The effect of conventional versus figure-of-eight module ligation on mandibular incisor alignment: a randomised controlled trial.

OBJECTIVE: To determine whether using figure-of-eight modules affects the rate of lower incisor alignment compared with conventionally tied modules.

DESIGN: Prospective randomised controlled trial.

SETTING: Orthodontic department at Queen's Hospital, Burton upon Trent, UK.

METHODS: One hundred and twenty participants were randomly allocated to conventional module or figure-of-eight module groups, stratified for extraction or non-extraction lower arch treatment. Eligibility criteria included patients who were 12-15 years of age at the start of treatment, in the permanent dentition, and had mandibular incisor irregularity of 5-10 mm (clinical observation). The primary outcome was the rate of lower incisor alignment during the first 12 weeks of orthodontic treatment. The secondary outcome was bracket failure rate. Lower labial segment alignment was measured on study models using the Little's Irregularity Index at the start (T0) of treatment, at 6 weeks (T1) and 12 weeks (T2). Case records were analysed to assess the number of bracket failures.

RESULTS: The four groups were well matched at baseline with respect to gender, age and irregularity. All patients completed the trial and data were analysed on an intention to treat basis. In both ligation groups, the lower teeth aligned significantly faster when the treatment involved extractions, for the time periods T0-T1 and T0-T2 (p < 0.05). There were no statistically significant differences between conventional module and figure-of-eight module ligation on the rate of alignment (per month) for all three-time periods. The bracket failure rate was also similar in both test groups; 4.08% for conventional and 3.21% for figure-of-eight ligation.

CONCLUSIONS: Ligation with figure-of-eight modules has no clinically significant effect on the rate of lower incisor alignment; it does not seem to hinder or quicken the alignment of teeth. There were no differences in the mean number of bracket failures per person.