Comparison of bonding failure rates of mandibular retainers after 2 enamel preparations - sandblasting vs pumicing: An 18-month randomized controlled trial.

Introduction: Several protocols have been suggested in the literature to bond fixed retainers without a clear emerging consensus. This study aimed to compare, over 18 months, the bonding failure rate of mandibular canine-to-canine Zachrisson-type retainer after either sandblasting or pumicing the enamel surface before bonding.

Methods: Ethical approval was obtained. Patients about to enter their retention phase were recruited from October 2019 to January 2021 at the local University hospital. Patients were block-randomized either in the 50 μm aluminum oxide particles sandblasting group (experimental) or the pumicing group (control). Eligibility criteria included minimal age of 11, presence of all mandibular incisors and canines, no active carious lesion, no restoration nor periodontal disease. All wires were bonded by the same operator. The primary outcome was any first-time retainer bonding failure, recorded by 2 assessors at 3, 6, 9, 12, 15, and 18 months after bonding. Wire fractures and unexpected adverse movements were registered as secondary outcomes. The randomization sequence was generated via the CleanWeb platform (Telemedicine Technologies S.A.S, Paris, France) by blocks of variable size. Assessors and statisticians were blinded to group assignments. Groups were compared with Pearson's χ test. A Kaplan-Meier survival analysis was performed, and groups were compared with a log-rank test.

Results: Eighty-eight patients (mean age, 16.5 years; interquartile range, 3 years) were recruited, and 44 patients were randomized into each group. Eighty-two patients (experimental, 38; control, 44) were finally analyzed. At 18 months, the number of first-time bonding failures was respectively 3/38 (7.9%) and 11/44 (25.0%) among the sandblasting and pumicing groups (Pearson's χ test, P = 0.04). Relative risk with a 95% confidence interval was 0.32 (0.10-0.96). The 18-month survival 93% rate in the sandblasting group was significantly different from the 75% rate in the pumicing group (log-rank test, P = 0.02). No wire fracture was recorded during this 18-month follow-up. No serious harm was observed except for some unexpected adverse dental movements in 7.1% of patients.

Conclusions: Enamel sandblasting leads to a statistically and clinically significant 3-fold reduction in the bonding failure rate of mandibular bonded retainers compared with simple pumicing.

Registration: The trial was registered on ClinicalTrials.gov ID NCT03954145.

Protocol: The protocol was not published before trial commencement.

Funding: No funding or conflict of interests to be declared.