• Restorative Dentistry and Endodontics
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• 제46권4호
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• pp.56.1-56.11
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• 2021

Objectives: This study evaluated 2 nickel-titanium rotary systems and a complementary protocol with an ultrasonic tip and a small-diameter instrument in flattened root canals. Materials and Methods: Thirty-two human maxillary second premolars with flattened canals (buccolingual diameter ≥4 times larger than the mesiodistal diameter) at 9 mm from the radiographic apex were selected. The root canals were prepared by ProDesign Logic (PDL) 30/0.01 and 30/0.05 or Hyflex EDM (HEDM) 10/0.05 and 25/0.08 (n = 16), followed by application of the Flatsonic ultrasonic tip in the cervical and middle thirds and a PDL 25/0.03 file in the apical third (FPDL). The teeth were scanned using micro-computed tomography before and after the procedures. The percentage of volume increase, debris, and uninstrumented surface area were analyzed using the Kruskal-Wallis, Dunn, Wilcoxon, analysis of variance/Tukey, and paired and unpaired t-tests (α = 0.05). Results: No significant difference was found in the volume increase and uninstrumented surface area between PDL and HEDM (p > 0.05). PDL had a higher percentage of debris than HEDM in the middle and apical thirds (p < 0.05). The FPDL protocol resulted in less debris and uninstrumented surface area for PDL and HEDM (p < 0.05). This protocol, with HEDM, reduced debris in the middle and apical thirds and uninstrumented surface area in the apical third (p < 0.05). Conclusions: High percentages of debris and uninstrumented surface area were observed after preparation of flattened root canals. The HEDM, Flatsonic tip, and 25/0.03 instrument protocol enhanced cleaning in flattened root canals.

• Restorative Dentistry and Endodontics
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• 제42권4호
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• pp.282-289
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• 2017

Objectives: It was aimed to compare the cyclic fatigue resistances of ProGlider (PG), One G (OG), and HyFlex EDM (HEDM) nickel titanium glide path files in single- and double-curved artificial canals. Materials and Methods: 40 PG (16/0.02), 40 OG (14/0.03), and 40 HEDM (10/0.05) single-file glide path files were used in the present study. Sixty files were subjected to cyclic fatigue test by using double-curved canals and 60 files by using single-curved canal (n = 20). The number of cycles to fracture (NCF) was calculated and the length of the fractured fragment (FL) was determined by a digital micro-caliper. Twelve pieces of fractured files were examined with scanning electron microscope to determine fracture types of the files (n = 2). The NCF and the FL data were analyzed using one-way analysis of variance and post hoc Tukey test using SPSS 21 software (p < 0.05). Results: In all of the groups, NCF values were significantly lower in double-curved canals when compared to single-curved canals (p < 0.05). For both of single- and double-curved canals, NCF values of HEDM group in apical and coronal curvatures were found to be significantly higher than NCF values of PG and OG groups (p < 0.05). In both of single- and double-curved canals, NCF value of PG group was found significantly higher than OG group (p < 0.05). Conclusions: Within the limitations of this study, HEDM glide path files were found to have the highest cyclic fatigue resistance in both of single- and double-curved canals.

• Journal of Dental Anesthesia and Pain Medicine
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• 제22권4호
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• pp.267-275
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• 2022

Background: Various instrument kinematics used in single-visit endodontics influence the occurrence of pain after endodontic therapy. This study aimed to evaluate the occurrence of pain after mechanical instrumentation with Hyflex EDM (HEDM) and WaveOne Gold (WOG) during single-visit endodontic therapy. Methods: Sixty patients diagnosed with asymptomatic irreversible pulpitis and normal apical tissues in mandibular premolar teeth were included in the study for single-visit root canal therapy. The patients were divided into two groups (n = 30) according to the rotary instrument used during root canal preparation (group A [HEDM] and group B [WOG]). Pain was evaluated after endodontic therapy at 8, 24, and 48 h intervals using the visual analog scale (VAS). Data obtained were analyzed using the chi-square test, independent t-test, MannWhitney U test, and Wilcoxon matched-pairs test. Results: Statistically significant differences were observed between the two groups (P < 0.001) at 8, 24, and 48 h, with WOG exhibiting less pain than HEDM files. Conclusion: Postoperative pain was lower in the WOG file system than in the HEDM file system after single-visit root canal therapy at 8, 24, and 48 h.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1993년도 제1회 학술강연회논문집
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• pp.34-37
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• 1993

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4341-4346
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• 2011

Impact sensitivity, one of the most important screening factors for novel high energy density materials (HEDMs), was predicted by use of quantitative structure-property relationship (QSPR) based on the electrostatic potential (ESP) values calculated on the van der Waals molecular surface (MSEP). Among various 3D descriptors derived from MSEP, we utilized total and positive variance of MSEP, and devised a new QSPR equation by combining three other parameters. We employed 37 HEDMs bearing a benzene scaffold and nitro substituents, which were also utilized by Rice and Hare. All the molecular structures were optimized at the B3LYP/6-31G(d) level of theory and confirmed as minima by the frequency calculations. Our new QSPR equation provided a good result to predict the impact sensitivities of the molecules in the training set including zwitterionic molecules.

• 대한화학회지
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• 제60권1호
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• pp.9-15
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• 2016

폭발성능이 높은 HMX와 폭발성능은 떨어지지만 안정성이 높은 LLM-116의 분자복합체인 HMX/LLM-116 공결정(cocrystal)의 폭발 속도, 폭발 압력 그리고 열역학적 안정성에 대하여 이론적으로 연구하였다. 각 분자 구조는 B3LYP/cc-pVTZ 수준까지 최적화 하였으며 가장 약한 방아쇠 결합(trigger bond)과 클러스터에 대한 결합에너지를 계산 하여 열역학적 안정성을 확인하였다. 보다 정확한 에너지를 계산하기 위해 MP2 이론 수준에서 한 점(single point) 에너지를 계산하였으며, monte carlo integration 계산을 통해 밀도를 계산 하였다. 엔탈피는 CBS-Q 이론 수준에서 계산하였으며, 폭발 속도와 폭발 압력은 Kamlet-Jacobs 방정식을 이용하여 계산하였다.

• 대한화학회지
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• 제66권3호
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• pp.185-193
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• 2022

본 연구에서는 tetrazine과 oxadiazole 등의 질소가 많이 함유되어 있는 헤테로 고리화합물을 가진 음이온과 NH₂OH, NH₂NH₂, CH₈N₆, C₂H₅N₅ 등의 양이온들과의 이온 결합을 통하여 생성된 에너지 염(energetic salts)에 대하여 열역학적 안정성, 밀도, 그리고 폭발 성능 등을 밀도 범함수 이론(dentisy functional theory, DFT)을 이용하여 계산하고 기존의 고성능 에너지 물질들과 비교하였다. 분자 구조 최적화 및 안정화 에너지는 B3LYP/cc-pVDZ 이론 수준에서 그리고 엔탈피 계산은 G2MP2 이론 수준에서 계산하였으며 폭발 성능은 Kamlet-Jacobs 방정식을 통하여 계산하였다. 결과적으로 크기가 작은 NH₃OH⁺(1)와 NH₂NH₃⁺(2) 양이온을 활용한 에너지 염은 폭발 성능 향상에 도움이 되며, 상대적으로 아미노기(-NH₂)가 많은 CH₉N₆⁺(3) 양이온은 안정성을 높이는데 효과적일 것으로 예측되었다.