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Effect of repetitive pecking at working length for glide path preparation using G-file
하정홍,전효진,Rashid El Abed,장석우,김성교,김현철 대한치과보존학회 2015 Restorative Dentistry & Endodontics Vol.40 No.2
Objectives: Glide path preparation is recommended to reduce torsional failure of nickeltitanium (NiTi) rotary instruments and to prevent root canal transportation. This study evaluated whether the repetitive insertions of G-files to the working length maintain the apical size as well as provide sufficient lumen as a glide path for subsequent instrumentation. Materials and Methods: The G-file system (Micro-Mega) composed of G1 and G2 files for glide path preparation was used with the J-shaped, simulated resin canals. After inserting a G1 file twice, a G2 file was inserted to the working length 1, 4, 7, or 10 times for four each experimental group, respectively (n = 10). Then the canals were cleaned by copious irrigation, and lubricated with a separating gel medium. Canal replicas were made using silicone impression material, and the diameter of the replicas was measured at working length (D0) and 1 mm level (D1) under a scanning electron microscope. Data was analysed by one-way ANOVA and post-hoc tests (p = 0.05). Results: The diameter at D0 level did not show any significant difference between the 1, 2, 4, and 10 times of repetitive pecking insertions of G2 files at working length. However, 10 times of pecking motion with G2 file resulted in significantly larger canal diameter at D1 (p < 0.05). Conclusions: Under the limitations of this study, the repetitive insertion of a G2 file up to 10 times at working length created an adequate lumen for subsequent apical shaping with other rotary files bigger than International Organization for Standardization (ISO) size 20, without apical transportation at D0 level.
은 나노선 펨토초 레이저 조사에 의해 유도되는 전자기장 및 온도장 수치 해석
하정홍,김동식,Ha, Jeonghong,Kim, Dongsik 한국레이저가공학회 2015 한국레이저가공학회지 Vol.18 No.1
This work performed numerical analysis of electromagnetic field and thermal phenomena occurring in femtosecond laser irradiation of silver nanowires. The local electric field enhancement was computed to calculate the optical energy dissipation as a Joule heating source and the thermal transport was analysed based on the two-temperature model (TTM). Electron temperature increased up to 1000K after 50fs and its spatial distribution became homogeneous after 80fs at the fluence of 100mJ/cm2. The result of this work is expected to contribute to revealing the photothermal effects on silver nanowires induced by femtosecond laser irradiation. Although the highest increase of lattice temperature was substantially below the melting point of silver, the experimental results showed resolidification and fragmentation of the silver nanowire into nanoparticles, which cannot be explained by the photothermal mechanism. Further studies are thus needed to clarify the physical mechanisms.
Screw-in forces during instrumentation by various file systems
하정홍,김현철,곽상원,김성교 대한치과보존학회 2016 Restorative Dentistry & Endodontics Vol.41 No.4
Objectives: The purpose of this study was to compare the maximum screw-in forces generated during the movement of various Nickel-Titanium (NiTi) file systems. Materials and Methods: Forty simulated canals in resin blocks were randomly divided into 4 groups for the following instruments: Mtwo size 25/0.07 (MTW, VDW GmbH), Reciproc R25 (RPR, VDW GmbH), ProTaper Universal F2 (PTU, Dentsply Maillefer), and ProTaper Next X2 (PTN, Dentsply Maillefer, n = 10). All the artificial canals were prepared to obtain a standardized lumen by using ProTaper Universal F1. Screwin forces were measured using a custom-made experimental device (AEndoS-k, DMJ system) during instrumentation with each NiTi file system using the designated movement. The rotation speed was set at 350 rpm with an automatic 4 mm pecking motion at a speed of 1 mm/sec. The pecking depth was increased by 1 mm for each pecking motion until the file reach the working length. Forces were recorded during file movement, and the maximum force was extracted from the data. Maximum screwin forces were analyzed by one-way ANOVA and Tukey’s post hoc comparison at a significance level of 95%. Results: Reciproc and ProTaper Universal files generated the highest maximum screw-in forces among all the instruments while M-two and ProTaper Next showed the lowest (p < 0.05). Conclusions: Geometrical differences rather than shaping motion and alloys may affect the screw-in force during canal instrumentation. To reduce screw-in forces, the use of NiTi files with smaller cross-sectional area for higher flexibility is recommended.
하정홍,박상신 대한치과보존학회 2012 Restorative Dentistry & Endodontics Vol.37 No.4
Objectives: The purpose of this study was to investigate the screw-in effect and torque generation depending on the size of glide path during root canal preparation. Materials and Methods: Forty Endo-Training Blocks (REF A 0177, Dentsply Maillefer)were used. They were divided into 4 groups. For groups 1, 2, 3, and 4, the glide path was established with ISO #13 Path File (Dentsply Maillefer), #15 NiTi K-file NITIFLEX (Dentsply Maillefer), modified #16 Path File (equivalent to #18), and #20 NiTi K-file NITIFLEX, respectively. The screw-in force and resultant torque were measured using a custom-made experimental apparatus while canals were instrumented with ProTaper S1 (Dentsply Maillefer) at a constant speed of 300 rpm with an automated pecking motion. A statistical analysis was performed using one-way analysis of variance and the Duncan post hoc comparison test. Results: Group 4 showed lowest screw-in effect (2.796 ± 0.134) among the groups (p < 0.05). Torque was inversely proportional to the glide path of each group. In #20 glide path group, the screw-in effect and torque decreased at the last 1 mm from the apical terminus. However, in the other groups, the decrease of the screw-in effect and torque did not occur in the last 1 mm from the apical terminus. Conclusions: The establishment of a larger glide path before NiTi rotary instrumentation appears to be appropriate for safely shaping the canal. It is recommended to establish #20 glide path with NiTi file when using ProTaper NiTi rotary instruments system safely.
수치해석을 이용한 3D 프린팅용 세라믹 슬러리 코팅 품질 평가
하정홍(J. Ha),박준영(J. Park),박유진(Y. J. Park),고종완(J. W. Ko),김충수(C. Kim),김동현(D.-H. Kim) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
세라믹 3D 프린팅은 소재에 따라 슬러리, 분말, 벌크 소재 기반으로 분류할 수 있는데, 이 중 슬러리 소재 기반의 3D 프린팅 방법은 세라믹 분말의 함량 및 용매의 점도를 조절함으로써 고밀도의 세라믹 3D 프린팅 부품을 얻을 수 있다는 장점을 갖는다. 슬러리 기반의 3D 프린팅 부품의 품질은 세라믹 슬러리를 얼마나 균일하게 도포하느냐가 큰 변수로 작용한다. 슬롯 다이 코터(Slot Die Coater)는 길고 폭이 좁은 슬릿 형태의 노즐이 기판 위를 이동하며 슬러리를 분출하여 막을 형성시키는 방법으로, 고점도의 세라믹 슬러리의 도포를 위해 주로 사용되고 있다. 슬롯 다이 코팅 품질에 영향을 주는 주요 변수로는 점도, 접촉각, 표면장력 등의 슬러리 물성과 이송 속도, 코팅 간격 등의 코터 운전 조건, 그리고 다이 립 각도, 다이 립 길이, 노즐 간격 등의 다이 형상이 있다. 본 연구에서는 전사유체역학을 이용하여 슬롯 다이 코팅 방식을 이용한 세라믹 슬러리 코팅 공정에서의 코팅 특성을 평가하고자 한다. 이를 위해, 코터의 운전 조건과 다이의 형상에 따른 코팅 특성의 변화를 관찰하였다. 그리고, 해석 결과를 바탕으로 균일한 두께의 세라믹 슬러리 층을 얻기 위해 주요 공정 변수에 대한 최적화를 수행하였다.