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Comparison of two methods for quantitative assessment of mandibular asymmetry using cone beam computed tomography image volumes.

OBJECTIVES
The aim of this study was to compare two methods of measuring mandibular asymmetry. The first method uses mirroring of the mandible in the midsagittal plane; the second uses mirroring of the mandible and registration on the cranial base.


METHODS
Surface models were constructed from cone beam CT (CBCT) scans of 50 patients with asymmetry. For the first approach, a midsagittal plane was defined for each patient as the plane passing through nasion, anterior nasal spine and basion. Mirrors for both halves of the mandible were created. The second approach consisted of mirroring the image volume by flipping the left and right sides and then registering the mirrored image onto the cranial base using a mutual information maximization method. Surface distances between hemimandibles and mirrors were calculated for nine regions.


RESULTS
There was no statistically significant difference between the mean surface distance measurements obtained with the two approaches and when comparing both halves in most areas.


CONCLUSION
Both mirroring techniques provided similar quantification of mandibular asymmetry in this cohort.