• Journal of dental hygiene science
• /
• v.14 no.2
• /
• pp.94-100
• /
• 2014

The purpose of this study was to evaluate the accuracy of digitized elastomeric impression materials of crown abutment, using non-contact white light scanner and virtual three-dimensional superimpositional analysis. The stone models and impressions were digitized white light scanner to create three-dimensional surface models. Stone models were used as CAD reference model (CRM). The resulting point clouds (ASC file) from digitization of impressions using converting software. Discrepancies between the points in the point clouds and CRM were measured by superimpositional software. Mean and standard deviation of values of discrepancies were analyzed by one-way ANOVA and multiple comparison (${\alpha}=0.05$). The mean discrepancy between the impressions for the extra-light body (XLB), light body (LB), and heavy body (HB) group were $5.10{\pm}1.45{\mu}m$, $6.30{\pm}1.87{\mu}m$, $9.80{\pm}1.52{\mu}m$, respectively. The different impression materials affected the digitization of impressions significantly (p<0.05). As a result, digitization of elastomeric impression materials on dental scanner was influenced by material sort.

• Tunnel and Underground Space
• /
• v.26 no.6
• /
• pp.508-515
• /
• 2016

In this study, we compared the stability of the pillars by using room and pillar mining method with the four models with different stiffness and pillar overlap ratio. The experimental models consist of two plaster models (overlap ratio 0%, 100%) and two cement models(overlap ratio 0%, 100%). The soft and hard rocks are modeled by plaster and cement models respectively. In these experiments, the model materials with strength values reflecting the calculated scaled factors not been used, so it is not a true scaled model test that reproduces in situ state in the laboratory. Experimental results show that the different overlap ratio pillars are one of the factors that can affect the stability of the mine.

• Clean Technology
• /
• v.19 no.2
• /
• pp.90-94
• /
• 2013

We investigated one-dimensional thermal conduction for gypsum objects incorporating oyster shell powder. We presumed that according to the portion of oyster shell in the hybrid structure conductive characteristics of that would also change as some physicochemical properties such as volatile organic compound (VOC) adsorption were found to be changed considerably. Based on Fourier's 2nd law of heat conduction an analytical analysis in a flat slab (one axis perpendicular to an infinite plane) was performed. We found that composition of oyster shell and conduction-related coefficients and parameters could greatly influence on the thermal profile of that conduction, and some model experiments also served for it in the affirmative.

• The korean journal of orthodontics
• /
• v.30 no.5 s.82
• /
• pp.565-578
• /
• 2000

The aim of this study was development of the Straight-Wire Appliance(SWA) suitable lot the treatment or Korean. To accomplish the object of this study, Korean adult with normal occlusion were selected with following criteria : 1) no functional abnormality in the craniofacial area, 2) good dental arch form and posterior occlusal relationship, 3) Angle Class I occlusal relationship, 4) no experience of orthodontic, nor prosthodontic treatment, especially, no dental treatment on labial and buccal surfaces of teeth, 5) good racial profile. Impression were taken for upper and lower dental arches or the selected normal occlusion samples and the orthodontic dental stone models were fabricated. 5 well-trained orthodontists had examined the acquired dental stone models to select study samples which satisfy the Six keys to optimal occlusion of Andrews. 155 pairs of dental stone models (92 pairs of Male, 63 of Female) were finally selected. 3 dimensional digitization were performed with the Coordinate Measuring Machine(CMM, MPC802, WEGU-Messtechnik, Germany) and measuring of Angulation, Inclination, In-and-Out, Molar offset angle and Arch form were accomplished with a measuring software to achieve data for the development of SWA. Before the measurement, error study was performed on the 3 dimensional digitization with CMM, and the analysis of reliability of computerized measuring method adapted in this study and conventional manual method Presented by Andrews was performed. Results of this study were as to)lows : 1. Equi-distance digitization with mesh size 0.25 mm, 0.5 mm and 1.0 mm were acceptable in 3 dimensional digitization of dental stone model with the CMM, and the digitization with 1.0 mm mesh size was recommendable in terms of efficiency. 2. Computerized measuring method with 3 dimensional digitization was more reliable than manual measuring method of Andrews. 3. Data were collected for the development of SWA suitable for the morphological characteristics of Korean with the computerized measuring method with 3 dimensional digitization.

• Tunnel and Underground Space
• /
• v.14 no.5
• /
• pp.381-390
• /
• 2004

In this study, scaled model tests were performed to investigate the deformation behaviors around twin tunnels. Eleven types of test models which had respectively different pillar widths, rock types and loading conditions were mode, where the modelling materials were the mixture of sand, plaster and water. The models with shallower pillar width were cracked under lower pressure than the models with thicker pillar width, and they showed the more tunnel convergences and the clear spatting failures. The models of hard rock were cracked under 50% higher pressure than the models of soft rock and they showed the less tunnel convergences. The failure and deformation behaviors of twin tunnels were also dependent on the loading conditions of models. Futhermore, the results of FLAC analysis were qualitatively coincident with the test results.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
• /
• 2011.11a
• /
• pp.369-372
• /
• 2011

본 연구에서는 철도차량의 실물화재에 대한 열방출율을 축소모형으로 예측하기 위해 실험적인 조건들을 연구하였다. 축소모형의 크기는 지하철 전동차의 1/10 스케일을 적용하여 길이 1.89m, 너비 0.295m, 높이 0.235m 이며 15mm의 석고보드를 사용하였다. 축소모형의 실험적 조건으로는 한쪽 면만 개방한 4개의 개구부 환기조건과 3mm, 6mm의 종이내장재를 이용하여 열방출율을 예측하여 보았다.

• The korean journal of orthodontics
• /
• v.37 no.3 s.122
• /
• pp.212-219
• /
• 2007

Objective: The purpose of this study was to provide an anatomical reference for cortical bone and soft tissue thickness, and the attached gingiva width in the mandible. Methods: Fifteen males and fifteen females participated in this study. An acrylic template was fabricated and the radiopaque markers were bonded on the estimated alveolar crest to take measurements of the hard and soft tissue thickness at the same locations. CT images were taken in samples wearing an acrylic template. Cortical bone and soft tissue thickness were measured at 2, 4, 6 and 8 mm from the alveolar crest in interradicular spaces from central incisor to first permanent molar. The attached gingival width was calibrated. Results: Cortical bone thickness was $1.33{\pm}0.38mm$ and soft tissue thickness was $1.49{\pm}0.54mm$. Cortical bone thickness was increased in the posterior area, while it was not the case for the soft tissue thickness. In addition, the total thickness was $2.82{\pm}0.70$. The attached gingival width was wider in the anterior area compared to that in posterior area. Conclusion: These results suggest that the attached gingiva width should be considered upon placement of mini-implants in the mandibular posterior area for orthodontic anchorage.

• The Journal of Korean Academy of Prosthodontics
• /
• v.53 no.2
• /
• pp.111-119
• /
• 2015

Purpose: The objective of this study was to evaluate the accuracy of a stereolithographic surgical guide that was made with information from intraoral digital impressions and cone beam CT (CBCT). Materials and methods: Six sets of resin maxilla and mandible models with missing teeth were used in this study. Intraoral digital impressions were made. The virtual models provided by these intraoral digital impressions and by the CBCT scan images of the resin models were used to create a surgical guide. Implant surgery was performed on the resin models using the surgical guide. After implant placement, the models were subjected to another CBCT scan to compare the planned and actual implant positions. Deviations in position, depth and axis between the planned and actual positions were measured for each implant. Results: The mean deviation of the insertion point and angulation were 0.28 mm and $0.26^{\circ}$, apex point were 0.11 mm and 0.14 mm respectively. The implants were situated at a mean of 0.44 mm coronal to the planned vertical position. Conclusion: This study demonstrates that stereolithographic surgical guides created without the use of impressions and stone models show promising accuracy in implant placement.

• The Journal of Korean Academy of Prosthodontics
• /
• v.58 no.2
• /
• pp.86-94
• /
• 2020

Purpose: The purpose of this study is to compare the volume stability depending on the mixing methods and storage time for the conventional alginate and extended-pour alginate. Materials and methods: An arch-shaped metal model was fabricated, and one conventional alginate and two extended-pour alginates were used to take impressions using different mixing methods (hand and automatic). 120 impressions were taken (40 per each alginate) and stone models were made in accordance with the different storage times (immediate, 2 days, 5 days, and 6 days). The models were scanned with a 3D table scanner and dimensional change was measured by superimposing the scan data. Using SAS 9.4 (SAS Institute Inc., Cary, NC, USA), the general linear model and Tukey's post hoc test was conducted for statistical analysis (P<.001). Results: There was no statistically significant difference in the dimensional accuracy between two mixing methods, and the volume change was minimum when the stone was poured immediately in all groups. Dimensional accuracy showed a statistically significant difference between groups after 2 days of storage, and extended-pour alginate showed higher accuracy after 5 days of storage comparing to conventional one. Large amounts of volume change were showed at 2 - 5 days for conventional alginate and at 5 - 6 days for extended pour alginate. Conclusion: The mixing method of alginate does not affect volume stability. Although extended-pour alginate has better volume stability than conventional alginate for a long time, it is recommended to pour stone as soon as possible.

• The KIPS Transactions:PartA
• /
• v.12A no.6 s.96
• /
• pp.515-522
• /
• 2005

This paper presents a method for effectively modeling inlay/onlay prostheses restoring a tooth that are partially destroyed. An inlay/onlay is composed of internal surface adhering to an abutment, and external surface revealed to the outside sight. Internal surfaces are modeled using Minkowski sum expanding the grinded surface parts of abutments so that the internal surfaces can adhere to the abutments with closer contact. In modeling external surfaces, we exploit 3D mesh deformation techniques: DMFFD(direct manipulation free-form deformation)[19] and MWD(multiple wires deformation)[17] with three kinds of informations: standard teeth models, mesh data obtained by scanning a plaster cast of a patient's tooth, FGP(functionally guided plane) measuring the occlusion of the patients's teeth. The standard teeth models are used for building up the basic shapes of external surfaces, while the plaster fast and FGP data are used for reflecting the unique properties of adjacent md occlusal surfaces of the patients's teeth, which are slightly different to each other but very important for correct functioning. With these informations as input data, the adjacent and occlusal surfaces are automatically generated as mesh data using the techniques of DMFFD and m, respectively. Our method was implemented so that inlay/onlay prostheses fan be designed more accurately by visualizing the generated mesh models with requirements by dentists.