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Agency Costs and Equity Mispricing
박정철,Christos Pantzalis 한국증권학회 2014 Asia-Pacific Journal of Financial Studies Vol.43 No.1
We investigate a link between agency costs and equity mispricing. We employ comprehensive,multi-dimensional measures of agency costs and mispricing, and find that mispricing is significantlyand positively related to agency costs. We also explore the effect of equity-basedcompensation on the impact of agency costs on mispricing. Our investigation extends previousstudies that do not separately account for the options and restricted stock grants componentsof equity-based compensation. We show that stock options, originally intended toresolve conflicts of interest, exaggerate the problem and this phenomenon is pronouncedespecially when firms are overvalued. Overall, our results imply that compensation packagesthat are not structured optimally could lead to greater mispricing.
박정철,임현창,Joo-Yeon Sohn,Jeong-Ho Yun,Ui-Won Jung,김창성,조규성,김종관,최성호 대한치주과학회 2009 Journal of Periodontal & Implant Science Vol.39 No.2
Purpose: Synthetic bone products such as biphasic calcium phosphate (BCP) are mixtures of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP). In periodontal therapies and implant treatments, BCP provides to be a good bone reconstructive material since it has a similar chemical composition to biological bone apatites. The purpose of this study was to compare bone regeneration capacity of two commercially available BCP. Methods: Calvarial defects were prepared in sixteen 9-20 months old New Zealand White male rabbits. BCP with HA and β-TCP (70:30) and BCP with Silicon-substituted hydroxyapatite (Si-HA) and β-TCP (60:40) particles were filled in each defect. Control defects were filled with only blood clots. Animals were sacrificed at 4 and 8 week postoperatively. Histomorphometric analysis was performed. Results: BCP with HAand β-TCP 8 weeks group and BCP with Si-HA and β-TCP 4 and 8 weeks groups showed statistically significant in crease (P <0.05) in augmented area than control group. Newly formed bone area after 4 and 8 weeks was similar among all the groups. Residual materials were slightly more evident in BCP with HA and β-TCP 8 weeks group. Conclusions: Based on histological results, BCP with HA and β-TCP and BCP with Si-HA and β-TCP appears to demonstrate acceptable space maintaining capacity and elicit significant new bone formation when compared to natural bone healing in 4 and 8 week periods.
박정철,양기빈,최연아,김용태,정의원,김창성,조규성,채중규,김종관,최성호 대한치주과학회 2010 Journal of Periodontal & Implant Science Vol.40 No.4
Purpose: There is no consensus regarding the relationship between the width of keratinized mucosa and the health of periimplant tissues, but clinicians prefer to provide enough keratinized mucosa around dental implants for long-term implant maintenance. An apically positioned flap during second stage implant surgery is the chosen method of widening the keratinized zone in simple procedures. However, the routine suture techniques used with this method tend to apply tension over the provisional abutments and decrease pre-existing keratinized mucosa. To overcome this shortcoming, a pre-fabricated implant-retained stent was designed to apply vertical pressure on the labial flap and stabilize it in a bucco-apical direction to create a wide keratinized mucous zone. Methods: During second stage implant surgery, an apically displaced, partial thickness flap with a lingualized incision was retracted. A pre-fabricated stent was clipped over the abutments after connecting to the provisional abutment. Vertical pressure was applied to displace the labial flap. No suture was required and the stent was removed after 10 days. Results: A clinically relevant amount of keratinized mucosa was achieved around the dental implants. Buccally displaced keratinized mucosa was firmly attached to the underlying periosteum. A slight shrinkage of the keratinized zone was noted after the healing period in one patient, but no discomfort during oral hygiene was reported. Clinically healthy gingiva with enough keratinized mucosa was achieved in both patients. Conclusions: The proposed technique is a simple and time-effective technique for preserving and providing keratinized tissue around dental implants
박정철,Yoo-Jung Um,Ui-Won Jung,김창성,최성호,김종관 대한치주과학회 2010 Journal of Periodontal & Implant Science Vol.40 No.1
Purpose: Periodontal regenerative therapies for defects created by severe periodontitis are mainly focused on bone regeneration. Although cementum regeneration needs to be better understood, it is believed to play an important role in periodontal regeneration. The first step toward a full understanding of cementum regeneration is to compare repaired cementum to pristine cementum. This study, which used histological techniques, was designed to focus on cementum regeneration and to compare pristine cementum to repaired cementum after surgical procedures with 8 and 24 week healing periods in a canine model. Methods: Buccal and lingual mucoperiosteal flaps of 10 beagle dogs were surgically reflected to create critical-sized defects. Intrabony one-wall defects, of which dimension is 4 mm width and 5 mm depth, were made at the distal aspect of mandibular second premolars and the mesial aspect of mandibular fourth premolars in the right and left jaw quadrants. Animals were sacrificed after 8 and 24 weeks post-surgery for histological specimen preparation and histometric analysis. Results: The repaired cem entum was composed mostly of acellular cementum and cellular mixed fiber cementum and was thicker in the apical area than in the coronal area. The acellular cementum of the supracrestal area appeared to be amorphous. The newly formed cellular cementum was partially detached from the underlying circumpulpal dentin, which implied a weak attachment between new cementum and dentin, and this split was observed to a lesser extent in the 24 week group than in the 8 week group. The vertical height of the repaired cementum was greater in the 24 week group than in the 8 week group. Conclusions: Within the limitations of this study, we can conclude that repaired cementum after root planing was mainly acellular cementum and cementum tissue that matured to a shape similar to pristine cementum as the healing progressed from 8 to 24 weeks.
박정철,최성호,김영태,김선종,강희정,이정호,신승철,차영주 대한치주과학회 2011 Journal of Periodontal & Implant Science Vol.41 No.1
Purpose: Infection with human immunodeficiency virus (HIV) remains a major global threat, and although the prevalence is comparatively still very low, the number of HIV-positive Koreans is increasing. However, there are no official guidelines as to how to treat people living with HIV/acquired immunodeficiency syndrome (AIDS) (PLWHA) or how to screen for potentially infectious people. This study assessed the level of knowledge and attitudes of dentists in Korea toward PLWHA, and their attitudes to screening patients for HIV infections. Methods: A cross-sectional prospective survey targeting dentists working in Korea was conducted using a self-administered questionnaire. Results: A satisfactory level of knowledge about HIV/AIDS and a relatively positive attitude toward PLWHA was found. Most of the respondents preferred rapid HIV testing using oral fluid as a specimen. The general attitude of dentists toward HIV/AIDS is sufficiently positive to enable provision of the best treatment to the patients in need. Conclusions: Most of the dentists require HIV testing in dental clinics. In spite of their needs, there are several obstacles. It is hoped that financial considerations and official legal requirements related to HIV testing strategies will be considered.
Bisphosphonates induced osteonecrosis of the jaw의 기전, 예방, 위험 평가 및 치료 방법
박정철,정의원,김창성,조규성,채중규,김종관,최성호,Park, Jung-Chul,Jung, Ui-Won,Kim, Chang-Sung,Cho, Kyoo-Sung,Chai, Jung-Kiu,Kim, Chong-Kwan,Choi, Seong-Ho 대한치주과학회 2009 Journal of Periodontal & Implant Science Vol.39 No.1
Purpose: Bisphosphonates are drugs used to suppress osteoclastic activity and to treat osteoporosis, Paget's disease of bone and bone metastasis. The purpose of this report is to review the literatures on bisphosphonates use that could affect bone healing and cause osteonecrosis of the jaws. Materials and methods: Medline research was carried out to find relevant articles on bisphosphonates and osteonecrosis of the jaw. Results: Oral administration of bisphosphonates is reported to decrease the risk of adverse bone outcomes. On the contrary, IV bisphosphonates is known to significantly increase the risk. Prevention of the osteonecrosis of the jaw is primary concern before usage. If the adverse bone reaction takes place, proper management and treatments are required to alleviate pain of patients and prevent further progression of necrosis. Conclusion: Case reports of bisphosphonates induced osteonecrosis of the jaw are increasing. Dentists and physicians should be aware of the higher frequency of osteonecrosis of the jaw in patients receiving IV bisphosphonates and be prepared to prevent and cope with adverse bone reaction.
박정철,추순남,권정렬,이헌용,Park, Jung-Cheul,Chu, Soon-Nam,Kwon, Jung-Youl,Lee, Heon-Yong 한국전기전자재료학회 2008 전기전자재료학회논문지 Vol.21 No.1
To study the effects of $H_2$ gas on AIN insulation thin film, we prepared AIN thin film on Si and GaAs substrate by means of reactive sputtering method using $H_2$ gas as an additives, With treatment conditions of $H_2$ gas AIN thin film shows variable electrical properties such as its crystallization and hysterisis affected to electrical property, As a results, AIN thin film fabricated on Si substrate post-treated with $H_2$ gas for 20 minutes shows much better an insulation property than that of pre-treated, And AIN film treated with $H_2$ gas comparing to non-treated AIN film shows a flat band voltage decreasment. But In GaAs substrate $H_2$ gas does not effect on the flat band voltage.