Effect of time between archwire changes on intended dentoalveolar expansion in orthodontic patients treated with fixed appliances : Aprospective controlled clinical trial.

Abstract

To analyze the effects of the time span between archwire changes on the amount of transverse dental arch expansion. The design was aprospective, controlled clinical trial. Randomization was performed by computer-generated allocation tables. In all, 35patients were evaluated in three groups treated with fixed appliances and the same four sequential leveling archwires, however, with different replacement periods: 28days (4-week [4W] group), 56days (8-week [8W] group), and 84days (12-week [12W] group). Digital models were measured before the treatment (T0) and at the end of the evaluation period (T1) by ablinded operator with OrthoAnalyzer® software (3-Shape, Copenhagen, Denmark) and compared using MANOVA. Amultiple linear regression was also used to evaluate the influences of age, initial dental crowding, incisor inclination, and facial pattern on the amount of expansion. Mean expansion was 2.77 ± 0.84 mm (upper arch) and 3.12 ± 0.88 mm (lower arch) in the 12Wgroup; 1.96 ± 0.82 mm and 2.27 ± 0.96 mm in the 8Wgroup, and 1.11 ± 0.93 mm and 1.32 ± 0.91 mm in the 4Wgroup, respectively for the upper and lower arches. The amount of expansion varied significantly between the groups in the area of the canines, first premolars, and second premolars for both arches. Expansion was less in older patients. Initial dental crowding, incisor inclination and facial pattern had no influence on dental expansion. Longer time spans between archwire changes provided greater amounts of expansion, while age is inversely related, with younger patients expressing greater amounts of expansion. The results also suggest that the expansion provided by the fixed appliances is expressed mainly in the canine and premolar areas.