Comparison of survival time and comfort between 2 clear overlay retainers with different thicknesses: A pilot randomized controlled trial
Am J Orthod Dentofacial Orthop 2017;151:433-9
The objective of this 2-arm parallel trial was to compare the survival times, failure rates, and comfort of 2 clear overlay retainers with different thicknesses (0.75 and 1.00 mm). Methods: Eighty eligible participants who had undergone orthodontic treatment at West China Stomatology Hospital of Sichuan University were recruited and randomly assigned to either the 0.75-mm group or the 1.00-mm group. Eligibility criteria included patients with central incisors, canines, and first molars and no systemic or oral disease. The main outcomes were survival time and total failure rate; the secondary outcomes were rates of different types of failure (fracture, loss, nonfitting, and abrasion); tertiary outcomes included patients’ comfort levels assessed with a visual analog scale and a health survey. Randomization was accomplished by tossing a coin, with the allocations concealed in sequentially numbered, opaque, sealed envelopes, and blinding implemented among practitioners, patients, and analysts. Patients were evaluated at 1, 3, 6, and 12 months of follow-up. Results: A total of 80 patients were initially recruited and randomized (42 in the 0.75-mm group, 38 in the 1.00-mm group); 72 patients completed the study and were analyzed (37 in the 0.75-mm group, 35 in the 1.00-mm group); there were 8 dropouts. Baseline characteristics were similar between the groups. At the end of the 1-year follow-up, survival time did not differ significantly between the groups (46.5 days; 95% confidence interval [CI], 10.3 -103.2; P 5 0.111). The hazard ratio was 0.77 (95% CI, 0.48-1.24; P 5 0.281). With regard to total failure rate, no statistical difference (P 5 0.118) existed between the 0.75-mm group (43.2%) and the 1.00-mm group (25.7%) (risk difference, 17.5%; 95% CI, 4.0%-39.1%). Among the different failure types, we found that fracture rates were significantly higher in the 0.75-mm group than in the 1.00-mm group (P 5 0.028), whereas other failure types were similar between the groups (all, P .0.05). No clinically significant differences were found in comfort between the 2 groups. No harms were encountered.