Korean J Orthod.  2023 Jul;53(4):219-231. 10.4041/kjod23.015.

Differences in positions of cone-beam computed tomography landmarks in patients with skeletal Class III facial asymmetry according to midsagittal planes

• Noh HK
• Kim HJ
• Park HS

• KMID: 2545038
• DOI: http://doi.org/10.4041/kjod23.015

Abstract

Objective
This study aimed to clarify differences in the positions of cone-beam computed tomography (CBCT) landmarks according to different midsagittal planes (MSPs) in patients with skeletal Class III facial asymmetry.
Methods
Pre-treatment CBCT data from 60 patients with skeletal Class III were used. The patients were classified into symmetric (menton deviations of < 2 mm) or asymmetric (menton deviations of > 4 mm) groups. Six MSPs were established based on previous studies, and three-dimensional analyses were performed for the planes in both the groups. The measurement outcomes were compared statistically.
Results
A statistically significant interaction (p < 0.01) was observed between MSPs and facial asymmetry. No significant differences were observed among MSPs in the symmetric group. However, significant differences in linear measurements were identified among MSPs in the asymmetric group. Specifically, the upper facial MSP revealed both maxillary and mandibular transverse asymmetries. On the other hand, anterior nasal spine (ANS)-associated MSP could not identify maxillary asymmetry. Furthermore, the menton deviation was approximately 3 mm lower when estimated using the ANS-associated MSP than that using upper facial MSP.
Conclusions
The choice of MSP can significantly affect treatment outcomes while diagnosing patients with asymmetry. Therefore, care should be taken when selecting MSP in clinical practice.

Keyword

Facial asymmetry; Midsagittal plane; Cone-beam computed tomography; Diagnosis

Figure

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  Figure 1 Graphical representation of landmark position. A, frontal view; B, top-down view; C, lateral view; D, clipping-lateral view; E, clipping-frontal view of the left condyle; F, oblique view for dental landmarks. FZS, frontozygomatic suture; N, nasion; Or, orbitale; Mx, maxilla; ANS, anterior nasal spine; Go, gonion; Me, menton; Ba, basion; Po, porion; S, sella; RU1, right upper incisor; RU3, right upper canine; RU6, right upper first molar; RL1, right lower incisor; RL3, right lower canine; RL6, right lower first molar; R, right; L, left.

• 

  Figure 2 Graphical representation of the midsagittal planes (MSPs). A, MSP I; B, MSPs II and III; C, MSPs IV, V and VI. FZS, frontozygomatic suture; N, nasion; FHP, Frankfort horizontal plane; Po, porion; Ba, basion; Or, orbitale; ANS, anterior nasal spine; S, sella; PNS, posterior nasal spine; R, right; L, left.

• 

  Figure 3 Graphical representation of measurement variables. A, transverse distance of landmarks relative to a midsagittal plane; B, maxillary skeletal yaw (other skeletal and dental yaws were calculated similarly according to their definition). Positive signs were assigned to the yaw and transverse distance of median landmarks if they were in the same direction as the menton deviation; C, ramus angles. Mx, maxilla; ANS, anterior nasal spine; RU3, right upper canine; RU6, right upper first molar; U1, upper incisor; LU3, left upper canine; LU6, left upper first molar; MSP, midsagittal plane; Me, menton; Ndev, non-deviated side; Dev, deviated side; R, right; L, left.

• 

  Figure 4 Profile plots of measurement variables among different midsagittal planes (MSPs). A, anterior nasal spine deviation; B, maxillary transverse distance difference relative to the MSP, subtracting the non-deviated side from the deviated side; C, upper incisor deviation; D, maxillary canine transverse distance difference relative to the MSP, obtained by subtracting the non-deviated side from the deviated side; E, maxillary first molar transverse distance difference for the MSP, obtained by subtracting the non-deviated side from the deviated side; F, menton deviation; G, the ramus angle difference relative to the MSP, obtained by subtracting the non-deviated side from the deviated side; H, maxillary skeletal yaw; I, mandibular skeletal yaw; J, maxillary dental yaw; K, mandibular dental yaw. The red line denotes the asymmetric group, whereas the blue line denotes the symmetric group. Error bars indicate 95% confidence intervals for each variable. FZS, frontozygomatic suture; N, nasion; FH, Frankfort horizontal plane; Ba, basion; ANS, anterior nasal spine; S, sella; PNS, posterior nasal spine; Mx, maxilla; Diff, difference; U1, upper incisor; U3, upper canine; U6, upper first molar; Me, menton.

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  Figure 5 Schematic diagrams showing changes in linear measurements relative to various midsagittal planes (MSPs). A, top-down view showing the MSP-yaw of MSP III; B, frontal view showing the MSP-roll of MSP IV. The dotted arrows denote the transverse distance between the first molars and the aforementioned MSPs. Ba, basion; U6, upper first molar; N, nasion; ANS, anterior nasal spine; FH, Frankfort horizontal plane; R, right; L, left.

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