A Randomised Clinical Trial of the Effectiveness of Orthodontic Treatment between the 0.018-inch and the 0.022-inch Slot Conventional Ligation Bracket Systems

  • Yassir A. Yassir Al-Naseri

Student thesis: Doctoral ThesisDoctor of Philosophy


Aim: To compare the effectiveness of orthodontic treatment with the 0.018-inch and 0.022-inch slot conventional MBT bracket systems. The primary objective was to compare duration of treatment and the secondary objectives were to compare (1) quality of treatment outcomes as measured by the American Board of Orthodontics Cast-Radiograph Evaluation (ABO CR-EVAL), Peer Assessment Rating (PAR) scores, incisor inclination, anchorage loss, and patient perception; and (2) biological side effects of treatment as evaluated by the amount of maxillary central incisor root resorption after nine months from the start of treatment.

Design: 2-arm parallel active group randomised clinical trial (RCT) with a 1:1 allocation ratio.

Setting: Secondary care hospital environment in the National Health Service (NHS) Tayside in Scotland, United Kingdom.

Subjects and Methods: Eligible patients aged 12 years or over were randomly allocated to treatment with either the 0.018-inch or 0.022-inch slot conventional MBT bracket systems (Victory series, 3M-Unitek, Monrovia, California). Randomisation was accomplished using a computer generated random code to a 10-number block of participants with allocation concealed in sequentially numbered, identical, opaque, and sealed envelopes. Outcome assessment was blinded. The treatment and archwire sequence were standardised and data were collected before, during and after treatment. Treatment outcome measures included: (1) duration of treatment (2) number of appointments and other treatment-related factors (3) ABO CR-EVAL (4) PAR scores and percentage PAR score reduction (5) incisor inclination, using cephalometric radiographs before and near end of treatment (6) anchorage loss (bilateral premolar extraction cases only), using 3D digital dental models with OrthoAnalyzer software (3Shape, Copenhagen, Denmark) (7) patient perception using the aesthetic component of the Index of Orthodontic Treatment Need (IOTN AC) and three validated questionnaires before, during and after treatment and (8) central incisor root resorption using periapical radiographs before treatment and after nine months of treatment. Parametric tests (independent samples t-test and two-way ANOVA) and non-parametric tests (Chi-square with Fisher’s exact tests, Mann-Whitney U test) were used to assess any differences between the groups. A multiple linear regression analysis was used to identify factors that influenced treatment duration for the total sample (P < 0.05).

Results: One hundred and eighty-seven participants were randomised to treatment groups. Of those 34 participants withdrew or were excluded due to protocol deviations and poor cooperation. There were 77 patients in the 0.018-inch slot bracket group and 76 patients in the 0.022-inch slot bracket group (105 females and 48 males, overall mean age: 19.05 years). The baseline characteristics were similar between groups (P > 0.05). For the 0.018-inch and 0.022-inch groups: mean duration of treatment 29.26 and 31.17 months; median number of appointments 16 and 17; mean total ABO CR-EVAL score 34.71 and 34.49; mean percentage PAR score reduction 74.07% and 77.13%; mean change for maxillary incisor inclination 2.9˚ and 1.5˚ and for mandibular incisor inclination 2.7˚ and 1.4˚; mean anchorage loss (Left) 3.30 mm and 3.47 mm (Right) 3.86 mm and 3.73 mm, respectively. Incisor root resorption after nine months of treatment and improvement in patient perception of aesthetics after treatment were statistically significant with both groups (P < 0.05). However, there were no statistically significant differences between the two treatment groups in terms of treatment duration, number of appointments, ABO CR-EVAL, percentage PAR score reduction, incisor inclination, anchorage loss, patient perception of treatment, and incisor root resorption (P > 0.05). The regression analysis revealed that 33% of the variance in treatment duration could be explained by five variables: age at bonding, Class II division 2 malocclusion, number of failed appointments, number of emergency appointments, and greater than one clinician. No adverse events were observed during treatment.

Conclusions: There were no statistically or clinically significant differences in the duration of treatment, quality of occlusal outcomes, incisor torque delivery, patient perception or root resorption with either the 0.018-inch or 0.022-inch slot conventional MBT appliances. Increasing patient age, Class II division 2 malocclusion, number of failed and emergency appointments, and multi-operator treatment all increase the duration of orthodontic treatment.
Date of Award2017
Original languageEnglish
SupervisorDavid Bearn (Supervisor) & Grant McIntyre (Supervisor)

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