Self-ligating vs Conventional Brackets and Labial Bone Thickness During Crowding Correction in Adults

Dental crowding is one of the most common malocclusions. Non-extraction treatment is increasingly popular, but moving teeth beyond the alveolar housing can lead to bone dehiscence, fenestration, and gingival recession, especially in the lower incisor region. Self-ligating bracket systems are claimed to produce a "Frankel-like effect", in which low-friction brackets and light-force Cu-NiTi wires allow the arch to reshape physiologically with the alveolar bone following the teeth. Clinical evidence for this claim is limited and conflicting.

Design: Two-arm, parallel-group randomized clinical trial with a 1:1 allocation ratio, reported according to CONSORT guidelines, conducted at the Orthodontic Department clinic, Faculty of Oral and Dental Medicine, Future University in Egypt.

Null hypothesis: There is no difference in the change in lower labial alveolar bone thickness between self-ligating and conventional brackets.

Randomization: A computer-generated random sequence (Microsoft Excel RAND function) will be produced by the study supervisor. Allocation will be concealed in sealed, opaque, folded envelopes kept in a box at the secretary's office. Patients will draw an envelope before bonding.

Blinding: Operator and participants cannot be blinded. Outcome assessors will be blinded; patient identifiers will be removed from radiographs and models, and two assessors will measure independently.

Interventions:

Conventional group: 0.022-inch slot Roth prescription stainless steel brackets (American Orthodontics) with elastomeric ligatures. Wire sequence: 0.012 and/or 0.014-inch NiTi (chosen according to crowding), 0.016-inch NiTi, 0.016 x 0.022-inch NiTi, then 0.017 x 0.025-inch stainless steel for 4 weeks.

Self-ligating group: Roth prescription self-ligating brackets (American Orthodontics). Wire sequence: 0.014-inch Cu-NiTi for at least 10 weeks, 0.014 x 0.025-inch Cu-NiTi for at least 10 weeks, then 0.017 x 0.025-inch stainless steel customized to arch form for 4 weeks.

Patients will be reviewed monthly, with an intraoral scan at each visit. CBCT, standardized photographs, intraoral scans, and periodontal evaluation will be taken at baseline (T0) and at the end of leveling and alignment (T1).

Sample size: Using G*Power 3.1.9.7 with alpha 0.05, power 80%, and effect size d = 1.51 from a previous study, 16 participants are needed (8 per group), increased by 20% for dropout to 20 (10 per group).

Statistical analysis: Normality will be checked with Kolmogorov-Smirnov and Shapiro-Wilk tests. Normally distributed data will be compared with independent t-tests, and non-normal data with the Mann-Whitney U test. Categorical data will be analyzed with chi-square tests. Significance is set at p ≤ 0.05 (IBM SPSS Statistics v26). Intra- and inter-examiner reliability will be assessed with the intraclass correlation coefficient and kappa.