Abstract
Purpose
Reconstruction of the facial midplane is relevant in anthropometry, orthodontics, maxillofacial surgery, and the accurate measurement of symmetry deviation is relevant in many fields of medicine especially when planning surgical treatment. In the literature, three different means of midplane generation have been published; however, there is currently no consensus regarding the approach to use. Morphometric methods are used to determine the true midsagittal plane (MSP), but its use in clinical practice is difficult. A regression plane based on N‑ANS-PNS landmarks reportedly approximates the morphometric MSP. As these points are vulnerable, we investigated which combination of landmarks can be substituted in symmetric and asymmetric faces.
Patients and methods
Thirty symmetric and 30 asymmetric faces were analyzed on cone-beam computed tomography scans. A total of 50 regression planes were generated based on three unpaired landmarks and 35 regression planes were generated based the midpoints of paired landmarks. The Na-ANS-PNS plane was used as reference plane, and the mean angle between it and each generated MSP was calculated. The differences from the reference plane were compared by t‑test between the groups.
Results
In the symmetric group, 86% of angles deviated by <5° using unpaired points, whereby 74% of angles deviated by <5° for paired points. Between the two groups 50% of planes from midline points, and 77% of planes from paired points were significantly different. All planes deviated more in the asymmetric group.
Conclusions
The N‑ANS-PNS reference plane can be substituted with the following combinations: ANS-G-Ba, ANS-G-S, ANS-S-De, PNS-G-Ba, PNS-S-Ba, PNS-ANS-G, and PNS-N-Ba.
Zusammenfassung
Ziel
Die Rekonstruktion der Gesichtsmittelebene ist von Bedeutung in der Anthropometrie, der Kieferorthopädie sowie der Mund‑, Kiefer- und Gesichtschirurgie. In vielen Bereichen der Medizin ist die genaue Bestimmung einer Symmetrieabweichung relevant, insbesondere bei der Planung chirurgischer Interventionen. In der Literatur wurden drei Verfahren zur Bestimmung der Midsagittalebene veröffentlicht, es gibt jedoch keinen Konsens über die Vorgehensweise. Zur Bestimmung der tatsächlichen mittsagittalen Ebene („true midsagittal plane“, MSP) werden morphometrische Methoden eingesetzt, die sich jedoch in der Klinik schwer umsetzen lassen. Berichtet wird, dass sich eine auf N‑ANS-PNS basierende Regressionsebene der morphometrischen MSP nähert. Wegen der Vulnerabilität dieser Punkte wurde untersucht, welche Kombination von Referenzpunkten sich bei symmetrischen bzw. asymmetrischen Gesichtern ersatzweise eignet.
Patienten und Methoden
Es wurden insgesamt 60DVTs ausgewertet: 30 von symmetrischen und 30 von asymmetrische Gesichtern. Basierend auf drei unpaarigen Referenzpunkten wurden insgesamt 50 Regressionsebenen generiert, 35 Regressionsebenen basierten auf den gemittelten paarigen Referenzpunkten. Als Bezugsebene wurde die Na-ANS-PNS-Ebene verwendet und der mittlere Winkel zwischen dieser und jedem erzeugten MSP wurde berechnet. Die Unterschiede zur Bezugsebene zwischen den Gruppen wurden mittels t‑Test evaluiert.
Ergebnisse
In der symmetrischen Gruppe wichen 86 % der Winkel um <5° bei unpaarigen Punkten ab, 74 % der Winkel wichen bei paarigen Punkten um <5° ab. Zwischen beiden Gruppen waren 50 % der Ebenen von Mittellinienpunkten und 77 % der Ebenen von gepaarten Punkten signifikant unterschiedlich. Alle Ebenen wichen in der asymmetrischen stärker als in der symmetrischen Gruppe ab.
Schlussfolgerungen
Die N‑ANS-PNS-Referenzebene kann durch folgende Kombinationen ersetzt werden: ANS-G-Ba, ANS-G-S, ANS-S-De, PNS-G-Ba, PNS-S-Ba, PNS-ANS-G und PNS-N-Ba.
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Acknowledgements
We would like to thank Editage (www.editage.com) for English language editing. This study was supported by the ÚNKP-17-3 New National Excellence Program of the Ministry of Human Capacities of Hungary.
Funding
This study was supported by the ÚNKP-17-3 New National Excellence Program of the Ministry of Human Capacities of Hungary.
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A. Dobai, Z. Markella, T. Vízkelety, C. Fouquet, A. Rosta and J. Barabás declare that they have no competing interests.
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Dobai, A., Markella, Z., Vízkelety, T. et al. Landmark-based midsagittal plane analysis in patients with facial symmetry and asymmetry based on CBCT analysis tomography. J Orofac Orthop 79, 371–379 (2018). https://doi.org/10.1007/s00056-018-0151-3
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DOI: https://doi.org/10.1007/s00056-018-0151-3