Heon-Jin Park

Method to classify dental arch forms

INTRODUCTION The aim of this study was to propose a method to classify dental arch forms of subjects with normal occlusion into several types that can ensure both goodness of fit and clinical application. METHODS We selected 306 subjects with normal occlusion from 15,836 young adults, recorded 14 reference points that defined the distance between 2 arch forms as the area between 2 arches, and then classified the dental arch forms by using the partitioning around medoids clustering and silhouette method. We measured tooth size, arch width, basal arch width, arch depth, mesiodistal angulations, and buccolingual inclinations. RESULTS We identified 3 types of arch forms, and cross-classification of the maxillary by mandibular arch forms showed a more frequent distribution in the diagonal elements than in the off-diagonal elements. The 3 arch forms showed differences in tooth size, arch width, basal arch width, and inclination of the posterior teeth. CONCLUSIONS By defining area discrepancies as distance measures and applying them to the cluster method by using medoids, the dental arch form can be classified keeping control for the extremes without bias. It is hoped that this method will have possible clinical applications in determining the shape and number of preformed orthodontic arch forms.

Variation of the intermaxillary tooth-size relationship in normal occlusion

The purpose of this study was to explore the intermaxillary tooth-size relationship that is attributed to normal occlusion using multivariate cluster analysis, while simultaneously incorporating the full dentition as a data set. From the central incisor to the second molar, the tooth sizes of 307 subjects (188 males and 119 females; mean age ± standard deviation, 19.9 ± 3.3 years) with normal occlusion were investigated. Tooth-size data were analysed separately for the maxilla and the mandible. When clustering, the partitioning around medoids (PAM) algorithm was performed with the transformed data based on principal component analysis (PCA). After the subjects were classified into four groups, the cluster memberships were cross-classified, and the distribution pattern and intermaxillary tooth-size relationships were explored. Bolton tooth ratio showed a relatively wide range, and this was indicative of the variability in tooth size in subjects with a normal occlusion. However, the patterns of the intermaxillary tooth-size relationship were similar for males and females, and this result was concordant with the findings of the classic Bolton analysis. Using the multivariate approach to analyse the tooth-size data set of an individual patient and then comparing the results with the normal occlusion cluster has possible clinical applications in determining the amount and location of tooth-size control in orthodontics.

Synergistic effect of ionizing radiation and beta-Lapachone against RKO human colon adenocarcinoma cells.

PURPOSE To reveal the interaction between beta-Lapachone (beta-lap) and ionizing radiation in causing cell death in RKO human colon adenocarcinoma cells, and to elucidate the potential usefulness of combined beta-lap treatment and radiotherapy for cancer treatment. MATERIALS AND METHODS The cytotoxicities of various treatments were determined in vitro using clonogenic and apoptotic cell death. The changes in cell cycle distribution were studied using flow cytometry and an in vitro kinase assay. The tumor growth was studied using RKO tumors grown s.c. in the hind leg BALB/c- nuslc nude mice. RESULTS beta-Lap caused clonogenic cell death and rapid apoptosis in RKO cells in vitro, in a dose dependent manner. The repair of sublethal radiation damage was almost completely inhibited when cells were maintained in beta-lap during the interval between the two-dose irradiation. Flow cytometry study demonstrated that beta-lap induced apoptosis, independent of the cell cycle phase, and completely prohibited the induction of radiation-induced G2 arrest in irradiated cells. The prohibition of radiation-induced G2 arrest is unclear, but may be related to the profound suppression of the p53, p21 and cyclin B1-Cdc2 kinase activities observed in cells treated with beta-lap. The combination of beta-lap and radiation markedly enhanced the radiation-induced growth suppression of tumors. CONCLUSION beta-Lap is cytotoxic against RKO cells, both in vitro and in vivo, and also sensitized cells to ionizing radiation by inhibiting sublethal radiation damage repair. beta-lap is potentially useful as a potent anti-cancer chemotherapy drug and potent radiosensitizer against cancer cells.

Development of Peer-Group-Classification Criteria for the Comparison of Cost Efficiency among General Hospitals under the Korean NHI Program

OBJECTIVES To classify general hospitals into homogeneous systematic-risk groups in order to compare cost efficiency and propose peer-group-classification criteria. DATA SOURCES Health care institution registration data and inpatient-episode-based claims data submitted by the Korea National Health Insurance system to the Health Insurance Review and Assessment Service from July 2007 to December 2009. STUDY DESIGN Cluster analysis was performed to classify general hospitals into peer groups based on similarities in hospital characteristics, case mix complexity, and service-distribution characteristics. Classification criteria reflecting clustering were developed. To test whether the new peer groups better adjusted for differences in systematic risks among peer groups, we compared the R(2) statistics of the current and proposed peer groups according to total variations in medical costs per episode and case mix indices influencing the cost efficiency. DATA COLLECTION A total of 1,236,471 inpatient episodes were constructed for 222 general hospitals in 2008. PRINCIPAL FINDINGS New criteria were developed to classify general hospitals into three peer groups (large general hospitals, small and medium general hospitals treating severe cases, and small and medium general hospitals) according to size and case mix index. CONCLUSIONS This study provides information about using peer grouping to enhance fairness in the performance assessment of health care providers.

Bootstrap method to evaluate tightness of clusters with application to the Korean standard occlusion study

Dental arch form is an important part of dental orthodontic practice. Distance-based clustering methods are often used to find standard arch forms. In particular, S-J. Lee, S.I. Lee, J. Lim, H-J. Park, and T. Wheeler Method to classify human dental arch form, Am. J. Orthod. Dentofacial Orthop. (2010), to appear] propose a 1-type distance which is invariant to the location-shift and the rotational transformation. Despite the popularity of the distance-based methods, little attention is given to the choice of the distance which has a great influence on final clusters. We have three goals in this paper. First, we study the properties of the 1-type distance by Lee et al. (2010). Second, we propose a bootstrap-based procedure to evaluate quantitatively how good the clusters are. Finally, we apply the bootstrap procedure to the Korean standard occlusion study and compare the existing distance-based clustering methods in previous literature.