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

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

Effect of thickness on the translucency of resin-based composites and glass-ceramics

This study was aimed to evaluate the effect of thickness (1, 2, 3, and 4 mm) on the translucency of resin-based composites (RBCs) and glass-ceramics, and compare the influence of the thickness of those materials on the translucency parameter (TP) value. The materials were divided into two groups, eight RBCs in Group 1 and five glass-ceramics in Group 2 and TP, ΔL*, Δa*, and Δb* were compared. Statistically significant differences were present in the 2, 3, and 4 mm in the TP, in the 2 and 4 mm in ΔL*, and in all thicknesses in Δa* and Δb* betweent the two groups. The TP of RBCs and glass-ceramics decreased as thickness increased, especially from 1 mm to 2 mm. The TP values of the RBCs were more significantly decreased as the thickness of the material increased from 2 mm to 4 mm than those of the glass-ceramics. © 2023, Japanese Society for Dental Materials and Devices. All rights reserved.ope