A randomized clinical trial of the effectiveness of 0.018-inch and 0.022-inch slot orthodontic bracket systems: part 1-duration of treatment.

Objective: To compare treatment duration between 0.018-inch and 0.022-inch slot systems and determine factors influencing treatment duration.
Subjects and Methods: Eligible participants aged 12 years or over were allocated to the 0.018-inch or 0.022-inch slot MBT appliance (3M-Unitek, Monrovia, California, USA) using block randomization in groups of 10. Outcome measures included duration of: 1. overall treatment, 2. levelling and alignment, 3. working and finishing, and 4. appointment numbers and other treatment-related factors. Parametric tests (independent samples t-test) and non-parametric tests (chi-square with Fisher's exact tests and Mann-Whitney U-test) assessed differences between groups. A multiple linear regression analysis identified factors influencing treatment duration (P < 0.05).
Results: Of the 187 participants randomized (1:1 ratio), 34 withdrew or were excluded (protocol deviations or poor cooperation). There were 77 patients in the 0.018-inch slot group and 76 patients in the 0.022-inch slot group (overall mean age: 19.1 years). Baseline characteristics were similar between groups (P > 0.05). The mean duration of treatment for the 0.018-inch and 0.022-inch slot groups was 29.3 and 31.2 months, respectively. There were no statistically significant differences between the two treatment groups in terms of treatment duration, duration of the key stages of treatment, and number of appointments (P > 0.05). The regression analysis revealed 33.0 per cent of variance in treatment duration was explained by age at bonding, Class II division 2 malocclusion, number of failed appointments, number of emergency appointments, and transfer to another clinician. There were no adverse events.
Limitations: It was impossible to blind clinicians or patients to allocation and oral hygiene and periodontal outcomes were not assessed.
Conclusions: There was no statistically or clinically significant difference in treatment duration between 0.018-inch and 0.022-inch slot bracket systems. Increasing patient age, Class II division 2 malocclusion, number of failed and emergency appointments, and multi-operator treatment all increase orthodontic treatment duration.
Registration: The trial was registered with ClinicalTrials.gov on 5 March 2014, registration number: NCT02080338.
Protocol: The protocol was published at DOI: 10.1186/1745-6215-15-389.
(© The Author(s) 2018. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.)