title: Unexpected complications associated with mandibular fixed retainers: A retrospective study.
abstract: BACKGROUND
  The purposes of this retrospective study were to describe the types of unexpected complications associated with mandibular fixed retainers and to assess their prevalences and possible etiologic causes.
  
  
  METHODS
  A total of 3500 consecutive patients (1423 male, 2077 female) treated with fixed appliances and a mandibular fixed retainer as a part of the retention protocol were screened during the retention period (2008-2013) for unexpected complications. Thirty-eight subjects (12 male, 26 female; mean age, 20.7 ± 8.9 years) with unexpected complications were identified and assigned to the unexpected complications group and compared with a randomly selected control group of 105 subjects (43 men, 62 women; mean age, 29.5 ± 9.7 years) without unexpected complications. Relationships between unexpected complications and cephalometric and clinical variables were evaluated.
  
  
  RESULTS
  An opposite inclination of the contralateral canines (twist effect) was found in 21 subjects. In 89.5%, the left canines were tipped buccally. A torque difference of 2 adjacent incisors (X effect) was identified in 12 patients. In 5 subjects, nonspecific complications were noted. Subjects in the unexpected complications group were significantly younger at debonding (P = 0.03) and had higher mandibular plane angles (P <0.0001) and increased pretreatment ventral positions of the mandibular incisors (P = 0.029). No differences were found between the groups with regard to treatment duration, wire type, failure rate, treatment changes in incisor proclination, or intercanine distance.
  
  
  CONCLUSIONS
  Unexpected complications of mandibular fixed retainers are relatively rare. Facial divergence was identified as a possible predictor. However, the etiology is most likely multifactorial. Strong asymmetry among the patients with the twist effect suggests that the mechanical properties of retention wires may play a role and should be examined in the future.
authors.affiliation: Assistant professor, Department of Orthodontics, First Medical Faculty of Charles University, Prague, Czech Republic; postgraduate student, Department of Orthodontics, Clinic of Dental Medicine, Palacky University, Olomouc, Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Kučera
authors.affiliation: Assistant professor, Department of Orthodontics, Clinic of Dental Medicine, Palacky University, Olomouc, Czech Republic; consultant orthodontist, Department of Orthodontics, First Medical Faculty of Charles University, Prague, Czech Republic. Electronic address: ortho.marek@email.cz.
authors.forename: Ivo
authors.initials: I
authors.lastname: Marek
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002508:Cephalometry / Q000379:methods; D002648:Child; D003481:Cuspid / Q000473:pathology; D003738:Dental Cements / Q000737:chemistry; D003766:Dental Occlusion; D005260:Female; D006801:Humans; D007180:Incisor / Q000473:pathology; D008297:Male; D008310:Malocclusion / Q000209:etiology; D008334:Mandible / Q000473:pathology; D016382:Orthodontic Appliance Design / Q000009:adverse effects; D018704:Orthodontic Retainers / Q000009:adverse effects*; D009969:Orthodontic Wires / Q000009:adverse effects; D019279:Resin Cements / Q000737:chemistry; D012189:Retrospective Studies; D012307:Risk Factors; D012399:Rotation; D019415:Torque; D055815:Young Adult
chemical_list: D003738:Dental Cements; D019279:Resin Cements; C586977:transbond supreme low viscosity