Bracket Positioning Techniques and Quality of Orthodontic Finishing

Comparison of Three Bracket Positioning Techniques (Smile Arc Protection, Smile Arc and Marginal Ridge Approach, and McLaughlin-Bennett-Trevisi) on the Quality of Orthodontic Finishing, Mini-Esthetics, and Anterior Tooth Tip and Torque: A Three-Arm Randomized Clinical Trial

This three-arm randomized clinical trial compares three orthodontic bracket positioning techniques - Smile Arc Protection (SAP), Smile Arc and Marginal Ridge Approach (SAMRA), and the McLaughlin-Bennett-Trevisi (MBT) bracket placement chart (control) - in young patients with Angle Class I malocclusion and mild-to-moderate crowding treated non-extraction. The primary aim is to determine which technique yields the highest quality of orthodontic finishing, measured with the American Board of Orthodontics Objective Grading System (ABO-OGS). Secondary aims compare anterior tooth tip and torque (assessed by CBCT) and mini-esthetic smile parameters (gingival display, incisal display, buccal corridor, and smile arc, assessed on standardized posed-smile photographs) among the three techniques.

Bracket positioning is one of the most influential operator-dependent factors affecting the quality of orthodontic finishing and the resulting smile esthetics. Three contemporary positioning philosophies are compared in this trial.

Design. Eligible participants are randomly allocated 1:1:1 to one of three parallel arms. Allocation is generated with an online randomizer, concealed in sequentially opaque sealed envelopes held by a co-supervisor, and revealed only on the day of intervention. Outcome assessors are blinded; operator blinding is not feasible.

Intervention. All arms receive a fully digital indirect-bonding workflow (intraoral scanning, virtual bracket placement in 3Shape Ortho-Analyzer, 3D-printed casts, vacuum-formed transfer trays) using a 0.018-inch MBT prescription, and an identical arch wire sequence ending in a 0.017 in × 0.025 in stainless steel wire maintained for three months. The arms differ only in the vertical/angular bracket-positioning rule applied (SAP, SAMRA, or MBT chart).

Assessment. Records are captured before bonding (T₀) and at the end of levelling and alignment (T₁). The ABO-OGS is scored on 3D-printed casts and the panoramic radiograph; tip and torque are measured on dentoalveolar CBCT; mini-esthetic parameters are measured on standardized frontal posed-smile photographs calibrated in Adobe Photoshop.

Inclusion Criteria:

1. Males and females aged 14-25 years with a full permanent dentition.
2. Mild to moderate crowding requiring non-extraction orthodontic treatment (2-6 mm per Graber's classification).
3. Angle Class I malocclusion.
4. Normal skeletal vertical dimension (SN-MP angle 32° ± 5°).

Exclusion Criteria:

• 1. Medication that may cause gingival inflammation (e.g., cyclosporine, phenytoin).

  2. Impacted, extracted, or missing permanent teeth (except third molars). 3. Periodontal disease or parafunctional habits (bruxism, tongue thrusting, mouth breathing).

  4. History of previous orthodontic treatment. 5. Craniofacial anomalies, facial asymmetry, or skeletal discrepancy.