Hyeon-Shik Hwang

Ethnic differences in the soft tissue profile of Korean and European-American adults with normal occlusions and well-balanced faces.

Orthodontic diagnosis typically includes comparing a patients cephalometric measurements to standard values. Lateral cephalometric norms, however, may be specific to an ethnic group and cannot always be applied to other ethnic types. The purpose of this study was to compare the soft tissue profiles obtained from Korean and European-American adults with normal occlusions and well-balanced faces, in order to understand the ethnic differences in the soft tissue profile between these two ethnic groups. The lateral cephalograms of 60 Korean (30 men and 30 women) and 42 European-American adults (15 men and 27 women) were traced and digitized by one investigator. Ten angular measurements of facial form and seven linear and angular measurements of lip position were computed. A comparison of the slope of the forehead showed no significant differences between the two groups. The Korean sample, however, had a lower angle of nasal inclination and a higher degree of lip protrusion compared to the European-American adults. Chin protrusion of the Koreans was less prominent than that of the European-Americans. These differences between ethnic groups should be taken into consideration when formulating an orthodontic treatment plan for patients of varying ethnic backgrounds.

Factors associated with initial stability of miniscrews for orthodontic treatment.

INTRODUCTION The purpose of this study was to investigate various factors associated with initial miniscrew stability for the prediction of the success rate. METHODS A total of 378 miniscrews in 154 patients were examined by reviewing their charts. Potential confounding variables examined were age, sex, jaw (maxilla or mandible), placement site, tissue mobility (firm or movable tissue), type, length, and diameter of the miniscrew, and the number of previous operations. The outcome variable of this study was initial stability, defined as the stability of the miniscrew from placement to orthodontic force application. We used the generalized estimating equations method to estimate the influence of each factor on stability for the correlated outcomes of each patient. RESULTS The overall success rate was 83.6% for all miniscrews (316 of 378). After adjusting for the type of miniscrew, the relative success rate in the mandible was 0.48 times that in the maxilla but without statistical significance (crude odds ratio = 0.52, P = 0.13; adjusted odds ratio = 0.48, P = 0.09). There was no statistically significant association of any factors in this model with respect to initial stability. CONCLUSIONS These results suggest that initial stability cannot be guaranteed or predicted. For this reason, any treatment plan should consider the possibility of failure.

Facial Soft Tissue Thickness Database for Craniofacial Reconstruction in Korean Adults

Abstract:  One hundred Korean adults (50 men, 50 women) were scanned in the upright position using a cone‐beam CT (CBCT) scanner. The soft tissue (ST) thicknesses were measured at 31 landmarks, 10 midline and 21 bilateral landmark sites, and the means and standard deviations were obtained for male and female subjects. While 18 of 31 landmarks showed sex differences, the majority showed higher values for male subjects with the exception of a few landmark sites corresponding to the zygoma area, which showed smaller values in men than in women. The mandibular area showed greater differences between the right and left sides. Overall, the ST thickness measurements obtained in this study can be used as a database for the forensic craniofacial reconstruction of Korean adult faces.

Surface Modification of Orthodontic Wires with Photocatalytic Titanium Oxide for its Antiadherent and Antibacterial Properties

OBJECTIVE To test the antiadherent and antibacterial properties of surface modification of orthodontic wires with photocatalytic titanium oxide (TiO(2)). MATERIALS AND METHODS TiO(2) was coated on the surface of the orthodontic wires by a sol-gel thin film dip-coating method. Bacterial adhesion to the wires was evaluated by the weight change of the wires. The antibacterial activity of the surface-modified orthodontic wires was demonstrated by the dilution agar plate method for Streptococcus mutans and spectrophotometry for Porphyromonas gingivalis. RESULTS The orthodontic wires coated with the photocatalytic TiO(2) showed an antiadherent effect against S. mutans compared with the uncoated wires. The bacterial mass that bound to the TiO(2)-coated orthodontic wires remained unchanged, whereas that of the uncoated wires increased by 4.97%. Furthermore, the TiO(2)-coated orthodontic wires had a bactericidal effect on S. mutans and P. gingivalis, which cause dental caries and periodontitis, respectively. The antiadherent and antibacterial mechanisms of TiO(2) to break down the cell wall of those bacteria were revealed by scanning electron microscopy. CONCLUSION The surface modification of orthodontic wires with photocatalytic TiO(2) can be used to prevent the development of dental plaque during orthodontic treatment.

An Accuracy Assessment of Forensic Computerized Facial Reconstruction Employing Cone‐Beam Computed Tomography from Live Subjects

Abstract:  The utilization of 3D computerized systems has allowed more effective procedures for forensic facial reconstruction. Three 3D computerized facial reconstructions were produced using skull models from live adult Korean subjects to assess facial morphology prediction accuracy. The 3D skeletal and facial data were recorded from the subjects in an upright position using a cone‐beam CT scanner. Shell‐to‐shell deviation maps were created using 3D surface comparison software, and the deviation errors between the reconstructed and target faces were measured. Results showed that 54%, 65%, and 77% of the three facial reconstruction surfaces had <2.5 mm of error when compared to the relevant target face. The average error for each reconstruction was −0.46 mm (SD = 2.81) for A, −0.31 mm (SD = 2.40) for B, and −0.49 mm (SD = 2.16) for C. The facial features of the reconstructions demonstrated good levels of accuracy compared to the target faces.

Bone density measurement in interdental areas with simulated placement of orthodontic miniscrew implants.

INTRODUCTION The purposes of this study were to determine bone density at various orthodontic implant sites and compare them according to depth and area (anterior and posterior, buccal and lingual, and maxilla and mandible). METHODS Maxillofacial computed tomography scan data were obtained from 30 adults with normal occlusion. Bone density was recorded in Hounsfield units with simulated placement of miniscrews with the V-Implant program (CyberMed, Seoul, Korea). Bone density was measured to a depth of 6 mm at 1-mm intervals in 60 interdental areas (30 in the maxilla, 30 in the mandible), and mean bone density was calculated at each site. RESULTS Bone density tended to decrease with increasing depth, particularly in the posterior area. Mean bone density showed a progressive increase from posterior to anterior except for the mandibular buccal side, which had no significant differences. A comparison of the mean bone densities between the buccal and lingual sides in the mandible showed that the lingual side had higher values in the anterior area and vice versa in the posterior area. On the other hand, there were no distinct differences between the buccal and lingual sides in the maxilla. A comparison of the mean bone densities between the maxilla and the mandible showed higher values in the mandible, and these differences were more significant on the buccal side of the posterior. CONCLUSIONS The differences in bone densities according to depth and area should be considered when selecting and placing miniscrew implants for orthodontic anchorage.

Registration accuracy in the integration of laser-scanned dental images into maxillofacial cone-beam computed tomography images

INTRODUCTION A precision 3-dimensional (3D) head model can be fabricated by integrating a digital dental model into a maxillofacial 3D image. The integration requires accurate registration of 2 image modalities. The aims of this study were to determine the registration errors for implementation of laser-scanned dental images into cone-beam computed tomography (CBCT) scan data and to examine the influence of the registration area on the accuracy of registration. METHODS The CBCT scans were obtained from 30 adults, and the maxillofacial 3D images were reconstructed. Maxillary and mandibular dental casts were taken from the same subjects and scanned with a 3D laser scanner. The laser-scanned maxillary and mandibular dentition images were incorporated into the CBCT images of each arch in 3 ways according to the registration area: only the buccal surfaces, only the lingual surfaces, and both the buccal and lingual surfaces. Surface-based registration was performed by using an iterative closest point algorithm, and its errors were evaluated by measuring the 3D Euclidean distances between the surface points on the 2 images. RESULTS The registration errors ranged from 0.27 to 0.33 mm. The mandibular arch did not show significant differences in registration errors according to the selected area for the registration. The maxillary arch, however, showed significant differences according to the registration area. When the lingual surfaces only were used for registration, the errors were greater than for the other 2 methods. The errors were least when both the buccal and lingual surfaces were used for registration. CONCLUSIONS The results of this study indicate that accuracy in the integration of laser-scanned dental images into the maxillofacial CBCT images increases when a broad area is used for registration.

Maxillofacial characteristics affecting chin deviation between mandibular retrusion and prognathism patients

OBJECTIVE To examine and compare the maxillofacial characteristics affecting chin deviation three-dimensionally in facial asymmetry patients with mandibular retrusion and mandibular prognathism. MATERIALS AND METHODS Maxillofacial computed tomography (CT) scan data were obtained from 48 orthognathic surgery patients (24 cases of mandibular retrusion and 24 cases of mandibular prognathism) with facial asymmetry. Although chin deviation was assessed on the basis of the ANS-to-menton line on frontal cephalograms, its contributing factors were evaluated on three-dimensional CT images. Maxillary height, ramus length, frontal ramal inclination, lateral ramal inclination, mandibular body length, and body height were defined on each side, and right-left differences were calculated and analyzed. RESULTS In an assessment of chin deviation, subjects in this study showed predominantly left side deviation regardless of the group, and the degree of menton deviation did not reveal significant differences between groups. In a comparison of right-left differences in contributing factors, all values were noted to be greater in the retrusion group, except for body height, which showed no difference between chin-deviated and contralateral sides. In particular, ramus length presented a statistically significant difference between the two groups. CONCLUSION Based on the same degree of chin deviation in mandibular prognathism and retrusion in this study, results of right-left differences in contributing factors indicate that chin deviations are expressed easily in mandibular prognathism, whereas they occur only with significant right-left differences in relevant maxillofacial structures in individuals with mandibular retrusion.

Change of lip-line cant after 1-jaw orthognathic surgery in patients with mandibular asymmetry

INTRODUCTION The purpose of this study was to investigate the change of lip-line cant (LLC) after 1-jaw orthognathic surgery in mandibular asymmetry patients. METHODS Preoperative and postoperative data of 22 patients having 1-jaw orthognathic surgery, with menton deviation over 2 degrees before the surgery, were our subjects. LLC was measured in the preoperative and postoperative frontal photographs, and its change was correlated with various craniofacial measurements obtained from preoperative and postoperative frontal cephalograms and maxillofacial 3-dimensional computed tomography images. RESULTS Although these subjects had 2.4 degrees of LLC on average before surgery, LLC improved to 0.5 degrees after surgery, and the change (1.9 degrees ) was statistically significant. In the correlation analysis, preoperative LLC showed positive correlations with menton deviation and mandibular anterior occlusal plane cant. In the correlation analysis of LLC change, it had positive correlations with preoperative LLC and mandibular anterior occlusal plane cant and preoperative and postoperative change of menton deviation. CONCLUSIONS These results suggest that LLC is present with chin deviation, even without significant maxillary canting, and can be improved considerably by 1-jaw surgery alone.

Antibacterial effect of silver-platinum coating for orthodontic appliances

OBJECTIVE To develop a hard coating for stainless surfaces based on silver (Ag)-platinum (Pt) alloys. MATERIALS AND METHODS Ag-Pt alloys, which have high degree of biocompatibility, excellent resistance to sterilization conditions, and antibacterial properties to different bacteria, are associated with long-term antibacterial efficiency. Approximately 1.03-µm to 2.34-µm-thick coatings, as determined by scanning electron microscopy, were deposited on stainless surfaces by the simultaneous vaporization of both metals (Ag and Pt) in an inert argon atmosphere. The coating was done by physical vapor deposition. Microorganisms and eukaryotic culture cells were grown on these surfaces. RESULTS The coatings released sufficient Ag ions when immersed in phosphate-buffered saline and showed significant antimicrobial potency against Streptococcus mutans and Aggregatibacter actinomycetemcomitans strains. At the same time, human gingival fibroblast cells were not adversely affected. CONCLUSION Ag-Pt coatings on load-bearing orthodontic bracket surfaces can provide suitable antimicrobial activity during active orthodontic treatment.