External Apical Root Resorption in Three Miniscrew-Supported Maxillary En-Masse Retraction Mechanics: A Randomized Controlled Trial

Orthodontic camouflage treatment of adult patients with Class II Division 1 malocclusion frequently involves extraction of the maxillary first premolars followed by retraction of the upper anterior teeth. Temporary orthodontic miniscrews can provide skeletal anchorage during this stage and allow the six maxillary anterior teeth to be retracted together as one unit. Although these mechanics are widely used, the anterior teeth remain exposed to orthodontic forces during both the initial leveling and alignment phase and the subsequent retraction phase. External apical root resorption is therefore an important biological safety outcome that should be evaluated throughout treatment rather than only after space closure has been completed.

This single-center, three-arm, parallel-group randomized clinical trial was conducted at the Department of Orthodontics, Faculty of Dentistry, Damascus University. Sixty adult patients with Class II Division 1 malocclusion who required extraction-based orthodontic camouflage treatment were allocated equally to one of three treatment groups: a bidimensional bracket group, a hybrid dual-section archwire group, or a conventional sliding mechanics group.

The three approaches differed in the relationship between the anterior brackets and the working archwire. The bidimensional approach used smaller anterior bracket slots with larger posterior slots. The hybrid dual-section approach used a customized archwire with different anterior and posterior cross-sections, while the conventional group used a continuous archwire with a uniform cross-section. These mechanical differences may influence archwire engagement, force expression, and the distribution of forces applied to the roots of the maxillary anterior teeth. Their possible effect on external apical root resorption therefore required direct clinical comparison.

All participants underwent bilateral extraction of the maxillary first premolars, fixed-appliance leveling and alignment, and miniscrew-supported en-masse retraction of the six maxillary anterior teeth. The same general treatment stages and skeletal anchorage concept were used in all groups, while the bracket-slot and archwire configurations varied according to group allocation. Retraction continued until an acceptable overjet and a Class I canine relationship were achieved. Participants were reviewed regularly throughout treatment, and miniscrew-related or other treatment-associated adverse events were recorded.

Digital panoramic radiographs were obtained before orthodontic treatment, at the end of leveling and alignment immediately before retraction, and after completion of en-masse retraction. The maxillary central incisors, lateral incisors, and canines on both sides were assessed individually. Crown length was used as a stable reference to correct for differences in radiographic magnification between time points.