CBCT Image Superimposition for Longitudinal Monitoring of Mandibular Cyst Healing: A Technical Note

To evaluate the effectiveness of spatial superimposition of cone-beam computed tomography (CBCT) scans acquired at baseline and 6-month follow-up for monitoring bone healing in mandibular cystic lesions, aiming to reduce variability in conventional volumetric comparisons and enhance accuracy, reproducibility, and spatial fidelity of radiographic assessments.

Two CBCT scans of a single patient (baseline, T0; follow-up, T1) were imported into 3D Slicer v5.8.0. The mandible was isolated by manually cropping a region of interest, and the cystic lesion was segmented semi-automatically using the Grow from Seeds tool. A rigid six-degree-of-freedom registration aligned T1 to T0; the resulting transformation matrix was applied to the T1 segmentation to enable direct voxel-wise comparison. Lesion volumes were measured, and spatial subtraction analysis quantified the resorbed area.

Lesion volume decreased from 1841.64 mm³ at T0 to 1362.62 mm³ at T1, corresponding to an absolute reduction of 479.02 mm³ (26.0%). The subtraction mask accurately localized regressed voxels, confirming both the magnitude and spatial distribution of bone healing.

Potential limitations related to CBCT artifacts and the need for operator-dependent manual steps should be considered when interpreting the results. Overall, CBCT superimposition with semi-automatic segmentation provides an objective, consistent, and anatomically precise approach for monitoring mandibular cyst regression and may represent a useful tool to support conservative management strategies.