title: Survival of bonded lingual retainers with chemical or photo polymerization over a 2-year period: a single-center, randomized controlled clinical trial.
abstract: BACKGROUND
  The objective of this trial was to compare the survival rates of mandibular lingual retainers bonded with either chemically cured or light-cured adhesive after orthodontic treatment.
  
  
  METHODS
  Patients having undergone orthodontic treatment at a private orthodontic office were randomly allocated to fixed retainers placed with chemically cured composite or light-cured composite. Eligibility criteria included no active caries, restorations, or fractures on the mandibular anterior teeth, and adequate oral hygiene. The main outcome was any type of first-time lingual retainer breakage; pattern of failure (adapted adhesive remnant index scores) was a secondary outcome. Randomization was accomplished with random permuted blocks of 20 patients with allocation concealed in sequentially numbered, opaque, sealed envelopes. Blinding was applicable for outcome assessment only. Patients were reviewed at 1, 3, and 6 months and then every 6 months after placement of the retainer until completion of the study. Data were analyzed using survival analysis including Cox regression; sensitivity analysis was carried out after data imputation for subjects lost to follow-up.
  
  
  RESULTS
  Two hundred twenty patients (median age, 16 years; interquartile range, 2; range, 12-47 years) were randomized in a 1:1 ratio to either chemical or light curing. Baseline characteristics were similar between groups, the median follow-up period was 2.19 years (range, 0.003-3.64 years), and 16 patients were lost to follow-up. At a minimum follow-up of 2 years, 47 of 110 (42.7%) and 55 of 110 (50.0%) retainers had some type of failure with chemically cured and light-cured adhesive, respectively (log-rank test, P = 0.35). Data were analyzed on an intention-to-treat basis, and the hazard ratio (HR) was 1.15 (95% confidence interval [CI], 0.88-1.70; P = 0.47). There was weak evidence that age is a significant predictor for lingual retainer failures (HR, 0.96; 95% CI, 0.93-1.00; P = 0.08). Adhesive remnant index scoring was possible for only 66 of the 102 (64.7%) failures and did not differ between composites (Fisher exact test, P = 0.16). No serious harm was observed other than gingivitis associated with plaque accumulation.
  
  
  CONCLUSIONS
  The results of this study indicated no evidence that survival of mandibular lingual retainers differs between chemically and light-cured adhesives. The overall failure rate was 46.4%; however, this included any type of failure, which may have exaggerated the overall failure rate.
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Faculty of Medicine, University of Bern, Bern, Switzerland. npandis@yahoo.com
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Pandis
authors.forename: Padhraig S
authors.initials: PS
authors.lastname: Fleming
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Kloukos
authors.forename: Argy
authors.initials: A
authors.lastname: Polychronopoulou
authors.forename: Christos
authors.initials: C
authors.lastname: Katsaros
authors.forename: Theodore
authors.initials: T
authors.lastname: Eliades
mesh_terms: D000268:Adhesiveness; D000293:Adolescent; D000328:Adult; D002648:Child; D020770:Compomers / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental / Q000145:classification; D001840:Dental Bonding / Q000379:methods*; D004868:Equipment Failure; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018704:Orthodontic Retainers; D058105:Polymerization; D019279:Resin Cements / Q000737:chemistry* / Q000528:radiation effects; D055116:Self-Curing of Dental Resins / Q000379:methods*; D016019:Survival Analysis; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: C438705:Assure cement; D020770:Compomers; D003188:Composite Resins; D019279:Resin Cements; C087211:maximum cure