This randomized controlled clinical trial compares the effects of three orthodontic archwire protocols used during the alignment phase on anterior tooth roots and the supporting alveolar bone. Participants were randomly allocated to one of three parallel groups according to the experimental archwire used. Cone-beam computed tomography (CBCT) images were obtained before treatment initiation and after completion of the follow-up period. The primary outcome is volumetric root resorption, while secondary outcomes include changes in Buccal alveolar bone height and thickness. Recruitment and follow-up have been completed, and the study is currently in the data verification and statistical analysis phase. The findings are expected to help clinicians choose archwire protocols that reduce undesirable biological side effects during orthodontic treatment.

Orthodontic tooth movement may result in undesirable biological side effects, including external root resorption and remodeling of the alveolar bone surrounding the moved teeth. These effects are clinically important because they may influence long-term tooth support and treatment safety. During the alignment phase of orthodontic treatment, different archwire designs may produce different biomechanical effects; however, evidence comparing their influence on root structure and alveolar bone remains limited.

This study is a randomized controlled clinical trial designed to compare three orthodontic archwire protocols during the alignment phase in patients undergoing fixed orthodontic treatment. The primary objective is to assess volumetric root resorption in the anterior teeth using three-dimensional CBCT-based measurements. Secondary objectives include assessment of alveolar bone height change, and alveolar bone thickness change at standardized cervical, middle, and apical levels.

Participants were enrolled from the Department of Orthodontics, Faculty of Dentistry, Damascus University. Eligible patients were randomly allocated to one of three parallel groups. All groups received the same initial alignment sequence using 0.014-inch nickel-titanium and 0.016-inch nickel-titanium archwires. The groups differed in the experimental archwire used thereafter. The square group received a 0.016 × 0.016-inch nickel-titanium archwire, the rectangular group received a 0.016 × 0.022-inch nickel-titanium archwire, and the control group continued with a 0.016-inch round nickel-titanium archwire. Archwire changes were performed at standardized 35-day intervals according to the study protocol.

CBCT records were obtained at baseline before treatment initiation and again at the end of the observation period. Root volume measurements were used to calculate volumetric root resorption in cubic millimeters and as a percentage of the baseline root volume. Buccal alveolar bone height and thickness were measured on standardized CBCT sections using predefined reference planes and anatomical landmarks.

Participant recruitment started on 01 October 2023, and follow-up of the last participant was completed on 25 June 2025. The study is currently in the data verification and statistical analysis phase.

Inclusion Criteria:

• Patients aged between 16 and 25 years
• Presence of a complete permanent dentition
• Moderate crowding ranging from 4 to 6 mm, according to Little's Irregularity Index (Little, 1975)
• Indication for non-extraction orthodontic treatment
• Normal or slightly retroclined incisors, as evaluated radiographically and on study models
• Good oral health status
• Periodontally healthy supporting tissues

Exclusion Criteria:

• Patients with severe skeletal discrepancies
• Patients with craniofacial anomalies
• Presence of impacted or supernumerary teeth
• History of previous orthodontic treatment
• Presence of systemic conditions or use of medications known to influence tooth movement
• Pregnant women
• Patients for whom the follow-up (T1) records were not obtained within the permitted 35-day window