Three-Dimensional Imaging for Orthognathic Surgery and Orthodontic Treatment

Analysis of hard tissue facial symmetry after unilateral mandibular reconstruction

Background

This study aimed to determine how successful reconstruction of the mandible can recover the symmetry.

Materials and methods

All patients who underwent surgical treatment for unilateral mandibular reconstruction in 4 years were retrospectively examined. Bilateral differences of gonion (GO) positions were measured in 3 dimensions based on immediate postoperative computed tomography. The data collected was analyzed in 3 ways: First, the comparison of bilateral differences of GO in 3 dimensions. Second, the mean Asymmetry Index in control subjects was used to divide all cases into three groups: “Symmetry,” “Asymmetry,” and “Marked asymmetry.” Third, “maximum normal asymmetry” was calculated, and all cases were categorized as below and above maximum normal asymmetry. The difference between two gonial angles was used to determine the amount of asymmetry.

Results

Forty-seven patients and 47 normal adults were enrolled. The mean bilateral GO difference in the control group was higher than in the study group patients, but it was not statistically significant. The mean Asymmetry Index for the control group was not also significantly higher than the study cases. The study group was “Symmetric” in 78.7% of the cases whereas the control group in 91.4%, 19.1% of the study group and 8.5% of controls were “Asymmetric,” and 2.1% of study cases and 0% of controls were “Markedly Asymmetric.” Maximum normal asymmetry was 82.9% in the study group and 97.8% in the control group. The mean differences between the right and left gonial angles were higher in the study group, but it was not significant (P = 0.1).

Conclusions

Our study’s results showed that bilateral symmetry in mandibular reconstruction patients was satisfactory and similar to the normal individuals.

Analysis of Mandibular Structure Using 3D Facial Computed Tomography

Objective

This study measured and analyzed the position and dimension of genial tubercle (GT) and mental foramen (MF)

Study Design

Retrospective chart review study.

Setting

Tertiary care teaching hospital.

Subjects and Methods

Two hundred ten subjects were included who received 3-dimensional (3D) facial computed tomography (CT), and the GT and MF were evaluated. Subjects were divided into 4 groups by gender and skeletal type. Seven variables were measured: (1) height of GT (GTH), (2) width of GT (GTW), (3) distance from apices of lower incisors to superior border of GT (LI-SGT), (4) distance from inferior border of GT to inferior border of mandible (IGT-IBM), (5) thickness of anterior mandible (MT), (6) distance from symphysis of mandible to MF (S-MF), and (7) distance from superior border of GT to inferior border of mandible (SGT-IBM).

Results

All the parameters showed marked differences in individuals. Class I males showed longer GTH, MT, and SGT-IBM than class I females ( P < .05). IGT-IBM and S-MF were longer in class II males than in class I females ( P < .05). LI-SGT and IGT-IBM also showed personal variation.

Conclusion

Anatomical features of mandibular structures showed individual variations. GTH, IGT-IBM, MT, S-MF, and SGT-IBM also showed differences between the groups.

Reproducibility of three-dimensional coordinate systems based on craniofacial landmarks: a tentative evaluation of four systems created on images obtained by cone-beam computed tomography with a large field of view

OBJECTIVES

To propose a method for evaluating the reproducibility of anatomical coordinate systems based on craniofacial skeletal landmarks and to tentatively evaluate four systems created on preoperative cone-beam computed tomography (CBCT) data obtained from mandibular prognathism patients in order to confirm the utility for actual patients' data.

MATERIALS AND METHODS

In three-dimensional images of 10 patients obtained by a CBCT with a large field of view, six dentists set four coordinate systems that were created in different ways, twice by plotting some landmarks situated in the superior portion of the maxillofacial skeletons. The 95% confidence ellipse of six objective landmarks related to the jaw and teeth (upper incisor, left upper first molar, lower incisor, left lower first molar, menton, and left gonion) were three-dimensionally drawn for each coordinate system. The ellipsoid volume was calculated to evaluate the reproducibility of the coordinate systems.

RESULTS

The reproducibility could be evaluated for each coordinate system using the method proposed. The coordinate systems that were created by landmarks situated at greater distances from each other showed relatively small ellipsoid volume in comparison to those with shorter distances between landmarks.

CONCLUSION

Anatomical coordinate systems with larger distances between the landmarks used were stable when landmarks related to the jaw and teeth were assigned as objective landmarks. The method proposed here was effective in terms of the reproducibility evaluation of a coordinate system.

Three-dimensional analysis in facial asymmetry: comparison with model analysis and conventional two-dimensional analysis

The purpose of this study was to compare a computed tomographic (CT) three-dimensional analysis with a model analysis to use it as diagnostic aid for the evaluation of occlusal plane tilting in facial asymmetry. Ten patients with facial asymmetry underwent CT three-dimensional examination, plaster cast analysis, and two-dimensional cephalometric analysis. The distance between a reference plane to the upper first molar and upper canine was measured on three-dimensional CT, on models, and on cephalograms to assess occlusal plane tilting. Measurements taken on three-dimensional CT were compared with those taken on articulator and cephalograms, and the level of discordance between the different analyses was evaluated. Quantitative data on the occlusal tilting are similar, but three-dimensional CT gives a better representation of anatomy, thus reducing interpretative problems about altered individual anatomy. Three-dimensional CT seems to be so helpful in detecting individual anatomical variations that it can be adopted in the diagnosis for severe craniofacial asymmetry.

Evaluation of 2 different reference planes used for the study of asymmetric facial malformations

The purpose of this study was to evaluate if Frankfort plane (FH) and plane passing through the lateral semicircular canals (LS) can be used as reference planes in three-dimensional analysis.Ten patients with facial asymmetry underwent a three-dimensional computed tomography. Computed tomographic images were processed by means of a commercial software and a personal computer to obtain a three-dimensional virtual craniofacial model. The average Frankfort plane and the plane passing through the LS were identified. The distance from the above-mentioned planes to the first upper molar and upper canine cusp was measured.It was not possible to detect an FH plane in any of the patients. Right FH, left FH, average FH, and LS plane were traced. The discrepancies among reference planes were significant in cases with severe asymmetry. A minimal discrepancy was noticed in patients with light asymmetry.In patients with severe asymmetry, the LS plane results in steady, reproducible, detectable, and closer to the patient's anatomy, representing a valid reference plane for three-dimensional computed tomography analysis.

Three-dimensional analysis system for orthognathic surgery patients with jaw deformities

INTRODUCTION

Traditionally, lateral and frontal cephalograms are used with facial photographs to evaluate a patient's maxillofacial skeletal and facial soft-tissue morphology. However, the enlargement and distortion of 2-dimensional radiography made it difficult to accurately conceptualize the patient's anatomy. The purpose of this article was to introduce a new method for comparing 3-dimensional (3D) standard values of the maxillofacial skeletal and facial soft-tissue morphology before and after orthognathic surgery.

METHODS

Normative 3D standard values of the maxillofacial skeletal and facial soft-tissue morphology were calculated from normal women. The pre- and postoperative morphology of one woman who underwent orthognathic surgery was compared with the normative data.

RESULTS

This 3D analysis has clinical value to evaluate patients before and after surgical treatment.

CONCLUSIONS

This quantitative assessment of 3D maxillofacial morphology can evaluate the area and degree of displacement and rotation of the facial skeleton and facial soft tissues. This method is sufficiently useful for routine clinical applications.

Reproducibility of maxillofacial anatomic landmarks on 3-dimensional computed tomographic images determined with the 95% confidence ellipse method

OBJECTIVE

To assess the plotting reproducibility of landmarks on 3-dimensional computed tomography (3D-CT) images through use of the 95% confidence ellipse in order to propose sufficiently stable coordinate systems for 3D-CT measurements.

MATERIALS AND METHODS

Six dentists plotted 19 landmarks twice on 3D-CT images. Scatterplots and the 95% ellipses were produced 3-dimensionally, and the areas of the ellipses were calculated for evaluating the reproducibility of landmarks.

RESULTS

The plotting reproducibility of each landmark showed characteristic features. Among five landmarks (the sella [S], nasion [N], basion [Ba], orbitale [Or], and true porion [Po]) that are frequently used as reference points on cephalograms, Ba showed the smallest areas for all three coordinate axes, indicating high reproducibility. The coronoid process (CP) and the tooth-related landmarks showed relatively high reproducibility.

CONCLUSION

Sufficiently stable coordinate axes could be proposed for different treatments and studies.

3D-CT evaluation of facial asymmetry in patients with maxillofacial deformities

OBJECTIVE

The aims of this study were to characterize the symmetrical features of patients with facial deformities and to suggest a classification system for facial asymmetry based on 3-dimensional-computed tomography (3D-CT) evaluation.

STUDY DESIGN

Preoperative CT images were investigated for 49 patients with maxillofacial deformities. Asymmetry indices were calculated for some landmarks in the maxilla, mandibular body and the mandibular ramus regions.

RESULTS

Asymmetry was observed most frequently in the mandibular body region. The subjects were divided into 3 groups. Subjects without any asymmetry in the 3 regions were classified as Group I (44.9%). Groups II or III were defined for subjects without or with maxillary region asymmetry, respectively, and they were subcategorized. In Group IIA (8.2%), asymmetry was shown solely in the mandibular body region, and in Group IIB (18.4%), additional asymmetry was shown in the mandibular ramus region. Group IIIA (6.1%) showed asymmetry only in the maxillary region, and Group IIIB (22.4%) showed asymmetry in all 3 regions.

CONCLUSION

The 3D-CT classification for facial asymmetry has the potential to replace the conventional cephalometric classification.

Condylar head remodeling following mandibular setback osteotomy for prognathism: A comparative study of different imaging modalities

PURPOSE

Condylar remodeling, which develops after mandibular setback osteotomy, was evaluated and compared in CT, plain film radiographs, and MR images acquired postoperatively.

METHODS

Thirty-nine patients treated with sagittal split ramus osteotomy (SSRO) and 46 patients treated with intraoral vertical ramus osteotomy (IVRO) were studied. Remodeling as seen in the images and the diagnostic agreement between imaging modalities was evaluated.

RESULTS

A newly formed bone layer in the posterior part of the condylar head was identified as a sign suggestive of remodeling. This sign was seen predominantly at periods over 6 months postoperatively. IVRO subjects had a higher incidence of remodeling than did the SSRO group. The diagnostic agreement between the 3 imaging modalities was substantial. There was a positive correlation between postoperative condylar displacement and the incidence of remodeling.

CONCLUSIONS

The incidence of postoperative condylar head remodeling may be predictable. High-dose postoperative imaging studies to assess the TMJ should be restricted to those cases having a clear need for such studies.

Assessment of Three-dimensional X-ray Images: Reconstruction From Conventional Tomograms, Compact Computerized Tomography Images, and Multislice Helical Computerized Tomography Images

Three-dimensional X-ray images (3D images) were used for imaging diagnosis in the oral and maxillofacial region. These images could be fundamentally reconstructed from various tomograms, though clinical 3D images were mainly reconstructed from computerized tomography (CT) images. In this investigation, 3D images were reconstructed from conventional tomograms with a panoramic unit, compact CT images, and multislice helical CT images, and the usefulness of each system was subjectively assessed for dental implant treatment. Three hemilateral dried human mandibles were used and were examined by linear tomography with a panoramic unit, compact CT, and multislice helical CT, and 3D images were reconstructed by using the rendering software for each system. The 3D images were visually evaluated on a 5-point scale covering the alveolar ridge, buccal and lingual bone surface, mental foramen, and tooth sockets. As a result, 3D images reconstructed from conventional tomograms with the panoramic unit were assessed as fair to unsure, compact CT 3D images were assessed as unsure to good, and multislice helical CT 3D images were assessed as good to excellent. It was concluded that compact CT 3D images and multislice helical CT 3D images were useful in dental implant treatment.

3D-CT evaluation of facial asymmetry

OBJECTIVE

Recently, 3-dimensional-computed tomography (3D-CT) imaging has been used in the diagnosis and surgical treatment planning of patients with craniofacial deformities. The present authors have developed a 3D-CT imaging procedure for a 3-dimensional coordinate point evaluation system to assess and diagnose patients with facial asymmetry.

STUDY DESIGN

The CT data of 16 subjects was selected retrospectively as the control group from patients who had undergone CT examinations to diagnose conditions other than maxillofacial deformities. Anatomical landmarks modified from orthodontic craniometric (cephalometric) points were defined on the 3D-CT images and the asymmetry index of each point was calculated in millimeters. A diagrammatic chart with a baseline indicating the mean asymmetry indices plus the standard deviation in the control group was designed. The resulting diagrammatic chart was used to evaluate the degree of deformity in facial asymmetry patients.

RESULTS AND CONCLUSIONS

The topography of facial asymmetry was assessed. The 3D-CT imaging technique as described herein is a practical method of evaluating the morphology of facial asymmetry.

3D CT evaluation of masseter muscle morphology after setback osteotomy for mandibular prognathism

OBJECTIVE

Following mandibular setback osteotomy, changes in the direction, length, and cross-sectional area of the masseter muscle were studied by means of computerized tomography (CT) images generated with a 3-dimensional (3D) reconstructive technique.

STUDY DESIGN

Pre- and postoperative CT examinations were performed on 17 prognathic patients treated by sagittal split ramus osteotomy with rigid osteosynthesis and 13 patients treated by intraoral vertical ramus osteotomy without osteosynthesis. The pre- and postoperative masseter muscle direction and length were evaluated using 3D CT images observed from a lateral viewing angle. The cross-sectional area of the masseter muscle was first measured on an axial CT image of a selected slice level, following which the right-angle cross-sectional area of the muscle was revised using the measured area from the axial image.

RESULTS

Postoperatively, anterior tilting of the masseter muscle was observed; however, masseter muscle length was unchanged. Three months postoperatively, a significant reduction in the cross-sectional area of the masseter muscle was seen. A tendency to revert back to the normal dimension was seen between 6 months and 1 year postoperatively. No significant difference was noted between the 2 surgical techniques.

CONCLUSIONS

Three-dimensional computed tomography is an adequate imaging modality for masseter muscle evaluation. The results of this study suggest the masseter muscle may undergo reversible atrophy after mandibular setback osteotomy.