Survival of flexible, braided, bonded stainless steel lingual retainers: a historic cohort study

The objectives of this study were to retrospectively evaluate the clinical survival rate of flexible, braided, rectangular bonded stainless steel lingual retainers, and to investigate the influence of gender, age of the patient, and operator experience on survival after orthodontic treatment at the Department of Orthodontics, University of Groningen, between the years 2002 and 2006. The study group comprised of 277 patients [162 females: median age 14.8 years, interquartile range (IQR) 13.6-16.5 years and 115 males: median age 15.3 years, IQR 14.2-16.7 years]. After acid etching the lingual surfaces of each tooth, an adhesive resin was applied and retainers were bonded using a flowable resin composite. Data concerning, failures, gender, age of the patient, and operator experience were retrieved from the patient files that were updated by chart entries every 6 months or when failure was reported by the patient. The maximum follow-up period was 41.7 months. All 277 patients received flexible, braided, bonded mandibular canine-to-canine retainers. Eighteen failures were observed in the maxilla. A failure was recorded when there was debonding, fracture, or both, occurring in one arch. Only first failures were used for statistical analysis. When failures occurred in both jaws, these were considered as two separate incidences. Ninety-nine debonding (35.7 per cent), two fractures (0.7 per cent), and four debonding and fracture (1.4 per cent) events were observed. No significant effect (P > 0.05) of gender (females: 41 per cent, males: 32 per cent) or patient age (<16 years: 37 per cent, > or =16 years 38.7 per cent) was observed. The failure rate did not differ due to operator experience (n = 15; less experienced: 38.0 per cent; moderately experienced: 28.9 per cent, professional: 46.7 per cent; P > 0.05; chi-square test). Kaplan-Meier survival curves showed a 63 per cent success rate for the bonded lingual retainers over a 41.7 month period.