Do fluorescent agents alter the mechanical strength of orthodontic adhesives? An in vitro and clinical study

BACKGROUND: Fluorescent agents are added to orthodontic adhesives with the aim of making them visible under ultraviolet (UV) light, which ensures the complete, safe removal of remnants after orthodontic treatment. However, it is necessary to evaluate if the mechanical strength of these materials is maintained. Therefore, this study evaluated whether the addition of fluorescent agents influences the shear bond strength and clinical performance of a UV light-sensitive adhesive system. METHODS: This study consisted of two stages: (1) In vitro phase: 40 human teeth were selected, divided at random into 2 groups (n = 20), according to the adhesive system used: UV group—adhesive with fluorescent agent, and control group—conventional adhesive. A shear bond strength test was performed using a DL 2000 universal testing machine, at a speed of 0.5 mm/min. The accessories were removed and an evaluation of the Adhesive Remnant Index (ARI) was carried out. (2) Clinical phase: 8 patients were selected and had their appliances bonded using the split-mouth design (160 teeth) with the same tested adhesive systems (UV, n = 80; control, n = 80). The patients were monitored for bonding failure for a period of 24 months. Statistical analysis was performed using the Independent t test, chi-squared tests, and Mann-Whitney test, at a level of significance of 5% and confidence interval of 95%. RESULTS: Regarding the in vitro phase, the shear bond strength test yielded similar results in the two groups (p > 0.05) and the ARI showed statistically significant differences between the groups with a score of 1 being the most frequent ARI for both groups (70%). In addition, there was no clinical difference in terms of bonding failure between the groups (p > 0.05). CONCLUSION: The addition of fluorescent elements does not alter the mechanical strength and performance of the orthodontic adhesive and represents a viable alternative for clinical application.