• The korean journal of orthodontics
• /
• v.41 no.5
• /
• pp.324-336
• /
• 2011

Objective: The aim of this study was to conduct three-dimensional finite element analysis of individual tooth displacement and stress distribution when a posterior retraction force of 200 g was applied at different positions of the retraction hook on the transpalatal arch (TPA) of a molar, and over different lengths of the lever arm on the maxillary anterior teeth in lingual orthodontics. Methods: A three-dimensional finite element model, including the entire upper dentition, periodontal ligaments, and alveolar bones, was constructed on the basis of a sample (Nissan Dental Product, Kyoto, Japan) survey of Asian adults. Individual movement of the incisal edge and root apex was estimated along the x-, y-, and z-coordinates to analyze tooth displacement and von Mises stress distribution. Results: When the length of the lever arm was 15 mm and 20 mm, the incisal edge and root apex of the anterior teeth was displaced lingually, with a maximum lingual displacement at the lever arm length of 20 mm. When the posterior retraction hook was on the root apex, the molars showed distal displacement. When the length of the lever arm was 20 mm, anterior extrusion was reduced and the crown of the canine displaced toward the buccal side, in which case, the retraction hook was on the edge, rather than at the center, of the TPA. Conclusions: The results of the analysis showed that when 6 anterior teeth were retracted posteriorly, lateral displacement of the canine and lingual displacement of the incisal edge and root apex of the anterior teeth occur without the extrusion of the anterior segment when the length of the lever arm is longer, and the posterior retraction hook is in the midpalatal area.

• Journal of Life Science
• /
• v.33 no.10
• /
• pp.776-782
• /
• 2023

Silymarin, which is derived from dried Silybum marianum (milk thistle) seeds and fruits, possesses various beneficial properties, such as hepatoprotective, antioxidative, anti-inflammatory, and anticancer activity. This research aimed to explore the antioxidative activity of silymarin against oxidative stress and understand its molecular mechanism in RAW 264.7 cells. The study employed cell viability and reactive oxygen species (ROS) formation assays and western blot analysis. The results demonstrated that silymarin effectively reduced intracellular ROS levels induced by lipopolysaccharide (LPS) in a dose-dependent manner without causing any cytotoxic effects. Moreover, silymarin treatment significantly upregulated the expression of heme oxygenase (HO)-1, a phase II enzyme known for its potent antioxidative activity. Additionally, silymarin treatment significantly induced the expression of nuclear factor-erythroid 2 p45-related factor (Nrf) 2, a transcription factor responsible for regulating antioxidative enzymes, which was consistent with the upregulated HO-1 expression. To investigate the involvement of key signaling pathways in maintaining cellular redox homeostasis against oxidative stress, the phosphorylation status of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) was estimated by western blot analysis. The results showed that silymarin potently induced HO-1 expression, which was mediated by the phosphorylation of p38 MAPK. To further validate the antioxidative potential of silymarin-induced HO-1 expression, tert-butyl hydroperoxide (t-BHP)-induced oxidative damage was employed and attenuated by silymarin treatment, as identified by a selective inhibitor for each signaling molecule. In conclusion, silymarin robustly enhanced antioxidative activity by inducing HO-1 via the Nrf2/p38 MAPK signaling pathway in RAW 264.7 cells.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.28 no.2
• /
• pp.147-161
• /
• 2012

This study is to assess the effect of horizontal misfit of an implant supported 3-unit fixed prosthodontics on the stress development at the marginal cortical bone surrounding implant neck. Two finite element models consisting of a three unit fixed prosthodontics and an implant/bone complex were constructed on a three dimensional basis. The three unit fixed prosthodontics were designed either shorter (d=17.8mm model) or longer (d=18.0mm model) by 0.1mm than the span of two implants placed at the mandibular second premolar and second molar areas 17.9mm apart. Fitting of the fixed prosthodontics onto the implant abutments was simulated by a total of 6 steps, that is to say, 0.1mm displacement per each step, using DEFORM 3D (ver 6.1, SFTC, Columbus, OH, USA) program. Stresses in the fixed prosthodontics and implants were evaluated using von-Mises stress, maximum compressive stress, and radial stress as necessary. The d=17.8mm model assembled successfully on to the implant abutments while d=18.0mm model did not. Regardless if the fixed prosthodontics fitted onto the abutments or not, excessively higher stresses developed during the course of assembly trial and thereafter. On the marginal cortical bone around implants during the assembly, the peak tensile and compressive stresses were as high as 186.9MPa and 114.1MPa, respectively, even after the final sitting of the fixed prosthodontics (for d=17.8mm model). For this case, the area of marginal bone subject to compressive stresses above 55MPa, equivalent of the $4,000{\mu}{\varepsilon}$, i.e. the reported threshold strain to inhibit physiological remodeling of human cortical bone, extended up to 2mm away from implant during the assembly. Horizontal misfit of 0.1mm can produce excessively high stresses on the marginal cortical bone not only during the fixed prosthodontics assembly but also thereafter.

• The Journal of Korean Academy of Prosthodontics
• /
• v.47 no.2
• /
• pp.125-135
• /
• 2009

Statement of problem: Loosening or fracture of the abutment screw is one of the common problems related to the dental implant. Generally, in order to make the screw joint stable, the preload generated by tightening torque needs to be increased within the elastic limit of the screw. However, additional tensile forces can produce the plastic deformation of abutment screw when functional loads are superimposed on preload stresses, and they can elicit loosening or fracture of the abutment screw. Therefore, it is necessary to find the optimum tightening torque that maximizes a fatigue life and simultaneously offer a reasonable degree of protection against loosening. Purpose: The purpose of this study was to present the influence of tightening torque on the implant-abutment screw joint stability with the 3 dimensional finite element analysis. Material and methods: In this study, the finite element model of the implant system with external butt joint connection was designed and verified by comparison with additional theoretical and experimental results. Four different amount of tightening torques(10, 20, 30 and 40 Ncm) and the external loading(250 N, $30^{\circ}$) were applied to the model, and the equivalent stress distributions and the gap distances were calculated according to each tightening torque and the result was analyzed. Results: Within the limitation of this study, the following results were drawn; 1) There was the proportional relation between the tightening torque and the preload. 2) In case of applying only the tightening torque, the maximum stress was found at the screw neck. 3) The maximum stress was also shown at the screw neck under the external loading condition. However in case of applying 10 Ncm tightening torque, it was found at the undersurface of the screw head. 4) The joint opening was observed under the external loading in case of applying 10 Ncm and 20 Ncm of tightening torque. 5) When the tightening torque was applied at 40 Ncm, under the external loading the maximum stress exceeded the allowable stress value of the titanium alloy. Conclusion: Implant abutment screw must have a proper tightening torque that will be able to maintain joint stability of fixture and abutment.

• Journal of Oral Medicine and Pain
• /
• v.30 no.4
• /
• pp.391-400
• /
• 2005

Special Practitioner exists based on the need for special fields that are required to manage difficult patients with specialized skills distinguished from General practitioner. The purpose of dental specialist system is to manage patients who are not treatable by general practitioner by training doctors specializing in one specific field, thereby, enhancing health of the public. Oral Medicine deals with orofacial pain, oral soft tissue disease, forensic dentistry, oral diagnosis. In these days, living environments of city life bring about increase in stress which ultimately lead to increase in prevalence of temporomandibular disorder, oral soft tissue disease, neuropathies such as trigeminal neuralgia, and hence, the number of patients seeking help of those symptoms tend to increase. The purpose of this study was to analyze the rate of referrals and the routes of patients seeking help by investigating 3,707 patients who visited Department of Oral Medicine, College of Dentistry, Yonsei University, from August, 2004 to April, 2005. The results were as follows: 1. The types of disease referred to the Department of Oral Medicine were orofacial pain, oral soft tissue disease, forensic dentistry, oral diagnosis. 2. The rate of referrals was 58.51% which implies that more than half of the patients visiting the Department of Oral Medicine were referred. 3. The types of institution which made referrals were analyzed, and as a result, dental clinics made most of the referrals with the rate of 83.23%, while that from medical or oriental medical institutions was 16.78%. 4. Among the patients who visited the Department of Oral Medicine on their own, 30.52% gained the information about the Department of Oral Medicine from internet and mass media, and from neighbors. From the above results, most of the patients visiting the Department of Oral Medicine were found to be referred not only from the field of dentistry but also from the field of medicine. These suggest that Oral Medicine manages patients who are not treatable by general dental practitioners, and medical specialists tend to cooperate with the Department of Oral Medicine to manage diseases associated with Oral Medicine. Therefore, the role of Oral Medicine can be considered to be important as a special field, and the results of this study should be considered when working out a policy of Dental specialist system on demand and supply of residents in the future.

• The korean journal of orthodontics
• /
• v.31 no.3 s.86
• /
• pp.311-323
• /
• 2001

One of the various mechanics used to treat unilateral Class II malocclusion is head gear with asymmetric face bow. We made the finite element models of unilateral Class II maxillary dental arch and power arm asymmetric face bow. We designed this experiment to observe stress distribution of periodontal ligament, reaction force, and displacement and to understand force system, so to predict the therapeutic effect. On the basis of computerized tomograph of maxillary dental arch of 25 years old male with normal occlusion without extraction and orthodontic treatment history, we made finite element models of maxillary dental arch and periodontal ligament. Then we modified that model to unilateral maxillary Class II malocclusion model of which maxillary left molar displaced mesially. Also, We made finite element model of asymmetric face bow of which right outer bow shorter than left by 25mm(RMO, Penta-FormTM/Medium size, 0.045 inch iner bow, 0.072 inch outer bow). After that, retraction force of 250g, 300b, 350g were applied to maxillary first molar. We concluded as follow. 1. The Net force that both maxillary first molars were received increased as the retraction force increased. Mesially positioned tooth received more force than normally positioned tooth. But, both tooth were received distal force, so distal movement occured. 2. Both tooth received buccal lateral force. In analysis of force element, as the retraction force were increased, force of X-axis at mesially positioned tooth decreased, and force of X-axis at normally positioned tooth increased. so lateral force component moved to the side received less force from more force. 3. There were rotation, tipping with distal movement in maxillary first molar. As retraction force were increased, rotation and tipping also increased. More tipping and rotation occured at the side received more force, that is, mesially positioned tooth. Though it Is small change, displacement of same pattern occur in normally positioned tooth

• The Journal of the Korean dental association
• /
• v.52 no.12
• /
• pp.744-752
• /
• 2014

There are many causes of oral mucosal diseases, so accordingly, there are various treatments available. The most commonly used agents include adrenocortical hormones, antifungals, antivirals, antibacterials, and immunosuppressants. However, it must also be noted that improving oral hygiene and nutrition, and reducing stress are effective in symptom relief. Furthermore, patients with existing diseases of the oral mucosa should avoid behavior that may cause an increase in pain. Unfortunately, many patients are unaware of the activities that may lead to increased pain and therefore do not avoid these activities. The aim of this study was to investigate and analyze the behavior of patients with oral mucosal disease with regard to activities that led to increase pain. This cross-sectional study was performed on a sample of patients with oral mucosal disease selected from the Oral Medicine Clinic of the Pusan National Hospital during March to August 2013. These patients were randomly selected. From a total of 479 patients, 116 patients with mucosal disease were selected and 73 fully completed questionnaires were included in the analysis. Data were collected by using self-completed questionnaires. The results were as follows: Mean score of Question 13 (Not smoking) is $2.47{\pm}1.11$. Mean score of Question 11 (Not drinking alcohol or not using mouthwash containing alcohol) is $2.22{\pm}1.15$. The other questions resulted in scores lower than 1.5. The answers to the questions were scored according to the following assigned numerical values: not keeping = score of 0; little keeping = score of 1; often keeping = score of 2; always keeping = score of 3. In conclusion, patients with oral mucosal diseases unknowingly engage in activities that result in an increase in pain. Therefore, they need to be educated about how to behave to protect oral mucosal lesion.

• The Journal of the Korea Contents Association
• /
• v.12 no.11
• /
• pp.258-266
• /
• 2012

This study was conducted to investigate the differences between smokers and non-smokers' oral hygiene and college students' smoking awareness. The survey was carried out based on the 260 college students enrolled in four-year universities located in Kyungbuk, Daegu, Gangwon-do. Collected date used the SPSS 17.0 to perform the frequency and cross-analysis. 1. The daily smoking amounts of less than half pack and the smoking duration of more than 1 year and less than 3 years were to be the highest. The initiation of smoking was triggered by the curiosity and the proximal social environment. The reason of smoking was to relieve stress and habitual smoking respectively. 2. There was a significant difference between smokers and non-smokers' tooth brushing time, regular dentist visit, recent dental admission, the purpose of dental visits, scaling and oral health education. 3. There was a significant difference between smokers and non-smokers' awareness of oral hygiene in the subjective oral hygiene status. 4. There was a significant difference between smokers and non-smokers' awareness towards the impact of second-hand, after meal and one or two cigarette smoking. Based on the above results, smokers lack the awareness of smoking and oral hygiene compared to non-smokers. Therefore, the activation and the development of programs for the smoking and oral hygiene education targeting college students are considered to be necessary.

• Health Policy and Management
• /
• v.31 no.1
• /
• pp.74-90
• /
• 2021

Background: It is getting important to improve the oral health status of the elderly because oral health status may affect their health status of the whole body. In this respect, we aimed to explore the association of oral health status and behavior factors with self-rated health status by sex. Methods: Using the data from the 7th Korea National Health and Nutrition Examination Survey for health surveys and oral examinations (2016-2018), we analyzed a total of 3,070 people aged 65 or older (men: 1,329; women: 1,741). Our dependent variable, self-rated health status, was divided into two groups: not good (bad and very bad) and good (very good, good, and fair), whereas our independent variables of interest were oral health status and behavior factors. In addition to descriptive analysis and the Rao-Scott chi-square test, reflecting survey characteristics, we conducted hierarchical multivariable logistic regression analyses adjusted for socio-demographics and health status and behavior factors. All analyses were stratified by sex. Results: The proportion of people having 'not good' self-rated health was 36.5% in women but 24.5% in men. In a model adjusted for all covariates, the self-rated health status showed significant association with the self-rated oral health status. For example, in men, the risk of having 'not good' self-rated health was high in people having 'poor' (odds ratio [OR], 5.31; 95% confidence interval [CI], 2.34-12.03) self-rated oral health status and in those having 'fair' (OR, 4.03; 95% CI, 1.68-9.70) in comparison with those having 'good' self-rated oral health status. Dental status regarding speaking difficulty seemed to be very important in influencing self-rated health status. For instance, in women, compared to people having 'no discomfort' speaking difficulty, the risk of having 'not good' self-rated health was high in people having 'not bad' (OR, 1.60; 95% CI, 1.14-2.24) and 'discomfort' (OR, 1.79; 95% CI, 1.30-2.47) speaking difficulty. The covariates significantly associated with the risk of having 'not good' self-rated health were: physical activity, chronic disease, stress, and body mass index in both sexes; health insurance type and drinking only in men; and economic activity only in women. Conclusion: Oral health status and behavioral factors were associated with self-rated health status among the elderly, differently by sex. This suggests that public health policies toward better health in the elderly should take their oral health status and oral health behaviors into account in a sex-specific way.

• The Journal of Advanced Prosthodontics
• /
• v.8 no.2
• /
• pp.137-143
• /
• 2016

PURPOSE. Grinding with less stress on 3Y-TZP through proper selection of methods and instruments can lead to a long-term success of prosthesis. The purpose of this study was to compare the phase transformation and physical properties after zirconia surface grinding with 3 different grinding burs. MATERIALS AND METHODS. Forty disc-shaped zirconia specimens were fabricated. Each Ten specimens were ground with AllCeramic SuperMax (NTI, Kahla, Germany), Dura-Green DIA (Shofu Inc., Kyoto, Japan), and Dura-Green (Shofu Inc., Kyoto, Japan). Ten specimens were not ground and used as a control group. After the specimen grinding, XRD analysis, surface roughness test, FE-SEM imaging, and biaxial flexural strength test were performed. RESULTS. After surface grinding, small amount of monoclinic phase in all experimental groups was observed. The phase change was higher in specimens, which were ground with Dura-Green DIA and AllCeramic SuperMax burs. The roughness of surfaces increased in specimens, which were ground with Dura-Green DIA and AllCeramic SuperMax burs than control groups and ground with Dura-Green. All experimental groups showed lower flexural strength than control group, but there was no statistically significant difference between control group and ground with Dura-Green DIA and AllCeramic SuperMax burs. The specimens, which were ground with Dura-Green showed the lowest strength. CONCLUSION. The use of dedicated zirconia-specific grinding burs such as Dura-Green DIA and AllCeramic SuperMax burs decreases the grinding time and did not significantly affect the flexural strength of zirconia, and therefore, they may be recommended. However, a fine polishing process should be accompanied to reduce the surface roughness after grinding.