Sang-Hwy Lee

Three-dimensional computed tomography analysis of mandibular morphology in patients with facial asymmetry and mandibular prognathism

INTRODUCTION The purpose of this study was to investigate the dimensional changes in each skeletal unit in the mandibles of patients with facial asymmetry and mandibular prognathism. METHODS The patients consisted of 50 adults with mandibular prognathism, divided into the symmetry group (n = 20) and the asymmetry group (n = 30) according to the degree of menton deviation. Three-dimensional computed tomography scans were obtained with a spiral computed tomography scanner. Landmarks were designated on the reconstructed 3-dimensional surface models. The lines to represent condylar, coronoid, angular, body, and chin units were used. Ramal and body volumes were measured in the hemi-mandibles. RESULTS In the asymmetry group, condylar and body unit lengths were significantly longer, and coronoid unit length was significantly shorter on the nondeviated side than on the deviated side (P <0.01). Angular and chin unit lengths were not significantly different between the 2 sides (P >0.05). Ramal volume was significantly greater on the nondeviated side (P <0.01), but body volume was not significantly different between the 2 sides (P >0.05). CONCLUSIONS Both condylar and body units appeared to contribute to mandibular asymmetry, with a more central role of the condylar unit.

Integration accuracy of digital dental models and 3-dimensional computerized tomography images by sequential point- and surface-based markerless registration

OBJECTIVE The goal of this study was to evaluate the accuracy of the integration of computerized tomography (CT)-based bone models and laser-scanned dental models by sequential point- and surface-based markerless registration to create a digital maxillofacial-dental model. STUDY DESIGN The integration accuracy was evaluated in normal skulls (group I) and subjects with maxillofacial deformities (group II) by measuring the distance between the integrated models (for group I and II) and between the final integrated model and the laser-scanned original skull model (for group I). RESULTS The average error ranged between 0 and 0.2 mm without statistically significant difference in the region of maxilla or mandible and in tooth location. CONCLUSIONS We could confirm that the integration can be made with good accuracy without the aid of fiducial markers for the maxillofacial-dental composite model from the different resolution of CT and dental models.

Clinical experiences of digital model surgery and the rapid-prototyped wafer for maxillary orthognathic surgery

OBJECTIVE The aim of this study was to present our clinical experience regarding the production and accuracy of digitally printed wafers for maxillary movement during the bimaxillary orthognathic surgery. STUDY DESIGN Fifty-five consecutive patients requiring maxillary orthognathic surgery were included in this study. The plan for digital model surgery (DMS) was dictated by the surgical plans for each clinical case. We carried out digital model mounting, DMS, wafer printing, and confirmation of the accuracy of the procedure. RESULTS Moving the reference points to the target position in DMS involved a mean error of 0.00-0.09 mm. The mean errors confirmed by the model remounting procedure with the printed wafer by DMS were 0.18-0.40 mm (for successful cases; n = 42) and 0.03-1.04 mm (for poor cases; n = 3). CONCLUSION The accuracies of the wafers by DMS were similar to those for wafers produced by manual model surgery, although they were less accurate than those produced by DMS alone. The rapid-prototyped interocclusal wafer produced with the aid of DMS can be an alternative procedure for maxillary orthognathic surgery.

Morphologic relationship between the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism

INTRODUCTION This study was conducted to measure the dimensional changes in the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism, and to examine the morphologic relationship between asymmetries of the cranial base and the mandible. METHODS The patients were 60 adults with mandibular prognathism, divided into a symmetry group (menton deviation, <2 mm; n = 30) and an asymmetry group (menton deviation, >4 mm; n = 30) according to the degree of menton deviation. Three-dimensional computed tomography scans were obtained with a spiral scanner. Landmarks were designated on the reconstructed 3-dimensional surface models. Linear, angular, and volumetric measurements of the cranial base and mandibular variables were made. RESULTS In the asymmetry group, the hemi-base, anterior cranial base, and middle cranial base volumes were significantly larger (P <0.01), and crista galli to sphenoid, sphenoid to petrous ridge, anterior clinoid process to petrous ridge, and vomer to petrous ridge lengths were significantly longer (P <0.05) on the nondeviated side than on the deviated side. Menton deviation was significantly correlated with the difference in hemi-base volume, and ramal volume was significantly correlated with the difference in hemi-base and middle cranial base volumes between the nondeviated and deviated sides (P <0.05). CONCLUSIONS In patients with facial asymmetry and mandibular prognathism, cranial base volume increased on the nondeviated side and was also correlated with mandibular asymmetry.

Architectural characteristics of the normal and deformity mandible revealed by three-dimensional functional unit analysis.

The 3D architecture of the mandible contributes to the functional and morphological characteristics of the lower one third of craniofacial region. The mandible has six distinct functional units, and its architecture is the sum of balanced growth of each functional unit and surrounding matrix. A dentofacial deformity (DFD) with malocclusion can be interpreted as their unbalanced growth. In order to characterize the mandibular 3D architecture, we analyzed the 3D reconstructed computed tomography (CT) images in terms of functional units. We evaluated both sides of 30 datasets of 3D CT scans of normal controls (N = 6) and patients with prognathic (N = 17) or retrognathic (N = 7) mandibles. We first identified and evaluated reference points to define mandibular functional units and compared their linear and angular measurements of DFD with normal group. The condylar and body length, the ratio of condyle/coronoid length, and the condylar head axis angle showed the statistically significant differences between groups. From these results, we could define the 3D reference points for functional units and identify the 3D architectural characteristics of DFD mandibles. These models may help us improve diagnosis and treatment planning to let them return to the normal and balanced architecture for DFD.

Accurate computerised mandibular simulation in orthognathic surgery: a new method for integrating the planned postoperative occlusion model.

Department of Oral and Maxillofacial Surgery, National Health Insurance Corporation Ilsan Hospital, 1232, Baekseok-dong, Ilsan-donggu, Goyang-si, yeonggi-do, 410-719, Republic of Korea Department of General Dentistry, Dental Hospital, Yonsei University, 134 Shinchon-dong, Seodaemun-Ku, Seoul, 120-752, Republic of Korea Department of Oral & Maxillofacial Surgery, College of Dentistry, Yonsei University, 134 Shinchon-dong, Seodaemun-Ku, Seoul, 120-752, epublic of Korea

Early orthognathic surgery with three-dimensional image simulation during presurgical orthodontics in adults.

To correct dentofacial deformities, three-dimensional skeletal analysis and computerized orthognathic surgery simulation are used to facilitate accurate diagnoses and surgical plans. Computed tomography imaging of dental occlusion can inform three-dimensional facial analyses and orthognathic surgical simulations. Furthermore, three-dimensional laser scans of a cast model of the predetermined postoperative dental occlusion can be used to increase the accuracy of the preoperative surgical simulation. In this study, we prepared cast models of planned postoperative dental occlusions from 12 patients diagnosed with skeletal class III malocclusions with mandibular prognathism and facial asymmetry that had planned to undergo bimaxillary orthognathic surgery during preoperative orthodontic treatment. The data from three-dimensional laser scans of the cast models were used in three-dimensional surgical simulations. Early orthognathic surgeries were performed based on three-dimensional image simulations using the cast images in several presurgical orthodontic states in which teeth alignment, leveling, and space closure were incomplete. After postoperative orthodontic treatments, intraoral examinations revealed that no patient had a posterior open bite or space. The two-dimensional and three-dimensional skeletal analyses showed that no mandibular deviations occurred between the immediate and final postoperative states of orthodontic treatment. These results showed that early orthognathic surgery with three-dimensional computerized simulations based on cast models of predetermined postoperative dental occlusions could provide early correction of facial deformities and improved efficacy of preoperative orthodontic treatment. This approach can reduce the decompensation treatment period of the presurgical orthodontics and contribute to efficient postoperative orthodontic treatments.

Metal artifact reduction in CT by identifying missing data hidden in metals

There is increasing demand in the field of dental and medical radiography for effective metal artifact reduction (MAR) in computed tomography (CT) because artifact caused by metallic objects causes serious image degradation that obscures information regarding the teeth and/or other biological structures. This paper presents a new MAR method that uses the Laplacian operator to reveal background projection data hidden in regions containing data from metal. In the proposed method, we attempted to decompose the projection data into two parts: data from metal only (metal data), and background data in the absence of metal. Removing metal data from the projections enables us to perform sparsity-driven reconstruction of the metal component and subsequent removal of the metal artifact. The results of clinical experiments demonstrated that the proposed MAR algorithm improves image quality and increases the standard of 3D reconstruction images of the teeth and mandible.

Accuracy assessment of image-based surface meshing for volumetric computed tomography images in the craniofacial region.

Background Three-dimensional printing and computer-assisted surgery demand a high-precision three-dimensional mesh model created from computed tomography (CT) imaging data using an image-based meshing algorithm. We aimed to evaluate the three-dimensional geometric accuracy of surface meshes produced from CT images with commercially available software packages. Methods The CT images were acquired for 3 human dry skulls and 10 manufactured plastic skulls. Four commercially available software packages were used to produce the surface meshes in stereolithography (STL) file format. These CT-based STL surface meshes were registered and compared with three-dimensional optical-scanned reference mesh surface for evaluating the accuracy of the STL mesh produced with each software package. Results The surface geometries produced by the CT-image–based meshing process were all relatively accurate; differences from the three-dimensional optical-scanned data were in the voxel or subvoxel range. However, when comparisons with the three-dimensional optical-scanned surface data were performed in individual anatomic regions, we found significantly different accuracies of the CT-based STL surface meshes produced by the different software packages. Conclusions We found that all 4 software packages showed reasonably good meshing accuracies for clinical use. However, the range of errors inherent in the CT-image–based meshing process demands that caution should be taken in selecting and manipulating the software to avoid potential errors in specific clinical applications.

Three-dimensional vector analysis of mandibular structural asymmetry

OBJECTIVES The three-dimensional (3D) asymmetric structure of the mandible makes it necessary to analyze both its size and angle. Currently the developing 3D analysis techniques are not able to perform the simultaneous linear and angular measurements. Our aim was to evaluate mandibular asymmetry using a vector-based system by constructing 3D vectors for the mandibular functional units. MATERIAL AND METHODS We analyzed the 3D computed tomography images of normal control (N = 27) and asymmetric mandibles (N = 40). We created 3D vectors for the condylar, coronoid, body, gonial, and symphyseal functional units and compared the corresponding pairs of 3D vectors by calculating vector operations. RESULTS The vector difference and other vector components represented the individual 3D architectural pattern and severity of the asymmetric mandible. The body unit contributed most to mandibular asymmetry followed by the condylar unit. CONCLUSIONS The results indicate that 3D vector analysis can improve our understanding of the 3D architecture of asymmetric mandibles. This type of 3D vector analysis can be a useful tool for the comprehensive evaluation of its asymmetric mandibular structure.