Topographic Analysis of the Isthmus in Mesiobuccal and Mesial Roots of First Molars in a South Korean Population

The purpose of this study was to evaluate the incidence and microscopic anatomy of the isthmus to provide more precise anatomical information about the mesiobuccal (MB) roots of the maxillary first molars and the mesial (M) roots of the mandibular first molars. Twenty-eight maxillary and 31 mandibular first molars were embedded, sectioned, stained, and observed at 30× magnification to evaluate the incidence and microscopic anatomy of the isthmus. The incidence of an isthmus 3 mm from the apex was 89.3% and 100% in the MB roots of the maxillary first molars and in the M roots of the mandibular first molars, respectively. The mean dentin thickness between the isthmus and the distal root surface was <1 mm at a distance of 3 mm from the apex in both types of roots. In this study, whenever two main canals were located in the MB roots of the maxillary first molars and in the M roots of the mandibular first molars, the likelihood of the presence of an isthmus increased. Therefore, clinicians should be aware of the thinnest dimensions in the distal surface of the MB roots of the maxillary first molars and the M roots of the mandibular first molars during nonsurgical and surgical root canal treatment.ope

Dentists' clinical decision-making about teeth with apical periodontitis using a variable-controlled survey model in South Korea

BACKGROUND: This study, by using a variable-controlled survey model, sought to compare clinical decisions made by dentists with different clinical backgrounds in South Korea regarding teeth with apical periodontitis and to identify factors that influenced decision-making. METHODS: A questionnaire with 36 questions about identical patient information, clinical signs, and symptoms was filled out by participants. Each question referred to a radiograph that had been manipulated using computer software in order to control tooth-related factors. Participants were instructed to record their demographic information and choose the ideal treatment option related to each radiograph. Simple and multivariable logistic regression analyses (p < .05) were used to investigate factors related to the decision to extract the tooth. We divided factors into dentist-related factors (gender, years of experience, and professional registration) and tooth-related factors (tooth position, coronal status, root canal filling status, and size of the periapical radiolucency). Dentists were categorized into three groups, based on professional registration: general dental practitioners (GDPs), endodontists, and other specialists. Simple logistic regression analysis (p < .05) was used to evaluate the tooth-related factors influencing extraction, depending on the dentists' specialty. RESULTS: Participants mostly preferred saving the teeth over extraction. This preference was highest among the endodontists, followed by other specialists and GDPs. Extractions were significantly preferred for molars, teeth with previous root canal fillings, and those with apical lesions greater than 5 mm. CONCLUSIONS: This study suggests that dentists' decision-making regarding teeth with apical periodontitis was associated with their work experience and specialty and influenced by tooth position, root canal filling status, and size of the apical lesion. CLINICAL RELEVANCE: This survey revealed that clinical decision-making related to teeth with apical periodontitis was affected by dentists' specialty and work experience and by tooth-related factors, such as tooth position, root canal filling status, and size of the apical lesion.ope

Deep learning for early dental caries detection in bitewing radiographs

The early detection of initial dental caries enables preventive treatment, and bitewing radiography is a good diagnostic tool for posterior initial caries. In medical imaging, the utilization of deep learning with convolutional neural networks (CNNs) to process various types of images has been actively researched, with promising performance. In this study, we developed a CNN model using a U-shaped deep CNN (U-Net) for caries detection on bitewing radiographs and investigated whether this model can improve clinicians' performance. The research complied with relevant ethical regulations. In total, 304 bitewing radiographs were used to train the CNN model and 50 radiographs for performance evaluation. The diagnostic performance of the CNN model on the total test dataset was as follows: precision, 63.29%; recall, 65.02%; and F1-score, 64.14%, showing quite accurate performance. When three dentists detected caries using the results of the CNN model as reference data, the overall diagnostic performance of all three clinicians significantly improved, as shown by an increased sensitivity ratio (D1, 85.34%; D1', 92.15%; D2, 85.86%; D2', 93.72%; D3, 69.11%; D3', 79.06%; p < 0.05). These increases were especially significant (p < 0.05) in the initial and moderate caries subgroups. The deep learning model may help clinicians to diagnose dental caries more accurately.ope

A Study on Reconditioning Procedure and Quality Requirements of DuraSpindle Exhaust Valve for Marine Two-stroke Diesel Engine

In this study, the DuraSpindle exhaust valve reconditioning of a two-stroke diesel engine was studied. In the operating vessel, the economical efficiency of the new exhaust valve spindle and the reconditioning of the existing exhaust valve has been evaluated. The reconditioned exhaust valve spindle has a low purchase price of 70%~80%, and reduced delivery time half of the new nimonic exhaust valve, which are very competitive. In order to recondition the exhaust valve spindle, it is necessary to initially check the condition of the exhaust valve spindle to evaluate whether reconditioning is possible, and additional following processes of initial machining step to remove the hardened surface, GMAW, heat treatment. There is a need for final machining and inspection steps to ensure that the spindle machined to exact dimensions. Reconditioning is only available for a company that have receiver FTA from engine maker. Initial evaluation of availability of reconditioning during initial inspection, machining, welding(GMAW), rolling, heat treatment, final machining and final inspection steps are recommended. Inconel 625 or 309L should be used as the base material for the initial processing, and grooves of the sheet surface should be coated with Inconel 718. Both GMAW and GTAW can be applied to Inconel 625 and 718 coatings. The rolling speed should be at a speed of 130m/min, a 2 ton increase in load every 30 seconds and a final load should be of 8~9 tons. Heat treatment of Inconel 718 should be initially heat up 100℃ per hour, maintain 8 hours at 720℃, 6 hours at 620℃ and initiate air cooling at 400℃ and finalize heat treatment.Maste

Pressure Root Resorption of the Second Molar Caused by Third Molar Impaction: A Case Report of Severely Resorbed Root with Vital Pulp

Pressure root resorption can be observed during the eruption of permanent dentition, especially of the maxillary canines (affecting lateral incisors) and mandibular third molars (affecting mandibular second molars). Since the cause of root resorption of the adjacent affected teeth is evident, treatment simply involves extraction of the impacted tooth. However, there have been few reports on the prognosis of the remaining resorbed tooth, as dentists often choose to extract them when damage due to root resorption is observed. We report a case involving a tooth that was severely resorbed due to pressure from an adjacent impacted tooth. After extraction of the impacted tooth, the remaining tooth retained vital pulp and survived as a functional tooth.ope

A case study on student&amp;apos;s argumentation and belief during modeling activity

우리나라 수학교육의 문제점을 극복하는 방안으로 모델링 활동이 제기 되고 그 필요성과 실제 교육현장에서 어떻게 적용될 수 있는지에 대한 연구가 있어왔다. 또한 7차 교육과정 개선 방안 연구에서는 구체적으로 다양한 교수·학습 방법으로 모델링을 활용하는 지침을 내린 바 있다. 따라서 학교 현장에서 모델링 활동을 통한 수학 학습이 현실화 되는 때가 된 것이다. 모델링 활동의 필요성 및 학습효과에 대한 연구와 모델링 학습이 어떻게 일어나는지에 대한 구체적 모델링 과정 분석 연구가 있어왔다. 따라서 현 시기 모델링 학습 과정을 기반으로 한 다양한 교육적 활동과 그 의미를 찾는 연구의 필요성이 대두되고 있는 것이다. 이러한 맥락에서 본 연구는 모델링 과정에서의 논증활동과 신념에 대해 심층적으로 이해하는 것을 목적으로 한다. 즉, 모델링 활동이 필연적으로 수반할 수밖에 없는 논증활동을 중심으로 학생들의 활동을 분석하고, 특히 그 안에서 다양하게 나타나는 학생들의 참여 역할을 확인한다. 또한 모델링 과정에서 학생의 수학 관련 신념이 어떻게 발현되는지를 살펴봄으로써 교육적 시사점을 얻고자 한다. 이에 따라 본 연구에서의 연구문제는 다음의 세 가지로 설정하였다. 1. 모델링 과정에서 학생들의 논증 활동은 어떠한 과정으로 나타내는가? 2. 모델링 과정에서 나타나는 논증활동의 참여자의 역할의 특징은 무엇인가? 3. 모델링 과정에서 나타나는 학생의 수학 관련 신념의 특징은 무엇인가? 이에 따라 본 연구는 고3 남학생 3명을 대상으로 1차시의 모델링 활동 과정을 관찰하여 논증 활동 중심으로 분석하였고, 수학 관련 신념에 대한 사전, 사후 면담을 진행하여 모델링 과정에서 어떻게 나타나는지 살펴보았다. 이때 사후면담은 학생들의 모델링 활동 과정을 담은 녹화 비디오 테잎과 면담자료를 결합할 수 있는 VBSRI(Video Based Stimulous Recall Interveiw, Prawatt, 1994) 방법을 사용하여 진행하였다. 비디오테이프 녹화는 실제로 그 당시에 중요하다고 인식된 그런 장면들을 학생들이 즉각적으로 재구성함으로써 풍부한 의미를 제공하게 된다. 면담과 비디오테이프 녹화에 대한 후속 분석은 면담할 때에는 분명하지 않았던 의미의 관계를 밝혀줄 수 있다(전영국, 2001). 첫 번째 연구문제는 실세계탐구, 상황모델개발, 수학모델개발, 일반모델개발이라는 모델링 과정에서 나타나는 논증 활동을 Toulmin의 논증 도식으로 분석하였다.두번째 연구문제는 모델링 과정에서 나타나는 논증 활동 속에서의 참여자 역할을 발화(utterence)의 내용 및 형식의 책임성(responsibility)을 기준으로 Author, Relayer, Ghostee, Spokeman인 4가지로 구분한다. 이 역할 구분을 통해 모델링 과정에서 나타나는 참여 역할을 분석하였다. 마지막으로 세 번째 연구문제는 학생들이 가지고 있는 신념이 모델링 과정에서 어떻게 나타나는지와 어떠한 변화의 징후를 보였는지를 수학관련 학생신념 사전 면담과 모델링 활동 후 사후 면담을 통해 학생별로 분석하였다. 연구 결과 다음과 같은 세 가지 결론을 내릴 수 있었다. 첫째, 학생들의 모델링 과정에서 나타나는 논증 활동을 살펴본 결과는 다음과 같다. 우선 모델링 활동을 이끄는 주요한 핵심 활동에서 논증 활동이 필연적으로 수반되었고, 실세계 탐구, 상황모델 개발, 수학모델 개발, 일반모델 개발이라는 모델링 과정이 진행되면서 이전 단계의 논증의 결과물을 다시 새로운 단계의 자료로써 사용하는 논증의 연쇄가 나타남을 확인할 수 있었다. 둘째, 모델링 과정에서 학생들은 다양한 역할을 수행하면서 논증 활동에 참여했다. 셋째, 모델링 과정을 통해 학생들의 수학 관련 신념에서 변화의 징후를 발견할 수 있다. 본 연구의 분석 결과는 실제 교육현장에서의 모델링 수업에서의 논증 활동에서 교사를 포함한 참여 역할에 대한 후속 연구에 길잡이 역할을 함과 동시에 학습 과정에서의 학생들의 신념이 어떠한 의미를 가지는지를 보여주는 사례연구로서 교육적 시사점을 제공한다.;Modeling activities involve argumentation and students&amp;apos; belief influence their practices in modeling process. This study investigates student&amp;apos;s argumentation and belief during modeling activity. According to the purpose of this research, the following three research questions were proposed. First, what process is showed argumentation which students conduct during modeling activity? Second, what are characteristics of participant&amp;apos;s role during modeling activities? Third, what are characteristics of students&amp;apos; mathematics related belief during modeling activities? This The research design consisted of one modeling activity with three twelve-grade students. All of students&amp;apos; practice during modeling activity were videotaped and qualitive evidence from pre-post interviews were collected. As based in the case study, the research questions were analyzed in depth. First, key activities which lead modeling process involved argumentations. During modeling activity, we could see argument chain in which argumentation conclusion of the preceding step was used as data of new next step. Second, we saw different participant role in argumentation during modeling activity. Third, students&amp;apos; mathematical related belief reflected on modeling process, and we could see symptoms of change in students&amp;apos; belief during modeling activity. This study makes suggestion on participant role of teacher and factor changing students&amp;apos; belief in modeling lesson of actual mathematic classroom.Ⅰ. 서론 = 1 A. 연구의 필요성 및 목적 = 1 B. 연구문제 = 3 Ⅱ. 이론적 배경 = 4 A. 모델링 활동과 논증 활동 = 4 1. 논증 활동(argumentation)의 의미 = 4 2. 모델링 과정에서 논증 활동 = 6 3. Toulmin의 논증 도식 = 8 B. 학생의 수학 관련 신념 = 13 1. 신념의 의미 = 13 2. 학생의 수학 관련 신념의 개념틀 = 16 3. 모델링 과정에서의 신념 = 20 Ⅲ. 연구 방법 및 절차 = 23 A. 연구 대상 = 23 B. 연구 절차 = 25 C. 모델링 활동 과제 = 27 D. 자료 수집 및 분석 방법 = 30 1. 자료 수집 = 30 2. 모델링 활동 관찰 = 30 3. 사후 면담 = 31 4. 자료의 분석 = 32 5. 타당성과 신뢰도 = 33 6. 연구의 제한점 = 34 Ⅳ. 연구 결과 = 35 A. 모델링 과정에서의 논증활동 = 35 1. 실세계 탐구 과정 = 36 2. 상황모델 개발 과정 = 41 3. 수학모델 개발 과정 = 46 B. 논증 활동에서의 참여 역할 = 50 C. 모델링 과정에서의 학생 신념 = 55 1. 연구 대상자들의 수학 관련 신념 = 55 2. 모델링 과정에서 나타난 학생의 신념의 특징 = 61 Ⅴ. 결론 및 제언 = 64 참고 문헌 = 66 부록 = 70 ABSTRACT = 8

불소 농도에 따른 합성 수산화인회석의 결정 성장에 대한 정성 분석

Fluorides are known to be a significant factor that promote remineralization and stabilize hydroxyapatite crystals within the enamel. In spite of many studies about the effect of fluoride on remineralization of tooth enamel, its mechanism has not yet been established. This study was designed to examine the effect of fluoride concentration on crystal growth of synthetic hydroxyapatite (HA) particles in pH 7.0 supersaturated solutions with different fluoride concentrations (0, 1, 2, 4, 8, 16, 32 and 64 ppm) by means of FE-SEM, FE-TEM, x-ray diffraction (XRD) and FT-IR. Eight groups of pH 7.0 calcium phosphate supersaturated solutions were prepared with different fluoride concentrations (0, 1, 2, 4, 8, 16, 32 and 64 ppm). Each solution was introduced into the reactive column containing the synthetic HA (Sigma Aldrich) by using a peristaltic pump for constant reaction rate (2.5 mL/h) for 48 hours. Calcium phosphates precipitated on the synthetic HA surface while solutions flew through the reactive column. The resulting products were prepared for FE-SEM and FE-TEM to evaluate the morphological changes on the crystals and examined by XRD and FT-IR to identify the crystals. The FE-SEM examination revealed various morphological changes of the crystals, where the size and the number of new crystals on the surface of the seed HA increased as the fluoride concentration was raised, with additional less-ordered crystallites at relatively high concentrations of fluorides. FE-TEM examination showed an additional amorphous layer on the surface of the crystals with the existence of fluoride, whereas definite lattice structures completely reached the surface of the crystals without fluorides. XRD data showed that all crystals had the same patterns as the unreacted synthetic HA, regardless of fluoride concentration. With FT-IR results, the intensity of the OH-libration mode decreased when adding fluoride, compared to that of pristine HA. This study found that fluorides had an effect on crystal growth of the synthetic hydroxyapatite, depending on the concentration of the fluorides. The introduction of fluoride promotes the growth of HA, resulting in crystal growth on the surface of seed HA at relatively low concentrations of fluoride and additional less-ordered HA crystallites at relatively high concentrations of fluoride. The resulting crystals were considered to be partially fluoridated HA under room temperature and pH 7.0 supersaturated solutions, regardless of the concentration of the fluoride. Under the experimental conditions in this study, fluorides mainly react with the surface of the seed HA and have impact on the growth of HA in a less effective manner as the concentration of fluoride increases.open박