Korean J Orthod.  2022 Mar;52(2):85-101. 10.4041/kjod.2022.52.2.85.

Characterization of facial asymmetry phenotypes in adult patients with skeletal Class III malocclusion using three-dimensional computed tomography and cluster analysis

• Ha SW
• Kim SJ
• Choi JY
• Baek SH

• KMID: 2527453
• DOI: http://doi.org/10.4041/kjod.2022.52.2.85

Abstract

Objective
To classify facial asymmetry (FA) phenotypes in adult patients with skeletal Class III (C-III) malocclusion.
Methods
A total of 120 C-III patients who underwent orthognathic surgery (OGS) and whose three-dimensional computed tomography images were taken one month prior to OGS were evaluated. Thirty hard tissue landmarks were identified. After measurement of 22 variables, including cant (°, mm), shift (mm), and yaw (°) of the maxilla, maxillary dentition (Max-dent), mandibular dentition, mandible, and mandibular border (Man-border) and differences in the frontal ramus angle (FRA, °) and ramus height (RH, mm), K-means cluster analysis was conducted using three variables (cant in the Max-dent [mm] and shift [mm] and yaw [°] in the Manborder). Statistical analyses were conducted to characterize the differences in the FA variables among the clusters.
Results
The FA phenotypes were classified into five types: 1) non-asymmetry type (35.8%); 2) maxillary-cant type (14.2%; severe cant of the Max-dent, mild shift of the Man-border); 3) mandibularshift and yaw type (16.7%; moderate shift and yaw of the Man-border, mild RH-difference); 4) complex type (9.2%; severe cant of the Max-dent, moderate cant, severe shift, and severe yaw of the Man-border, moderate differences in FRA and RH); and 5) maxillary reverse-cant type (24.2%; reverse-cant of the Max-dent). Strategic decompensation by pre-surgical orthodontic treatment and considerations for OGS planning were proposed according to the FA phenotypes.
Conclusions
This FA phenotype classification may be an effective tool for differential diagnosis and surgical planning for Class III patients with FA.

Keyword

Facial asymmetry; Class III malocclusion; Cluster analysis

Figure

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  Figure 1 The landmarks used in this study. A, Nasion (N), frontozygomatic point, (FZP, R and L), porion (Po, R and L), orbitale (Or, R and L), mesiobuccal (MB) cusp tip of the mandibular first molar (L6CP, R and L), lower dental midline point (L1MP), inferior gonion (Inf-Go, R and L), and menton (Me). B, A point (A), jugal process point (J, R and L), mandibular foramen (MdF, R and L), MB cusp tip of the maxillary first molar (U6CP, R and L), B point (B), and upper dental midline point (U1MP). C and D, Condylion (Cd-S, R and L), lateral pole of condyle (Cd-L, R and L), medial pole of condyle (Cd-M, R and L), and condylar center (Cd-C, R and L). R, right; L, left.

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  Figure 2 The planes and lines used in this study. A, Horizontal plane, coronal plane, mid-sagittal (MidS) plane, frontozygomatic point (FZP) line, right Frankfort horizontal (RFH) line, and ramal line (R and L). B, Condylar sagittal plane (R and L) and condylar axis line (R and L). C, Condylar coronal plane (R and L). R, right; L, left. See Figure 1 for definitions of the other landmarks.

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  Figure 3 The variables used in this study. Maxillary skeletal (MxS)-Cant (°), MxS-Cant (mm), MxS-Shift (mm), MxS-Yaw (°), maxillary dental (MxD)-Cant (°), MxD-Cant (mm), MxD-Shift (mm), MxD-Yaw (°), mandibular dental (MdD)-Cant (°), MdD-Cant (mm), MdD-Shift (mm), MdD-Yaw (°), mandibular skeletal (MdS)-Cant (°), MdS-Cant (mm), MdS-Shift (mm), MdS-Yaw (°), mandibular border (MdB)-Cant (°), MdB-Cant (mm), MdB-Shift (mm), MdB-Yaw (°), frontal ramus angle (FRA, °) (R and L, difference), Ramus height (RH, mm) (R and L, difference). MidS, mid-sagittal; R, right; L, left. See Figure 1 for definitions of the other landmarks.

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  Figure 4 Examples of the non-asymmetry type and 4 facial asymmetry phenotypes. 1) Non-asymmetry type (35.8%); 2) maxillary-cant (Max-Cant) type (14.2%; severe cant of the maxillary dentition, mild shift of the mandibular border); 3) mandibular-shift and yaw (Man-Shift-Yaw) type (16.7%; moderate shift and yaw of the mandibular border, mild ramus height difference); 4) complex type (9.2%; severe cant of the maxillary dentition, moderate cant, severe shift, and severe yaw of the mandibular border, moderate differences in frontal ramus angle and ramus height); and 5) maxillary reverse-cant (Max-Rev-Cant) type (24.2%; reverse-cant of the maxillary dentition).

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  Figure 5 Flow chart that explains the characteristics of the facial asymmetry phenotypes in skeletal Class III patients who underwent orthognathic surgery. Max-Cant, maxillary-cant; Man-Shift-Yaw, mandibular-shift and yaw; Max-Rev-Cant, maxillary reverse-cant; FRA, frontal ramus angle; RH, ramus height.

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  Figure 6 Strategic decompensation and surgical planning according to the facial asymmetry phenotypes. Max-Cant, maxillary-cant; Man-Shift-Yaw, mandibular-shift and yaw; Max-Rev-Cant, maxillary reverse-cant; TAD, temporary anchorage device; IPW, inter-premolar width; IMW, inter-molar width; 3D, three-dimensional.

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