title: Comparison of survival time and comfort between 2 clear overlay retainers with different thicknesses: A pilot randomized controlled trial.
abstract: BACKGROUND
  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 = 0.111). The hazard ratio was 0.77 (95% CI, 0.48-1.24; P = 0.281). With regard to total failure rate, no statistical difference (P = 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 = 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.
  
  
  CONCLUSIONS
  Although the 0.75-mm group had a higher fracture rate, our results indicated no evidence that survival and comfort of retainers differ between 1.00 mm and 0.75 mm. When determining the type of retainer to be used, other factors such as retention effectiveness also should be considered.
  
  
  BACKGROUND
  This trial was registered at www.clinicaltrials.gov (NCT02618330).
  
  
  METHODS
  The protocol was not published before trial commencement.
authors.affiliation: Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Yafen
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Jianchang
authors.initials: J
authors.lastname: Lin
authors.affiliation: Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Hu
authors.initials: H
authors.lastname: Long
authors.affiliation: Department of Orthodontics, Ninth People's Hospital, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Niansong
authors.initials: N
authors.lastname: Ye
authors.affiliation: Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Renhuan
authors.initials: R
authors.lastname: Huang
authors.affiliation: Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Fan
authors.initials: F
authors.lastname: Jian
authors.affiliation: Department of Orthodontics, State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China. Electronic address: wenlilai@scu.edu.cn.
authors.forename: Wenli
authors.initials: W
authors.lastname: Lai
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002681:China; D004955:Esthetics, Dental; D005260:Female; D006801:Humans; D008297:Male; D016382:Orthodontic Appliance Design; D018704:Orthodontic Retainers; D017060:Patient Satisfaction; D010865:Pilot Projects; D016019:Survival Analysis