• Imaging Science in Dentistry
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• 제49권2호
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• pp.123-130
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• 2019

Purpose: This study was conducted to characterize the relationship of the angulation between the tooth root axis and alveolar bone axis with anterior alveolar(AA) arch forms and sagittal root position (SRP) in the anterior esthetic region using cone-beam computed tomography (CBCT) images. Materials and Methods: CBCT images that met the inclusion and exclusion criteria were categorized using a recent classification of AA arch forms and a SRP classification. Then, the angulation of the root axis and the alveolar bone axis was measured using mid-sagittal CBCT images of each tooth. The relationships of the angulation with each AA arch form and SRP classification were evaluated using 1-way analysis of variance and a linear regression model. Results: Ninety-eight CBCT images were included in this study. SRP had a greater influence than the AA arch form on the angulation of the root axis and the alveolar bone axis(P<0.05). However, the combination of AA arch form and SRP was more predictive of the angulation of the root axis and the alveolar bone axis than either parameter individually. Conclusion: The angulation of the root axis and alveolar bone axis demonstrated a relationship with the AA arch form and SRP in teeth in the anterior esthetic region. The influence of SRP was greater, but the combination of both parameters was more predictive of root-to-bone angulation than either parameter individually, implying that clinicians should account for both the AA arch form and SRP when planning implant placement procedures in this region.

• The Journal of Advanced Prosthodontics
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• 제5권4호
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• pp.452-456
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• 2013

PURPOSE. The aim of this study was to evaluate the repeatability of the digitizing of silicon rubber impressions of abutment teeth by using a white light scanner and compare differences in repeatability between different abutment teeth types. MATERIALS AND METHODS. Silicon rubber impressions of a canine, premolar, and molar tooth were each digitized 8 times using a white light scanner, and 3D surface models were created using the point clouds. The size of any discrepancy between each model and the corresponding reference tooth were measured, and the distribution of these values was analyzed by an inspection software (PowerInspect 2012, Delcamplc., Birmingham, UK). Absolute values of discrepancies were analyzed by the Kruskal-Wallis test and multiple comparisons (${\alpha}$=.05). RESULTS. The discrepancy between the impressions for the canine, premolar, and molar teeth were $6.3{\mu}m$ (95% confidence interval [CI], 5.4-7.2), $6.4{\mu}m$ (95% CI, 5.3-7.6), and $8.9{\mu}m$ (95% CI, 8.2-9.5), respectively. The discrepancy of the molar tooth impression was significantly higher than that of other tooth types. The largest variation (as mean [SD]) in discrepancies was seen in the premolar tooth impression scans: $26.7{\mu}m$ (95% CI, 19.7-33.8); followed by canine and molar teeth impressions, $16.3{\mu}m$ (95% CI, 15.3- 17.3), and $14.0{\mu}m$ (95% CI, 12.3-15.7), respectively. CONCLUSION. The repeatability of the digitizing abutment teeth's silicon rubber impressions by using a white light scanner was improved compared to that with a laser scanner, showing only a low mean discrepancy between $6.3{\mu}m$ and $8.9{\mu}m$, which was in an clinically acceptable range. Premolar impression with a long and narrow shape showed a significantly larger discrepancy than canine and molar impressions. Further work is needed to increase the digitizing performance of the white light scanner for deep and slender impressions.

• The Journal of Advanced Prosthodontics
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• 제6권1호
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• pp.1-7
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• 2014

PURPOSE. The accuracy of a gypsum model (GM), which was taken using a conventional silicone impression technique, was compared with that of a polyurethane model (PM), which was taken using an iTero$^{TM}$ digital impression system. MATERIALS AND METHODS. The maxillary first molar artificial tooth was selected as the reference tooth. The GMs were fabricated through a silicone impression of a reference tooth, and PMs were fabricated by a digital impression (n=9, in each group). The reference tooth and experimental models were scanned using a 3 shape convince$^{TM}$ scan system. Each GM and PM image was superimposed on the registered reference model (RM) and 2D images were obtained. The discrepancies of the points registered on the superimposed images were measured and defined as GM-RM group and PM-RM group. Statistical analysis was performed using a Student's T-test (${\alpha}=0.05$). RESULTS. A comparison of the absolute value of the discrepancy revealed a significant difference between the two groups only at the occlusal surface. The GM group showed a smaller mean discrepancy than the PM group. Significant differences in the GM-RM group and PM-RM group were observed in the margins (point a and f), mesial mid-axial wall (point b) and occlusal surfaces (point c and d). CONCLUSION. Under the conditions examined, the digitally fabricated polyurethane model showed a tendency for a reduced size in the margin than the reference tooth. The conventional gypsum model showed a smaller discrepancy on the occlusal surface than the polyurethane model.

• Restorative Dentistry and Endodontics
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• 제47권1호
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• pp.1.1-1.13
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• 2022

Objectives: This study assessed the shape and anatomical relationship of the mental foramen (MF) to mandibular posterior teeth in an Indian sub-population. Materials and Methods: In total, 475 existing cone-beam computed tomography records exhibiting 950 MFs and including the bilateral presence of mandibular premolars and first molars were assessed. Images were evaluated 3-dimensionally to ascertain the position, shape, and anatomical proximity of MFs to mandibular teeth. The position and shape of MFs were measured and calculated. The Pythagorean theorem was used to calculate the distance between the root apex of the mandibular teeth and the MF. Results: MFs exhibited a predominantly round shape (left: 67% and right: 65%) followed by oval (left: 30% and right: 31%) in both males and females and in different age groups. The root apices of mandibular second premolars (left: 71% and right: 62%) were closest to the MF, followed by distal to the first premolars and mesial to the second premolars. The mean vertical distance between the MF and the nearest tooth apex calculated on sagittal sections was 2.20 mm on the right side and 2.32 mm on the left side; no significant difference was found according to sex or age. The distance between the apices of the teeth and the MF was ≥ 4 mm (left; 4.09 ± 1.27 mm and right; 4.01 ± 1.15 mm). Conclusions: These findings highlight the need for clinicians to be aware of the location of the MF in treatment planning and while performing non-surgical and surgical endodontic procedures.

• 소성∙가공
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• 제17권2호
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• pp.124-129
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• 2008

Net shape forging technologies give many effects into the costs and qualities for the finished products. So, the studies to reduce the additional machining amount are very important in forging industry. Specially, there are two main topics in cold forging industry, such as, tool life and precision forging. In this study, new forging technique was proposed to eliminate the machining process for fixing up the length and improve the lead accuracy of gear. The luck-up hub is manufactured through many processes, such as upsetting, piercing and direct extrusion. The gear is formed in direct extrusion process; however, lead accuracy of the gear is over allowance limit. Therefore, the additional sizing process must be added. In this study, process design for closed-die forging of a lock-up hub used for a component of automobile transmission was made using three-dimensional finite element simulations, and the strain distributions and velocity distributions are investigated through the post processor. The rigid-plastic finite-element method for back pressure forging has been used in order to reduce development time and die cost. Using the FEM simulation, we found the optimum value of back pressure. The prototypes of lock-up hub parts were forged into the net-shape. In the experiment, lead precision of tooth are measured by the CCMM(Contact Coordinate Measuring Machine). The dimensional accuracy of forged part was improved up to the 40% when back press was applied.

• 대한치과의사협회지
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• 제55권1호
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• pp.63-70
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• 2017

Materials and methods: Sixty extracted premolars were assigned to three groups according to the root canal system (Weine's classification; type I, II and III) of 20 teeth each using radiographic examination. The root tip was cut horizontally 1 mm from the anatomical apex and the apical cross-section was visualized using microscope at x50 magnification and photographed. Minimum and maximum apical root canal diameter of each tooth was measured and classified into three types by canal morphology (round, oval and flattened shape). Statistical analysis was performed to compare the apical root canal diameter and morphology according to the root canal system. Results: In apical root canal morphology at cross-sectional view, the most common shape was round in type I, flat in type II, and oval in type III. In apical root canal diameters at cross-sectional view, there was a significant difference between the minimum and maximum diameter in all types (p<0.05). The maximum diameter was 0.331 mm in type I, 0.519 mm in type II, and 0.310 mm in type III. There was a significant difference among type I, III and type II (p<0.05). Conclusion: The morphology and diameter of apical root canal was different according to the root canal system. Therefore, clinicians should consider the apical file size in view of the apical root canal shape according to the root canal system.

• 대한심미치과학회지
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• 제31권2호
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• pp.47-55
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• 2022

임플란트 수복 후 발생하는 인접면 공간개방으로 인한 식편압입은 임플란트를 시술한 환자에게 매우 흔히 발생하는 현상이다. 이는 임플란트와 치아의 움직임 기전이 달라 발생하며 시간이 경과하면 30-60% 정도 발생하는데, 기여요인으로는 악골(하악), 부위(구치부), 인접치(실활치) 및 대합치(자연치 또는 임플란트) 등이 있다. 이런 현상을 방지할 수는 없으나 최소화하기 위한 노력을 기울여야 한다. 가급적 이상적인 인접접촉을 가지도록 상부 1/3에 협설로 인접치와 대칭적인 인접면 형태를 만들어 주기 위해 오목한 형태나 하방이 풍융한 인접치 형태를 수정하고 수복할 때는 다른 조건을 수정하여 변연융선의 높이를 맞추어 주어야 한다. 불규칙한 교합평면은 예후를 나쁘게 하는 원인이므로 정출된 대합치를 수정하고 기능이상을 유발하는 원심협측 교두를 수정함으로써 이상적인 교합평면을 회복함으로써 식편압입 현상을 최소화시켜야 한다.

• 구강회복응용과학지
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• 제20권2호
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• pp.109-120
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• 2004

덴틴, 에나멜, 투명 일반도재를 페이스트화 하여 치아의 색상, 투명도 및 구조를 고려한 복합층구성물을 미리 제조하여 심미수복물을 용이하게 제작하는 공정을 개발하였다. 페이스트 상태에서 성형성과 유동특성이 확보되고, 소성 후 색도, 및 강도 등의 제특성들을 만족시킬 수 있는 결합제 시스템으로서 UV (creation universal liquid)를 선정하였고 조성 및 최적화가 이루어졌다. 페이스트는 24시간까지도 점성 및 작업성이 유지되었고, 이를 이용하여 복합층 구성물의 용이한 성형이 가능하였다. 소성수축률은 15.2%로 기존의 방법으로 제조한 시편에 비해 0.8% 낮았으나 유의차는 없었다. spectrophotometer에 의한 색도특성 관찰결과 덴틴재를 기존 제조방식으로 제조한 시편과 페이스트형 도재 시스템으로 제조한 시편에서 $L^*$, $a^*$, $b^*$가 각각 60~80, -1.5~+1.5, 5~20 사이의 값을 나타냄을 확인하였다. 측정값으로부터 구해진 제조방식에 따른 시편 간의 색차(${\Delta}E^*$)는 0.156으로 극히 근소한 차이를 나타냄을 확인하였다. 유기물 첨가에 따른 소성 후 잔류물 함량은 검출오차범위 내에 있었으며, 기존의 제조방식으로 제조한 소성체와 페이스트형 도재 시스템을 이용한 소성체의 강도는 각각 $70{\pm}4MPa$, $74{\pm}3MPa$으로 유의차가 없이 근사한 물성을 나타내었다. 페이스트형 도재를 이용한 도재축성법을 기존방법과 비교분석한 결과, 기계적 또는 광학적 특성의 변화없이 적용이 가능하였다.

• 대한소아치과학회지
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• 제40권3호
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• pp.149-158
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• 2013

이 연구의 목적은 치과용 3차원 Come-beam CT 영상을 이용하여 정중과잉치의 형태와 매복 양상 및 연관된 합병증에 대해 평가하는 것이다. 2007년부터 2012년까지 정중과잉치를 주소로 조선대학교 치과병원 소아치과에 내원한 280명의 환아의 cone-beam CT 영상을 평가하였다. 매복된 정중과잉치는 여아보다 남아에서 더 빈번했고, 약 3.3 : 1의 비율을 보였으며 6~8세에서 가장 많이 관찰되었다. 환자당 정중과잉치의 개수는 1.38개였다. 대부분의 정중과잉치는 원추형(79.5%)이었으며, 역위방향(48.6%)으로 위치하고 있었다. 근원심적 위치로는 정중부(81.8%)가 가장 흔했고, 수직적으로는 치경부 근처(60.3%)에 가장 많이 분포하였으며, 순구개측 위치로는 구개측(73.8%)에 가장 많이 위치였다. 정중과잉치의 47.5%에서 합병증이 관찰되었고 인접치 변위와 맹출 지연이 가장 흔했다. 과잉치의 형태와 수직적 위치, 그리고 순구개측 위치가 합병증과 상관관계를 보였다. Cone-beam CT는 매복된 정중과잉치에 대한 3차원적 위치 정보와 정확한 영상을 제공하였다.

• 대한기관식도과학회지
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• 제17권2호
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• pp.116-119
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• 2011

Computed tomography with virtual bronchoscopy shows inner shape of trachea and major bronchi with three-dimensional images. Virtual bronchoscopy can be used in cases of suspected foreign body aspiration. Virtual bronchoscopy shows the exact location of the obstructive lesion before conventional bronchoscopy. If the chest radiography is normal or suggests aspirated foreign body, virtual bronchoscopy can be considered before conventional bronchoscopy. We experienced a case of false-tooth foreign body extracted under bronchoscopy. In this case, virtual bronchoscopy was made retrospectively giving useful information about shape and orientation regarding foreign body.