This randomized controlled clinical trial will compare external apical root resorption in patients undergoing maxillary canine retraction using modified corticotomy-assisted frictionless T-loop mechanics versus conventional frictionless T-loop mechanics. Sixty orthodontic patients requiring extraction of maxillary first premolars will be randomly assigned to two groups. Changes in canine root length will be measured on panoramic radiographs taken before and after retraction to determine the extent of external apical root resorption. The study will evaluate whether modified corticotomy-assisted retraction results in different root resorption outcomes compared to conventional retraction.

External apical root resorption is a known complication of orthodontic treatment and may be influenced by the magnitude and duration of orthodontic force. Methods that accelerate tooth movement may reduce overall treatment time and potentially influence the extent of root resorption.

Corticotomy-assisted orthodontics is based on the regional acceleratory phenomenon, which enhances bone remodeling and facilitates tooth movement. Modified corticotomy techniques involve limited surgical injury to the cortical bone to stimulate accelerated movement while minimizing postoperative morbidity. Frictionless mechanics using T-loops allow controlled canine retraction with reduced frictional resistance between the bracket and archwire.

This single-center randomized controlled clinical trial will enroll 60 patients aged 12 to 30 years who require bilateral extraction of maxillary first premolars as part of orthodontic treatment. Participants will be randomly allocated in a 1:1 ratio to:

Group A: Modified corticotomy-assisted canine retraction with frictionless T-loop mechanics Group B: Conventional frictionless T-loop canine retraction

All participants will be treated using 0.022 × 0.028-inch preadjusted edgewise appliances. Standardized T-loop activation delivering controlled force will be performed at three-week intervals until canine retraction is completed.

External apical root resorption will be assessed by measuring linear changes in root length from the canine cusp tip to the root apex on calibrated pre- and post-retraction panoramic radiographs using digital measurement software. The primary outcome measure will be the mean change in root length between baseline and post-retraction assessments. Statistical analysis will compare the magnitude of root resorption between the two groups.

Inclusion Criteria:

• Patients aged 12-30 years requiring canine retraction into maxillary first premolar extraction spaces
• Patients with normal vertical skeletal pattern (mandibular plane angle 32° ± 5°)
• Patients with healthy periodontium

Exclusion Criteria:

• Syndromic patients
• Patients with systemic conditions requiring long-term medication affecting orthodontic tooth movement (e.g., NSAIDs, bisphosphonates, anticonvulsants)
• Mixed dentition cases
• Patients with pre-existing root resorption
• Patients who fail to attend scheduled appointments

IPD will not be shared to maintain participant confidentiality and due to institutional data protection policies.

The investigator responsible for measuring root length and width on calibrated OPG radiographs using ViewBox software will be blinded to group allocation. Radiographs will be coded to prevent identification of the intervention group.