Removable thermoplastic appliances as orthodontic retainers--a prospective study of different wear regimens.

The aim of this prospective study was to evaluate and compare stability after 6 months of Essix retainer use. Patients' perceptions of wearing the retainer were also evaluated. A total of 69 patients, 53 girls and 16 boys [mean age 15.7 years, standard deviation (SD) 1.96], were included in the study and randomized into two groups with different wear regimens; full-time wear for 3 months and thereafter at night (group A) compared to full-time wear for 1 week and thereafter at night only (group B). Sixty patients completed the study and thus, group A comprised 30 maxillary retainers and 18 mandibular retainers and group B 30 maxillary and 18 mandibular retainers. Little's irregularity index (LII), overjet, and overbite were measured at debond (T(1)) and after 6 months (T(2)). Differences within and between groups were analysed with a Mann-Whitney test. At T(2), all patients completed a questionnaire in order to evaluate their experience of wearing an Essix retainer and how they complied with the given instructions. Differences in LII during T(1)-T(2) were 0.44 and 0.49 mm for group A and B, respectively, but with no significant difference between the groups. There were also no significant changes in overjet and overbite within or between the groups during T(1)-T(2). According to the responses to the questionnaire, the retainer was well tolerated by the patients. It was therefore concluded that the Essix retainer is sufficient for maintaining the results after orthodontic treatment and that night-time wear is adequate.