Application of cone bean computed tomography to analyze craniofacial asymmetry
Date Issued
2009
Date
2009
Author(s)
Huang, Yu-Chun
Abstract
Objectives: Craniofacial asymmetry is a common feature in human. Orthodontic treatment combined with orthognathic surgery would be suggested in some extreme cases. In the past, 2D images, such as posterioanterior cephalogram or panoramic film, were used as the diagnostic tools to determinate the asymmetric component in craniofacial area. Since the cone beam CT (CBCT) was developed, 3D image would be available in our daily practice. The objectives of this research were to evaluate the reproducibility of landmark identification and the reliability of measurement in CBCT. Next, we developed a screening strategy for analyzing different types of facial asymmetry. ethod: Part I, 17 linear dimensions of 3 dry skulls measured by digital caliper were used as gold standards. Hard copies of manual tracing, computer-aided digital measurements (Winceph 8.0) of both lateral and PA cephalograms, and 3D direct measurements in CBCT (i-CAT/ Simplant Pro 12.02) images were compared with the gold standards. Interclass correlation coefficient was used to evaluate the reliability and magnification in different modalities. Part II. The CBCT data of 33 subjects was collected in this study and classified into 2 groups. The subjects in group 1 showed acceptable level of asymmetry and the amount of Gn deviation to midsagittal line was less than 4mm in frontal cephalogram. Those in group 2 showed obvious asymmetry with Gn deviation more than 4mm. In 3D dataset, the midsagittal plane was determinated as the plane passing ANS, Cg and Ba. Other 11 landmarks were identified and their coordinates were recorded. The differences of the distances between landmarks to reference plane bilaterally were calculated in 3 dimensions. Questionnaire was used to evaluate the subjective opinion of orthodontist at different training levels. Binary regression analysis and cluster analysis (PAM) were used for statistical analyses. esult: Part I, three modalities in our study all showed statistically significant correlation with gold standard. However, the highest one was CBCT, and manual tracing was the least. Part II, binary regression model showed that the predictors for grouping of facial asymmetry included △HCo, △Area 1, △Area 2, APJr and △HCo-Go. In cluster analysis, all subjects were classified into 5 clusters. The most symmetric cases were grouped into cluster (5)-1. The cluster(5)- 3 and cluster(5)- 5 were obvious asymmetric cases with different characteristics. The severity of asymmetry was moderate in cluster(5)-2 without obvious compensated components. In cluster(5)- 4, the major asymmetric component was the difference of area 2, but other variables compensated the manifestation of asymmetry. In the result of questionnaire, the residents in orthodontic department showed higher tendency than specialists and interns in identifying facial asymmetry and suggesting patients to receive orthognathic surgery. On the other hand, GAM proved the 4mm deviation of Gn as a proper threshold to identify the facial asymmetry for its adequacy. Moreover, according to the binary regression model, the factors responsible for the suggestion of orthognathic surgery included the amount of chin deviation, training level of doctors, clustering category and the presence of maxillary canting.onclusion: The reliability of measurement in Winceph system and in CBCT had high correlation with virtual value. The cluster analysis could be applied to classify the patients with facial asymmetry for diagnosis and treatment planning.ey words: cone bean computed tomography, craniofacial asymmetry, cephalometric analysis, 3D image, cluster analysis
Subjects
cone bean computed tomography
craniofacial asymmetry
cephalometric analysis
3D image
cluster analysis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-98-R95422023-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):379920290fa601a894dbfa12d3f94600