(Am J Orthod Dentofacial Orthop 2016;149:202-11)

Unexpected complications associated with mandibular fixed retainers: A retrospective study

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 6 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 6 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 5 0.03) and had higher mandibular plane angles (P\0.0001) and increased pretreatment ventral positions of the mandibular incisors (P 5 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. (Am J Orthod Dentofacial Orthop 2016;149:202-11)

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