bonded to flattened bovine enamel surfaces using adhesives with three concentrations (0.001, 0.002, and 0.003 per cent) of fluorescent dye, and the shear bond strength (SBS) and adhesive remnant index (ARI) scores for each adhesive were determined. Colour penetrating through the transparent bracket was measured using a colour analyser. SBS and fluorescence intensity were examined to determine the stability of the adhesives after they were subjected to a thermal cycle test (1000 cycles). For data that were normally distributed, one-way analysis of variance followed by the Student-Newman-Keuls test was used to identify significant differences among the groups. If the data were not normally distributed, the Kruskal-Wallis H-test followed by the Mann-Whitney U-test with Bonferroni correction was used. Differences in ARI were determined with the chi-square test. The SBS of the adhesive with 0.003 per cent fluorescent dye was significantly lower than that of the control (Transbond). In ARI tests, significantly more of the adhesive with 0.003 per cent dye was left on the tooth surface after 24 hours compared with the other adhesives. With regard to colour penetration, the adhesive with 0.003 per cent dye was five times more visible than to others. SBS and fluorescence intensity of the adhesives were not affected by thermal cycling. Therefore, an adhesive containing less than 0.002 per cent fluorescent dye provides both sufficient bond strength for orthodontic brackets and sufficient fluorescent colour for easy visualization without aesthetic impairment.