Analysis of Facial Asymmetry

Abstract

Facial symmetry is an important component of attractiveness. However, functional symmetry is favorable to aesthetic symmetry. In addition, fluctuating asymmetry is more natural and common, even if patients find such asymmetry to be noticeable. However, fluctuating asymmetry remains difficult to define. Several studies have shown that a certain level of asymmetry could generate an unfavorable image. A natural profile is favorable to perfect mirror-image profile, and images with canting and differences less than 3°-4° and 3-4 mm, respectively, are generally not recognized as asymmetry. In this study, a questionnaire survey among 434 medical students was used to evaluate photos of Asian women. The students preferred original images over mirror images. Facial asymmetry was noticed when the canting and difference were more than 3° and 3 mm, respectively. When a certain level of asymmetry is recognizable, correcting it can help to improve social life and human relationships. Prior to any operation, the anatomical component for noticeable asymmetry should be understood, which can be divided into hard tissues and soft tissue. For diagnosis, two-and three-dimensional (3D) photogrammetry and radiometry are used, including photography, laser scanner, cephalometry, and 3D computed tomography.

Keywords: Face; Facial asymmetry; Three dimensional image.

Fig. 1. Landmarks on the facial soft tissues. Pp, pupil; O', otobasion inferius; Mc, medial canthus; Ch, cheilion; Go', soft-tissue gonion; Me', softtissue menton; G, glabella; Sn, subnasale; Pr, pronasale; Na', soft-tissue nasion; Pre, preaureculare; MI, midsagittal line; BI, bipupillary line; HI, horizontal line; RI, ramus line; OI, otobasion inferius line; O, oto; GI, gonion line; CI, chin line, Mbl, mandible body line; Pog', pogonion.

Fig. 2. (A) Posteroanterior cephalometric landmarks. 1, external peripheral cranial bone surface; 2, mastoid process; 3, occipital condyle; 4, nasal septum: crista galli, floor of nose; 5, orbital outline: inferior surface of the orbital plate of the frontal bone; 6, oblique outline: innominate line; 7, superior surface of the petrous portion; 8, lateral surface of the frontosphenoid process of zygoma and zygomatic arch (ZA); 9, cross section of zygomatic arch; 10, infratemporal surface of maxilla; 11, mandible: body, rami, coronoid process, condyles; 12, dental unit. (B) Posteroanterior cephalometric landmarks. Om, orbital midpoint, the point of the line connecting the right and left lo (lateral orbitale) at the base of the cristagalli that the highest point on the extenstion of the nasal septum, the reference point of sagittal plan; mo, medial orbitale, the nearest point on the medial orbital margin in median plan; tns, tip of nasal spine; ans, anterior nasal spine, the center point at the base of the nose; iif, incision inferior frontale: the central point of the mandibular central incisors end; isf, incision superior frontale: the central point of the maxillary central incisors end; m, mandibular midpoint; lo, lateral orbitale, lateral orbital margin and innominate line that intersects; lzmf, lateral zygomatic frontal suture; mzmf, medial zygomatic frontal suture; cd, condylion, the hightest point of mandibular condyle; za, most lateral point of zygomatic arch; ma, lowest point of mastoid process; ag, antegonion, the highst point of antegonial notch; mx, maxillare, the line between maxillary alveolar process and inferior point of ztgomatic buttress. Similar with J point; J jugulare (J), the most concave point of zygomatic buttress; um, maxillary molar, the outer surface of the maxillary first molar; lm, mandibular molar, the outer surface of the mandibular first molar; mf, mental foramen; CSP, cental sagittal plan. Draw in several ways, representative example, vertical line of lo-lo line is passing through plotting the om, passing drawing a vertical line of the line connecting the two sides lzmf and zmmf is om.

Fig. 3. Ricketts analysis: based on the draw CSP, and analyzed by measuring the relative distance and angle of the respective measurement points. 1) Nasal cavity width: NC-NC, the distance between the outermost point of the nasal cavity. 2) Mn. width: AG-AG, the distance between antegonial notch. 3) Mx. width: the distance between Z-AG and J. 4) Symmetry the distance between the left and rgith ZA, AG on CSP, the relationship. Between CSP and m, the distance and angle between the left and right J on CSP. 5) Intermolar width: the distance and angle between um and lm on CSP. 6) Intercuspid width: the distance and angle between tip of mandibular canine and CSP. CSP, central sagittal plane; ZA AXIS, zygomatic arch axis; NC, nasal cavity; AG, angle of gonion or gonial notch.

Fig. 4. Grummons analysis. Measurement plane: 1) Z plan: the line connecting the left and right mzmf. 2) ZA plan: the line connecting the left and right za. 3) J plan: the line connecting the left and right J point. 4) Occlusal plan: the line connecting the bite point of the left and right fist molar. 5) AG plan: the line connecting the left and right ag. 6) Menton line: the line parallel to the z plan that passes through the menton.

Fig. 5. Kyungpook National University quick protocol for posterioranterior analysis.

Fig. 6. (A) Analysis of panoramic radiographic: investigation of mandibular symmetry. (B) Analysis of panoramic radiographic: treatment planning, correction of mandibular rolling. The arrow represents the direction of correction for asymmetry. (C) Analysis of panoramic radiographic: paper surgery according to the treatment planning.

Fig. 7. (A-C) Landmarks for three-dimensional computed tomography analysis. Na, nasion; Or, orbitale; Go lat, gonion lateralis; Ag, antegonion; Me, menton; Cd sup, condylion superius; ANS, anterior nasal spine; Cg, crista galli; P, prechiasmatic groove; Op, opisthion.

Fig. 8. Reference plan and rotations for three-dimensional measurement.

Fig. 9. Articular analysis: (A) Face bow transfer. (B) Mounting for upper dental cast. Articular analysis: (C) Frontal view shows pitching of occlual plan. (D) Lateral view shows rolling of occlusal plan. (E) Palatal view of maxillary dental cast, shows yawing of maxilla.

Fig. 10. (A) Mirror image study: left, original composed image; center, right mirrored image; right, left mirrored image. (B) Chin-lip canting study images: most left image, original; most right image, 5° canting. (C) Oral commissure elevation images: most left image, original; most right image, 5 mm elevation.