Comparative assessment of bonding time and 1-year bracket survival using flash-free and conventional adhesives for orthodontic bracket bonding: A split-mouth randomized controlled clinical trial

Introduction: A new flash-free adhesive promises to eliminate the flash removal step in bonding and to reduce bonding time by as much as 40% per bracket, with a bond failure rate of less than 2%. The aim of this trial was to compare bonding time and bracket failure rate over a 1-year period between the flash-free adhesive and a conventional adhesive for orthodontic bracket bonding. Methods: Forty-five consecutive patients had their maxillary incisors, canines, and premolars bonded with ceramic brackets (Clarity Advanced; 3M Unitek, Monrovia, Calif) using a flash-free adhesive (APC Flash-Free Adhesive Appliance System; 3M Unitek) on 1 side and a conventional adhesive (APCII Adhesive Appliance System; 3M Unitek) on the other side. The side allocation was randomized. Bonding was timed to the nearest second. Bond failure was recorded at standardized intervals of 4 weeks. The primary outcome was bonding time (average per tooth for each patient and per quadrant). Secondary outcomes were bracket failure rate within 1 year, time to first-time failure of a bracket, and bond failure type (adhesive remnant index score). Bonding times and adhesive remnant index scores upon bond failure were compared using paired t tests, with P <0.05 considered statistically significant. The adhesives were considered equivalent if the confidence interval for the difference between bracket failure rates fell within a margin of equivalence of ±5%. Results: The bonding times were significantly shorter with the flash-free adhesive than with the conventional adhesive, both per tooth (P <0.001) and per quadrant (P <0.001). Compared with the conventional adhesive, the average bonding times per tooth and per quadrant with the flash-free adhesive were 37.3% and 32.9% shorter, respectively. The bracket failure rates at 1 year were 3.7% for the flash-free adhesive and 0.9% for the conventional adhesive. This was statistically equivalent. The average times to first-time failure of a bracket were 25 weeks for the flash-free adhesive and 11 weeks for the conventional adhesive. Although there were no significant differences in the adhesive remnant index scores upon failure (P >0.05), the flash-free adhesive tended to fail more often at the enamel-adhesive interface than did the conventional adhesive. Conclusions: The use of the flash-free adhesive may result in bonding time savings of approximately one third compared with the conventional adhesive. With regard to bracket survival, a statistically significant difference was not found between the 2 adhesives when ceramic brackets were bonded. Registration: This trial was registered on December 3, 2013 (ClinicalTrials.gov ID, NCT02030002). Protocol: The protocol was not published before trial commencement.