• Journal of the Korean Academy of Esthetic Dentistry
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• v.27 no.2
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• pp.75-81
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• 2018

The aim of this study was to evaluate the biomechanical behavior and long-term safety of high performance polymer PEKK as an intraradicular dental post-core material through comparative finite element analysis (FEA) with other conventional post-core materials. A 3D FEA model of a maxillary central incisor was constructed. A cyclic loading force of 50 N was applied at an angle of $45^{\circ}$ to the longitudinal axis of the tooth at the palatal surface of the crown. For comparison with traditionally used post-core materials, three materials (gold, fiberglass, and PEKK) were simulated to determine their post-core properties. PEKK, with a lower elastic modulus than root dentin, showed comparably high failure resistance and a more favorable stress distribution than conventional post-core material. However, the PEKK post-core system showed a higher probability of debonding and crown failure under long-term cyclic loading than the metal or fiberglass post-core systems.

• The korean journal of orthodontics
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• v.51 no.1
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• pp.32-42
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• 2021

Objective: To investigate the three-dimensional forces created by clear aligners on mandibular teeth during differential activation with en-masse retraction and/or intrusion in vitro. Methods: Six sets of clear aligners were designed for differential en-masse retraction and/or intrusion procedures in a first premolar extraction model. Group A0 was a control group with no activation. Groups A1-5 underwent different degrees of retractions and/or intrusions. Each group consisted of 10 aligners. Aligner forces were measured on a multi-axis force/torque transducer measurement system in real-time. Results: In the en-masse retraction groups (A1 and A2), lingual and extrusive forces were observed on the incisors; the canines mainly received distal forces; intrusive forces were seen on the second premolars; and the molars received mesial forces. In the en-masse retraction and intrusion groups (A3, A4, and A5), incisors also received lingual and extrusive forces; canines received distal and intrusive forces; mesial and extrusive forces were seen on the second premolars; and the second molars received distal and intrusive forces. The vertical forces on the incisors did not differ significantly among groups A1, A3, and A5. However, the vertical forces on the second premolars reversed from intrusion in group A1 to extrusion in groups A3 and A5. Conclusions: With clear aligners, the "bowing effect" is seen during en-masse anterior teeth retraction and can be partially relieved by performing en-masse retraction accompanied by anterior teeth intrusion. Vertical control of incisors remained unsolved during en-masse retraction, even when intrusive activation was added to the anterior teeth.

• Journal of Drive and Control
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• v.17 no.4
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• pp.141-151
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• 2020

The aim of this study was to analyze the safety factor of range-shift gear pairs on multi-purpose agricultural implement machinery for an optimal design of a transmission system. Gear-strengths such as bending and contact stress and safety factors were analyzed under three load conditions: an equivalent engine torque at plow tillage, a rated engine torque, and the maximum engine torque. Root and contact safety factor were calculated to be 3.88, 5.14, 2.24, 2.11, 2.21, 0.99 and 0.78, 0.94, 0.65, 0.68, 0.84, 0.85, respectively, under equivalent engine torque condition at the plow tillage. The root and contact safety factor were calculated to be 1.91, 2.53, 1.10, 1.04, 1.07, 0.48 and 0.55, 0.66, 0.46, 0.48, 0.59, 0.59, respectively, under rated engine torque condition. The root and contact safety factor were calculated to be 1.60, 2.11, 0.92, 0.87, 0.90, 0.40 and 0.51, 0.61, 0.42, 0.44, 0.54, 0.54, respectively, under the maximum engine torque condition. The multi-purpose agricultural implement machinery could be conducted under plow tillage operation. However, gear specifications for tooth surface need modification because the gear surface would be broken at all driving conditions as safety factors are lower than 1.

• The Journal of the Korea Contents Association
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• v.21 no.5
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• pp.996-1003
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• 2021

The purpose of this study is to evaluate the reliability of repeated measurements of several dental scanners. Blue-lighted scanners, white-light scanners and optical-type scanners are used in the study of repeatability in this study. The measurement results were calculated as root mean square (RMS) and the significance level was confirmed by applying the 1-way ANOVA statistical technique (𝛼=.05). According to the statistical analysis, the scanner with the largest RMS value was Z-opt group (38.2 ㎛. Next, D-white was 35.2 ㎛ and the group with the lowest RMS value was I-blue (34.1 ㎛). The comparison of RMS means between each group was not significant (p>.05). From this result, the blue light had the lowest error in repeatability of dental scanners, but no statistical significance. The conclusion of this study is that the study results are clinically acceptable.

• The Journal of the Korea Contents Association
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• v.21 no.8
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• pp.258-270
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• 2021

This study aimed to investigate the effects of the virtual reality simulation for malocclusion examination for dental education. A 4-step modeling procedure was applied to develop a tooth model with a realistic level in order to be held and observed in detail. Eighty-six participants used HMDs to examine the developed virtual dental simulation to identify their perception according to expertise levels. The independent variable, expertise group, included three levels: 29 juniors, 29 seniors, and 28 dentists, respectively. The dependent variables, that were task-load and usability, were measured through two cases. Results showed that the junior group perceived a higher level of mental demands and embarrassment than the dentist group. It indicated that the perceived task load varies according to the expertise levels in the simulation task. However, the senior group perceived a higher level of ease of use than the dentist group. This study presented the implications for the development of virtual reality simulation in detail.

• Journal of Dental Anesthesia and Pain Medicine
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• v.22 no.1
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• pp.1-10
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• 2022

Background: Inferior alveolar nerve block (IANB) is known to have a lower success rate for anesthesia in patients with irreversible pulpitis. This calls for supplementary techniques to effectively anesthetize such patients. This systematic review aimed to evaluate the published literature for determining the success rate of anesthesia induction using post-IANB intraligamentary (IL) injection in the mandibular teeth of patients with symptomatic irreversible pulpitis. The review question was, "What is the success rate of IL injection in the mandibular teeth of patients with irreversible pulpitis as a supplementary technique for endodontic treatment?" Methods: A thorough search of electronic databases and manual searches were performed. The protocol of the review was framed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist and was registered in the International Prospective Register of Ongoing Systematic Reviews (PROSPERO) with a proper criterion for inclusion and exclusion of studies. The included studies were analyzed using the Cochrane Collaboration "Risk of Bias" tool. A meta-analysis that included a comparison of primary nerve block and supplemental IL injection was performed. The success rate was evaluated using the combined risk ratio (RR) with a random risk model. A funnel plot was created to measure publication bias. Results: After all analyses, four studies were included. In the forest plot representation, RRs were 3.56 (95% CI: 2.86, 4.44), which were in favor of the supplemental IL injections. Statistical heterogeneity was found to be 0%. These values suggest that supplemental IL injections provide better success rates for anesthesia. Conclusion: According to the pooled qualitative and quantitative analyses, supplemental IL injections increased anesthetic efficacy.

• Journal of the Korean Wood Science and Technology
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• v.31 no.5
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• pp.96-103
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• 2003

This study was conducted to evaluate the tensile properties of metal plate connector for the domestic major softwoods, such as Korean red pine, Korean white pine, and Japanese larch. The maximum tensile load of Korean red pine was 3,612kgf in AA type, it was 1.2 and 1.7 times higher load than that of Japanese larch and Korean white pine. In EA type, it was 2,704kgf, and 1.1 and 1.5 times higher than the loads of Japanese larch and Korean white pine. The failure modes of metal plate connector were metal plate withdrawal, plate tensile failure, and wood shear block failure. The failure mode of Korean red pine connector was tensile failure of plate, that is reason of the high tensile load resistance for metal plate connections in Korean red pine. The mechanical properties of metal plate connector could be predicted by the Foschi model parameter. In the initial stage, the Korean red pine connector was stiffer than the other species. The design values for metal plate connector per tooth was 25, 22, and 15kgf for Korean red pine, Japanese larch, and Korean white pine in AA type and 19, 17, and 13kgf in EA type.

• The Korean Journal of Pain
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• v.35 no.4
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• pp.383-390
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• 2022

Background: The treatment of trigeminal neuralgia remains a challenging issue. Stem cells from human exfoliated deciduous teeth (SHED) provide optimized therapy for chronic pain. This study aimed to investigate the mechanisms underlying the attenuation of trigeminal neuralgia by SHED. Methods: Trigeminal neuralgia was induced by chronic constriction injury of the infraorbital nerve. The mechanical threshold was assessed after model establishment and local SHED transplantation. Endoplasmic reticulum (ER) morphology and Caspase12 expression in trigeminal ganglion (TG) was evaluated as well. BiP expression was observed in PC12 cells induced by tunicamycin. Results: The local transplantation of SHED could relieve trigeminal neuralgia in rats. Further, transmission electron microscopy revealed swelling of the ER in rats with trigeminal neuralgia. Moreover, SHED inhibited the tunicamycin-induced up-regulated expression of BiP mRNA and protein in vitro. Additionally, SHED decreased the up-regulated expression of Caspase12 mRNA and protein in the TG of rats caused by trigeminal neuralgia after chronic constriction injury of the infraorbital nerve mode. Conclusions: This findings demonstrated that SHED could alleviate pain by relieving ER stress which provide potential basic evidence for clinical pain treatment.

• The korean journal of orthodontics
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• v.53 no.6
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• pp.374-392
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• 2023

Objective: Assess and evaluate the different indicators of oral health-related quality of life (OHRQoL) among patients treated with clear aligners (CAs) versus those treated with conventional fixed orthodontics (FAs). Methods: An electronic search was performed on the database is Web of Science, Scopus, and Embase databases. Randomized and non-randomized control trials, cross-sectional, prospective cohort and retrospective trials were included. Quality was assessed with risk of bias tool and risk of bias in non-randomised studies. Meta-analyses were performed with random effects models, estimating the standardized and non-standardized mean differences, odds ratio and risk ratio as the measure of effect. The effect on time was determined using a meta-regression model. Results: Thirty one articles were included in the qualitative synthesis and 17 in the meta-analysis. CAs had a significantly lower negative impact on QoL, with an "important" effect size, while the influence of time was not significant. Periodontal indicators plaque index (PI), gingival index (GI), probing depth (PD), and bleeding on probing show significantly better values in patients treated with CAs, with moderate to large effect sizes. PI and GI have a significant tendency to improve over time. In microbiological indicators, CAs present a lower biofilm mass without differences in the percentage of patients with high counts of Streptococcus mutans and Lactobacilli bacteria. The risk of white spot lesion onset is ten times lower in carriers of CAs. Conclusions: Patients wearing CAs show better periodontal indicators, less risk of white spot development, less biofilm mass and a better QoL than patients with FAs.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.46 no.3
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• pp.1-6
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• 2023

In the realm of dental prosthesis fabrication, obtaining accurate impressions has historically been a challenging and inefficient process, often hindered by hygiene concerns and patient discomfort. Addressing these limitations, Company D recently introduced a cutting-edge solution by harnessing the potential of intraoral scan images to create 3D dental models. However, the complexity of these scan images, encompassing not only teeth and gums but also the palate, tongue, and other structures, posed a new set of challenges. In response, we propose a sophisticated real-time image segmentation algorithm that selectively extracts pertinent data, specifically focusing on teeth and gums, from oral scan images obtained through Company D's oral scanner for 3D model generation. A key challenge we tackled was the detection of the intricate molar regions, common in dental imaging, which we effectively addressed through intelligent data augmentation for enhanced training. By placing significant emphasis on both accuracy and speed, critical factors for real-time intraoral scanning, our proposed algorithm demonstrated exceptional performance, boasting an impressive accuracy rate of 0.91 and an unrivaled FPS of 92.4. Compared to existing algorithms, our solution exhibited superior outcomes when integrated into Company D's oral scanner. This algorithm is scheduled for deployment and commercialization within Company D's intraoral scanner.