INTRODUCTION: 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.

Assistant professor Department of Orthodontics 1st Medical Faculty of Charles University Prague Czech Republic; postgraduate student Department of Orthodontics Clinic of Dental Medicine Palacky University Olomouc Czech Republic

Assistant professor Department of Orthodontics Clinic of Dental Medicine Palacky University Olomouc Czech Republic; consultant orthodontist Department of Orthodontics 1st Medical Faculty of Charles University Prague Czech Republic

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