Maxillofacial 3-dimensional image analysis for the diagnosis of facial asymmetry

doi:10.1016/j.ajodo.2005.02.021

American Journal of Orthodontics and Dentofacial Orthopedics

Volume 130, Issue 6, December 2006, Pages 779-785

https://doi.org/10.1016/j.ajodo.2005.02.021 Get rights and content

The advent of computed tomography has greatly reduced magnification errors from geometric distortions that are common in conventional radiographs. Recently introduced 3-dimensional (3D) software enables 3D reconstruction and quantitative measurement of the maxillofacial complex; 3D images are also useful in understanding asymmetrical structures. This article describes the use of 3D images in the diagnosis of facial asymmetry. A step-by-step procedure for 3D analysis developed by the authors is described by using the example of a 23-year-old man with a chin deviation to 1 side.

Section snippets

Material and methods

A 23-year-old Korean man had a skeletal Class III malocclusion and a posterior crossbite on the left side. His chief complaint was a deviated chin. The cause of the chin deviation seemed to be the difference between the right and left lengths of the ramus (ie, greater ramus length on the right side, due to a discrepancy in condylar growth). To identify the asymmetry, a PA cephalometric radiograph was obtained and analyzed. Unexpectedly, a discrepancy in the ramus length was not evident,

Results

The measurements were recorded in columns showing the right and the left values, respectively, and the difference for each pair was recorded in a third column by using the following symbols: = to indicate approximately the same values, ≥ or ≤ to indicate an insignificant difference, and > or < to indicate a significant difference. The V Works program displays the measurement outcome and a summary analysis, as shown in Figure 5. For this patient, all measurements showed greater values on the

Discussion

When this patient presented with facial asymmetry, we noticed that the chin deviated to the left side and immediately assumed that the right ramus length was longer. Although the difference of ramus length is generally expressed as a right and left difference in the vertical position of antegonion on PA cephalographs, the difference in the vertical position of antegonions was not significant in this patient. This suggested that another structural discrepancy created the deviation. Thus, to

Conclusions

Both 3D and 2D images are useful to better understand asymmetrical structures. Although most patients with facial asymmetry are well diagnosed by using cephalometric radiographs, some occasions require 3D imaging analysis to obtain more accurate information. By observing and accurately gauging the factors that contribute to chin deviation, 3D imaging analysis will enable us to comprehend its cause more accurately. Furthermore, this type of imaging analysis can be an invaluable tool to determine

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Based on menton deviation (MD), twenty-four subjects were divided into: mild-asymmetry group (n=12) and moderate-to-severe-asymmetry group (n = 12). CBCT images were superimposed with 3D facial photographs. Distance from the midsagittal plane to the outermost point of soft-tissue and hard-tissue were measured and calculated soft-tissue thickness. Comparison of soft-tissue thickness between deviated and contralateral side at any anatomical levels were performed within group, and correlation between bilateral soft-tissue thickness subtractions (soft-tissue compensation) and MD values was evaluated.
Within group, Soft- and hard-tissue distances were greater in deviated side than contralateral side at any levels. In moderate-to-severe group, significant differences were found at gonion and body of mandible level, whereas soft-tissue thickness was only found to be higher on deviated side at the level of mandibular ramus. Soft tissue compensation was negatively correlated with MD value at level of mandibular ramus (R = −0.5, P < 0.05).
Asymmetry was found to be larger in the lower third of the face and was notably remarkable in the moderate-to-severe group. Soft-tissue thickness was thicker on the deviated side of the mandibular ramus. Thus, the soft-tissue compensation seems to be minimized in patients with more severe asymmetry.
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The data collection consisted of 92 archeological skeletal remains of children’s mandibles between 1 and 12 years old. The mandibles were digitalized with a computed tomography (CT) scan, and three dimensional models were obtained. V_hemimandible was calculated using the optimal symmetry plane. The volumes were used to calculate the asymmetry index (AI). Mandibles with an AI of ≥ 3% (N = 9) and a sample of the most symmetrical mandibles (N = 9) were selected for this research. Three groups were created: a symmetrical, an asymmetrical and a pooled group. Micro-CT was used to measure the vBMD and T_cortex in four volumes of interest. The AI was calculated for these parameters as well.
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Seventy-five adult patients aged from 18 to 35 years were included and divided into 3 groups on the basis of sagittal skeletal pattern and chin deviation: skeletal Class I symmetry group, skeletal Class II symmetry group, and skeletal Class II asymmetry group (25 patients per group). Mandibular measurements on cone-beam computed tomography images were performed, and the differences between 2 sides in each group and the differences among the 3 groups were investigated.
Compared with the contralateral side, the deviated side of patients in the Class II asymmetry group showed significantly smaller condyle angle to midsagittal plane, condylar height, ramal length, and length of the mandibular body, whereas it showed a significantly larger distance from condylion to the midsagittal plane, ramus angle to the horizontal plane, and distance from gonion to the midsagittal plane. Most linear measurements in the Class II symmetry group were significantly smaller than those in the Class I symmetry group. These linear measurements on the contralateral side of the Class II asymmetry group showed no significant difference with the Class I symmetry group, and these measurements on the deviated side of the Class II asymmetry group showed no significant difference with the Class II symmetry group.
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Clinician’s cornerMaxillofacial 3-dimensional image analysis for the diagnosis of facial asymmetry

Section snippets

Material and methods

Results

Discussion

Conclusions

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

Am J Orthod Dentofacial Orthop

Am J Orthod Dentofacial Orthop

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

A posteroanterior cephalometric evaluation of craniofacial asymmetry

Angle Orthod

A frontal asymmetry analysis

J Clin Orthod

Development of posteroanterior cephalometric analysis for the diagnosis of facial asymmetry

J Korean Dent Assoc

Enlargement and distortion in cephalometric radiography: compensation tables for linear measurements

Angle Orthod

The cephalometric projection: part IIPrinciples of image distortion in cephalography

Dentomaxillofac Radiol

Clinician’s corner
Maxillofacial 3-dimensional image analysis for the diagnosis of facial asymmetry