Determining the midsagittal reference plane for evaluating facial asymmetries

I read with great interest the article in the August issue of the AJO-DO entitled “Statistical shape analysis-based determination of optimal midsagittal reference plane for evaluation of facial asymmetry.” The authors aimed to determine an optimal landmark-based midsagittal reference plane for evaluation of facial asymmetry, comparing this plane with an individual symmetric midsagittal reference plane calculated by superimposing the original and mirrored configuration using Procrustes fits. They suggested 3 landmarks (nasion, anterior nasal spine, and posterior nasal spine) for determination of the midsagittal reference plane in patients with mild-to-moderate facial asymmetry.

I would like to congratulate the authors for this article, since it is fundamental to determine an accurate midsagittal plane to evaluate asymmetries. The suggested plane is established with landmarks that are easy to determinate and have great repeatability and reproducibility. However, some points should be mentioned.

First, by assuming the proposed landmark-based midsagittal reference plane, the evaluation of transversal maxillary asymmetries is quite difficult, since it presupposes that some landmarks in the maxilla are always stable. This is even more preoccupying for points located near the anterior nasal spine (suggested as a stable reference). How did the authors analyze this limitation? Shouldn’t other landmarks in the cranial base (usually assumed to be a stable structure) be taken as references? I agree that there are some controversies on this topic, but the skull base has been used traditionally in our specialty.

Actually, a study published by Damstra et al that was cited some times in your article must be mentioned here. The authors compared a validated morphometric midsagittal plane with 6 different midsagittal planes described in the literature to evaluate asymmetries and confirmed that a midsagittal plane constructed through 2 midline structures (landmarks in the skull base) and perpendicular to the Frankfort horizontal plane was the most accurate. Therefore, don’t you think their method may the best to determine the midsagittal reference plane?

Once again, thank you for presenting this interesting study.

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Apr 4, 2017 | Posted by in Orthodontics | Comments Off on Determining the midsagittal reference plane for evaluating facial asymmetries
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