# Three-dimensional CBCT analysis of bone remodeling, root resorption, and incisive canal morphology during miniscrew-assisted aligner-based incisor retraction with and without extractions

## TL;DR

This study used 3D imaging to compare how bone and tooth changes differ when moving upper teeth with or without extractions using clear aligners.

## Contribution

The study provides new empirical evidence on bone remodeling and root resorption differences between extraction and non-extraction orthodontic treatments.

## Key findings

- Extraction-based retraction caused greater reductions in canal width, cortical bone width, and root–canal distance compared to non-extraction.
- Apical root resorption was significantly higher in the extraction group, correlating with closer root–canal proximity.
- Treatment duration, incisor movement, and root length were significant predictors of root resorption and canal contact.

## Abstract

This study aimed to investigate three-dimensional changes in incisive canal (IC) morphology, root–canal proximity, and root resorption following maxillary incisor (U1) retraction with clear aligners, comparing extraction and non-extraction treatment protocols.

A total of 100 patients (200 U1) treated with clear aligners were retrospectively analyzed using CBCT before and after treatment. The extraction group included 40 patients and the non-extraction group 60. Linear measurements of IC width, root–canal distance, cortical bone width (CBW), IC height, and root length/width were obtained at three levels above the labial cementoenamel junction (H1–H3: 2, 4, and 6 mm). Volumetric and surface area analyses of the IC and U1 were performed to evaluate morphological and structural remodeling. Group differences and predictive factors for root resorption and canal contact/invasion were assessed statistically.

Extraction-based retraction produced significantly greater reductions in canal width, CBW, and root–canal distance, with increased apical root resorption, most notably in patients who underwent substantial anterior retraction (all P < 0.05). The mean decreases in root–canal distance were 1.08 ± 0.92 mm, 1.10 ± 0.91 mm, and 1.02 ± 0.99 mm at H1, H2, and H3, respectively, in extraction cases, vs. 0.40 ± 0.58 mm, 0.47 ± 0.78 mm, and 0.30 ± 0.98 mm in non-extraction cases. Apical root resorption averaged 0.91 ± 0.80 mm in the extraction group and 0.32 ± 0.56 mm in the non-extraction group (P < 0.05), correlating with closer root–canal proximity. Volumetric and surface area analyses revealed greater reductions in IC and U1 dimensions in extraction cases, indicating intensified bone remodeling. Treatment duration, incisor movement, IC height, and root–canal distance were significant predictors of canal contact, while root resorption correlated positively with treatment duration, incisor movement, and root length.

Extraction-based aligner retraction elicits greater osseous remodeling around the incisive canal and increased root resorption, particularly in cases requiring substantial anterior retraction, reflecting a coupled bone–tooth adaptive response to orthodontic loading. These findings highlight the dynamic nature of craniofacial bone physiology and emphasize the need for biologically guided treatment planning to minimize tissue stress and iatrogenic effects.