Jongrak Hong

Morphologic Evaluation and Classification of Facial Asymmetry Using 3-Dimensional Computed Tomography

PURPOSE A systematic classification is needed for the diagnosis and surgical treatment of facial asymmetry. The purposes of this study were to analyze the skeletal structures of patients with facial asymmetry and to objectively classify these patients into groups according to these structural characteristics. PATIENTS AND METHODS Patients with facial asymmetry and recent computed tomographic images from 2005 through 2009 were included in this study, which was approved by the institutional review board. Linear measurements, angles, and reference planes on 3-dimensional computed tomograms were obtained, including maxillary (upper midline deviation, maxilla canting, and arch form discrepancy) and mandibular (menton deviation, gonion to midsagittal plane, ramus height, and frontal ramus inclination) measurements. All measurements were analyzed using paired t tests with Bonferroni correction followed by K-means cluster analysis using SPSS 13.0 to determine an objective classification of facial asymmetry in the enrolled patients. Kruskal-Wallis test was performed to verify differences among clustered groups. P < .05 was considered statistically significant. RESULTS Forty-three patients (18 male, 25 female) were included in the study. They were classified into 4 groups based on cluster analysis. Their mean age was 24.3 ± 4.4 years. Group 1 included subjects (44% of patients) with asymmetry caused by a shift or lateralization of the mandibular body. Group 2 included subjects (39%) with a significant difference between the left and right ramus height with menton deviation to the short side. Group 3 included subjects (12%) with atypical asymmetry, including deviation of the menton to the short side, prominence of the angle/gonion on the larger side, and reverse maxillary canting. Group 4 included subjects (5%) with severe maxillary canting, ramus height differences, and menton deviation to the short side. CONCLUSION In this study, patients with asymmetry were classified into 4 statistically distinct groups according to their anatomic features. This diagnostic classification method will assist in treatment planning for patients with facial asymmetry and may be used to explore the etiology of these variants of facial asymmetry.

Comparative study of skeletal stability between bicortical resorbable and titanium screw fixation after sagittal split ramus osteotomy for mandibular prognathism

INTRODUCTION Resorbable screw fixation for orthognathic surgery is widely used in oral and maxillofacial surgery and has several advantages. However, surgeons are concerned about using resorbable screws in orthognathic surgery because of possible postoperative complications such as relapse, screw fracture, and infection. The purpose of this study was to evaluate the skeletal stability of bicortical resorbable screw fixation after sagittal split ramus osteotomies for mandibular prognathism. MATERIALS AND METHODS This study included 25 patients who underwent mandibular setback surgery fixed with resorbable screws after sagittal split osteotomy at the Department of Oral and Maxillofacial Surgery at Seoul National University Dental Hospital. Five resorbable screws (Inion CPS(®), Inion Ltd., Finland) were applied bicortically at each osteotomy site via a transbuccal approach. No rigid intermaxillary fixation was applied on the first postoperative day. Passive mouth opening exercises were allowed, using two light, rubber elastics for guidance. The control group was 25 patients fixed with four titanium screws. The follow-up period was 12-22 months (mean 17.8 months). Postoperative skeletal changes on lateral cephalometric radiographs were analyzed and compared between the two groups preoperatively, immediately postoperatively, and 6 months postoperatively. RESULTS The average setback was 6.9 mm and no major intraoperative complications occurred. One patient experienced infection immediately after surgery that was controlled uneventfully. The data did not demonstrate any significant difference in postoperative skeletal stability between the two groups. Differences between the immediate postoperative state and 6 months after surgery were not significant. In earlier cases, especially for patients with severe mandibular prognathism, immediate postoperative elastic traction was needed for stable occlusal guidance. CONCLUSIONS The results of this study indicate that bicortical resorbable screws offer a clinically stable outcome for the fixation of mandibular sagittal split osteotomies in mandibular prognathism. However the resorbable screws showed less stable results vertically than the titanium screws.

Quantitative biomechanical analysis of the influence of the cortical bone and implant length on primary stability.

AIM The aim of the study was to investigate the influence of cortical bone and increasing implant fixture length on primary stability. Further investigation considered the correlation between the presence of cortical bone at the marginal bone and implant stability measured by insertion torque (IT) and resonance frequency analysis (RFA), as well as implant length, were determined. MATERIALS AND METHODS Two different types of polyurethane bone models were compared. (Group 1: with cortical and cancellous bone; Group 2: with cancellous bone only). A total of 60 external type implants (∅ 4.1, OSSTEM(®), US II(®)) with different lengths (7, 10, and 13 mm) were used. IT was recorded automatically by a computer which was connected to the Implant fixture installation device during the placement. RFA was conducted to quantify the primary implant stability quotient (ISQ). All two measurements were repeated 10 times for each group. RESULTS All these differences were statistically significant between the two groups (P < 0.001) and intragroups (P < 0.001). Upon comparing the IT, cortical bone appears to have a greater influence on implant stability than implant lengths, whereas the RFA value strongly affects implant length rather than the presence of the crestal cortical bone. CONCLUSIONS The quantitative biomechanical evaluations clearly demonstrated that primary implant stability seems to be influenced by the presence of a cortical plate and total surface area of the implant fixture appears to be the decisive determinant for ISQ value.

Immediate implant placement into infected and noninfected extraction sockets: a pilot study

OBJECTIVE This study compared the osseointegration of immediate implants in dogs in infection-free sites and in sites with periradicular lesions which were removed by simulated periradicular surgery. STUDY DESIGN Periradicular surgeries were performed to remove intentionally induced periradicular lesions, followed by teeth extraction and immediate implant placement with (experimental group 1) or without (experimental group 2) membranes. In the control group, implants were placed at healthy extraction sockets. After 12 weeks, the animals were killed and the results of histomorphometric study were analyzed by Kruskal-Wallis test. RESULTS Both the control and the experimental implants were clinically acceptable. The control group showed significantly higher bone-implant contact (BIC; 76.03 +/- 7.98%) than the experimental groups 1 (59.55 +/- 14.21%) and 2 (48.62 +/- 20.22%) (P < .05). CONCLUSIONS Despite the lower BIC of the experimental groups, this pilot study showed the possibility that immediate implant placement might be successful in extraction sockets with periradicular lesions. Further studies with larger sample sizes are required.

Change of Lip Cant After Bimaxillary Orthognathic Surgery

PURPOSE The purpose of the present study was to investigate the correlations between lip cant change after bimaxillary orthognathic surgery and the ratio of lip cant change and occlusal cant change after surgery. PATIENTS AND METHODS The subjects for the present study were obtained from a group of 25 patients who underwent bimaxillary orthognathic surgery for occlusal cant correction at the Department of Oral and Maxillofacial Surgery, Samsung Medical Center (Seoul, South Korea) from January 2000 to December 2005. To be included, a patients chart had to contain a resting frontal facial photograph in the natural head position and a corresponding posteroanterior cephalogram in occlusion on the same day before surgery and postoperatively 6 months later. The lip cant change was assessed by the angle of each labial commissure and the bi-pupillary reference line. The occlusal canting change in the frontal plane was assessed with the angle between each maxillary first molar occlusal surface and the bi-frontozygomatic suture reference line. RESULTS With the angular measurement, the average occlusal cant change was 3.09 degrees (standard deviation [SD] 1.05 degrees), and the average lip cant change was 1.56 degrees (SD 1.05 degrees). With the linear measurement, the average occlusal cant change was 2.41 mm (SD 2.75), and the average lip cant change was 1.18 mm (SD 0.43). The lip cant correction ratio to occlusal cant correction was 51.5% +/- 8.4% in the angular measurement and 48.8% +/- 9.1% in the linear measurement. With Pearsons correlation analysis, the Pearson correlation coefficient was 0.869 for the angular measurement and 0.887 for the linear measurement. A high correlation was shown between the occlusal cant change and lip cant change. CONCLUSIONS Bimaxillary orthognathic surgery can correct lip cant and occlusal cant. The average amount of lip cant correction and occlusal cant correction in our study was 51.5% +/- 8.4% and 48.8% +/- 9.1%, respectively.

Correlation study between distal caries in the mandibular second molar and the eruption status of the mandibular third molar in the Korean population

OBJECTIVES The purpose of this study was to analyze the correlation parameters between the distal caries of the mandibular second molars (M2Ms) and the eruption status of the mandibular third molars (M3Ms). STUDY DESIGN The records of 786 patients who had their M3Ms extracted from 2002 to 2007 at Samsung Medical Center were reviewed. The distal caries of M2Ms, age, gender, angulations, impaction degree, and distance between M2M and M3M were assessed. RESULTS Among 883 M2Ms, 152 had distal caries (17.2%, caries group). In the caries group, 79.6% of M3Ms exhibited mesial angulation between 40 degrees and 80 degrees and 82.2% of M3Ms exhibited an impaction level in which the most coronal aspect of the M3M was located superior to the occlusal surface of the M2M. The distance between M2M and M3M (between cemontoenamel junctions) was 7-9 mm for 57.2% of the caries group. CONCLUSIONS The M3Ms under eruption status as described here could be considered for preventive extraction.

Segregation analysis of mandibular prognathism in Korean orthognathic surgery patients and their families

OBJECTIVE To investigate the existence of genetic influences on the incidence of mandibular prognathism (MP) in Korean Class III patients. MATERIALS AND METHODS The probands consisted of 100 Class III patients with MP (51 men and 49 women; mean age, 22.1 ± 5.2 years; SNA, 81.2° ± 3.2°; SNB, 84.1° ± 3.9°) who underwent orthognathic surgery. Using three-generation pedigree charts, questionnaires, and clinical examinations, general information and information regarding MP for a total of 3777 relatives of the probands (1911 men and 1866 women) was ascertained. Familial correlations of MP between possible pairs in the pedigree were estimated. Heritability (h(2)) of MP under various models was estimated. Segregation analysis was conducted under the assumption of the nonpolygenic multivariate logistic model and finite polygenic mixed model. One-, two-, and three-susceptibility-type models were evaluated. RESULTS Among 3777 relatives, 199 (97 men and 102 women) were affected with MP (5.3%). Correlation coefficients of MP incidence in full siblings and in parent-offspring were .2003 and .2036, respectively (all P < .001). The h(2) of MP was estimated as 21.5% after adjusting for sex and founder effects. Two- and three-susceptibility-type models showed that the general model fit better than the other models. MP incidence did not have a major gene transmission model and was influenced by numerous minor effect genes and their additive effects. CONCLUSION These results suggest that the inherited susceptibility to MP in Korean Class III patients might be due to the summation of minor effects from a variety of different genes and/or influence of environmental factors, rather than Mendelian transmission of major genes.

Retrospective analysis of the factors influencing mesiodentes eruption

AIM This study aimed to evaluate the factors that predict the spontaneous eruption of mesiodens. DESIGN From the records of 431 patients (346 boys and 85 girls, average age 8.8 years) who visited Samsung Medical Center from January 2002 to December 2006, 471 mesiodentes were reviewed. The eruption rate was investigated according to the width/length ratio, angulation, location, and shape determined from periapical or panoramic radiographs. RESULTS The regression model showed that the width/length ratio and angulation were important determinants influencing the eruption of mesiodentes (P < 0.001, Pearsons r = 0.619). The location of the mesiodentes also affected their eruption (P < 0.01). However, no significant relationship was detected between the shape and eruption rate of mesiodentes (P > 0.05). CONCLUSIONS A lower probability of spontaneous eruption existed when the tooth had a greater angulation, shorter length, and wider width. Spontaneous eruption occurs more often when the mesiodens is located between the permanent incisors.

Bone cement grafting increases implant primary stability in circumferential cortical bone defects

Purpose Implant beds with an insufficient amount of cortical bone or a loss of cortical bone can result in the initial instability of a dental implant. Thus, the objective of this study was to evaluate the effect of bone cement grafting on implant initial stability in areas with insufficient cortical bone. Methods Two different circumferential defect depths (2.5 mm and 5 mm) and a control (no defect) were prepared in six bovine rib bones. Fourteen implants of the same type and size (4 mm×10 mm) were placed in each group. The thickness of the cortical bone was measured for each defect. After the implant stability quotient (ISQ) values were measured three times in four different directions, bone cement was grafted to increase the primary stability of the otherwise unstable implant. After grafting, the ISQ values were measured again. Results As defect depth increased, the ISQ value decreased. In the controls, the ISQ value was 85.45±3.36 (mean±standard deviation). In circumferential 2.5-mm and 5-mm defect groups, the ISQ values were 69.42±7.06 and 57.43±6.87, respectively, before grafting. These three values were significantly different (P<0.001). After grafting the bone cement, the ISQ values significantly increased to 73.72±8.00 and 67.88±10.09 in the 2.5-mm and 5.0-mm defect groups, respectively (P<0.05 and P<0.001). The ISQ value increased to more than double that before grafting in the circumferential 5-mm defect group. The ISQ values did not significantly differ when measured in any of the four directions. Conclusions The use of bone cement remarkably increased the stability of the implant that otherwise had an insufficient level of stability at placement, which was caused by insufficient cortical bone volume. Graphical Abstract

A comparative study between data obtained from conventional lateral cephalometry and reconstructed three-dimensional computed tomography images.

Objectives The aim of this study was to verify the concordance of the measurement values when the same cephalometric analysis method was used for two-dimensional (2D) cephalometric radiography and three-dimensional computed tomography (3D CT), and to identify which 3D Frankfort horizontal (FH) plane was the most concordant with FH plane used for cephalometric radiography. Materials and Methods Reference horizontal plane was FH plane. Palatal angle and occlusal plane angle was evaluated with FH plane. Gonial angle (GA), palatal angle, upper occlusal plane angle (UOPA), mandibular plane angle (MPA), U1 to occlusal plane angle, U1 to FH plane angle, SNA and SNB were obtained on 2D cephalmetries and reconstructed 3D CT. The values measured eight angles in 2D lateral cephalometry and reconstructed 3D CT were evaluated by intraclass correlation coefficiency (ICC). It also was evaluated to identify 3D FH plane with high degree of concordance to 2D one by studying which one in four FH planes shows the highest degree of concordance with 2D FH plane. Results ICCs of MPA (0.752), UOPA (0.745), SNA (0.798) and SNB (0.869) were high. On the other hand, ICCs of gonial angle (0.583), palatal angle (0.287), U1 to occlusal plane (0.404), U1 to FH plane (0.617) were low respectively. Additionally GA and MPA acquired from 2D were bigger than those on 3D in all 20 patients included in this study. Concordance between one UOPA from 2D and four UOPAs from 3D CT were evaluated by ICC values. Results showed no significant difference among four FH planes defined on 3D CT. Conclusion FH plane that can be set on 3D CT does not have difference in concordance from FH plane on lateral cephalometry. However, it is desirable to define FH plane on 3D CT with two orbitales and one porion considering the reproduction of orbitale itself.