Do we need primer for orthodontic bonding? A randomized controlled trial

Objective: To evaluate the clinical performance of APC (TM) II Victory Series (TM) (3M Unitek) brackets in direct orthodontic bonding with and without the use of primer. Design: A single-operator, two-centre prospective, non-inferiority randomized controlled clinical trial. Setting: The Orthodontic departments at the Leeds Dental Institute and St Luke's Hospital, Bradford, UK. Ethical approval: Ethical approval was granted by Leeds (East) Research Ethics Committee on 18th of December 2009 (Reference 09/H1306/102). Protocol: The protocol was not published prior to trial commencement. Subjects and methods: Ninety-two patients requiring orthodontic treatment with fixed appliances were randomly allocated to the control (bonded with primer) or test groups (bonded without primer). Patients were randomly allocated to either the control or experimental group. This was performed by preparing opaque numbered sealed envelopes in advance using a random numbers table generated by a computer by an independent third party. Once the envelopes were opened, blinding of the operator and the patient was no longer possible due to the nature of the intervention. Patients were approached for inclusion in the trial if they qualified for NHS orthodontic treatment requiring fixed appliances and had no previous orthodontic treatment. Main outcome measures: Number of bracket failures, time to bond-up appliances, and the adhesive remnant index (ARI) when bracket failure occurred, over a 12-month period Results: Failure rate with primer was 11.1 per cent and without primer was 15.8 per cent. Bonding without primer was shown statistically to be non-inferior to bonding with primer odds ratio 0.95-2.25 (P = 0.08). Mean difference in bond-up time per bracket was 0.068 minutes (4 seconds), which was not statistically significant (P = 0.402). There was a statistically significant difference in the Adhesive Remnant Index - ARI 0 with primer 49.4 per cent, no primer 76.5 per cent, (P < 0.0001). Limitations: As the study was only performed by one operator, the results can therefore only be truly be applied to their practice. Also this study was powered to ascertain if there was no difference between the 2 groups up to 5%, however orthodontists may consider a change in the bracket failure rate of 2% to be clinically significant. Conclusion: When bonding with APC (TM) II Victory Series (TM) brackets without primer was shown statistically to be non-inferior to bonding with primer (P = 0.08). There was no significant difference in bond-up times. Bond failure was more likely to happen at the composite-enamel interface when bonded without a primer.