• Progress in Medical Physics
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• v.9 no.1
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• pp.55-64
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• 1998

In recent, the demand of development of the high dose rate brachytherapy source increased for substitute for Co-60 source by iridium source, since the supplying Co-60 source is very depressed and the high dose rate brachytherapy sources are entirely imported from the abroad. This study investigated the exposure rates and isotropic dose distributions for the Ir-192 source produced from $\^$191/Ir(n,r)$\^$192/Ir by nuclear reactor in Korea Atomic Energy Research Institute. The activity of source was obtained an 1.012 Ci (the initial activity without encapsulation was 2,87Ci) by measurement with encapsuled stainless steel. The exposure rate of provided Ir-192 source was determined on 6.36 ${\pm}$ 0.147 Rm$^2$/h-GBq (2.350 ${\pm}$ 0.054 Rcm$^2$/mCi-hr) within ${\pm}$ 2.2% discrepancy with IC-10 ion chamber (0.14 cc) which was mounted on the acrylic jig to 5, 10 and 20 cm from the center of source. The calculated doses with 22 most significant spectrum lines were corrected with intrinsic efficiency of the germanium detector were compared to measured exposure dose rates within ${\pm}$3.8 % discrepancy. The authors confirmed the high dose rate Ir-192 source could be replaced the long decayed Co-60 source via investigation of the isotropic dose distributions in lateral, source axis and diagonal direction of source center are very closed to within 3% uncertainties. Especially, this exposure rate constant and isotropic dose distribution will be fundamental to build the high dose rate source and develop the computed therapy planning system.

• Progress in Medical Physics
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• v.23 no.1
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• pp.54-61
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• 2012

A polymer gel dosimeter was fabricated. A 3-dimensional dosimetry experiment was performed in the small field of the photon of the cyberknife. The dosimeter was installed in a head and neck phantom. It was manufactured from the acrylic and it was used in dosimetry. By using the head and neck CT protocol of the CyberKnife system, CT images of the head and neck phantom were obtained and delivered to the treatment planning system. The irradiation to the dosimeter in the treatment planning was performed, and then, the image was obtained by using 3.0T magnetic resonance imaging (MRI) after 24 hours. The dose distribution of the phantom was analyzed by using MATLAB. The results of this measurement were compared to the results of calculation in the treatment planning. In the isodose curve on the axial direction, the dose distribution coincided with the high dose area, 0.76mm difference on 80%, rather than the low dose area, 1.29 mm difference on 40%. In this research, the fact that the polymer gel dosimeter and MRI can be applied for analyzing a small field in a 3 dimensional dosimetry was confirmed. Moreover, the feasibility of using these for the therapeutic radiation quality control was also confirmed.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.4
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• pp.321-327
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• 2020

Purpose: The purpose of this study was to measure and compare the strain value exerted on the cervical area using different screw tightening protocols in implant-supported, screw-retained 3-unit prostheses. Materials and methods: Strain gauges were attached to four implants: two external and two internal. Thereafter, two study model were designed each type using acrylic resin. CAD-CAM was used to design hex and nonhex abutments for each group (EH, ENH, IH, and INH group) and Screw-cement-retained prostheses were also designed using a nonprecious base metal. Abutment was fixed with 10 Ncm torque, and the prosthesis was cemented. Screws were fixed with 30 Ncm torque using different three protocols. After 5 min, the strain gauge level was measured, and group analysis was performed (α=.05). Results: External group showed significantly lower strain values than internal group and the EH group showed significantly lower strain values than the ENH group (P<.05). There was no difference in strain value based on the types of screw tightening protocols in same group (P>.05). The IH group exhibited significantly higher strain values than the INH group and the IH group showed a significant difference in strain values based on the types of screw tightening protocols used (P<.05). Conclusion: There was no significant effect on the external type in the implant-supported, screw-retained prostheses. However, strain values were high in the internal type, and the types of screw tightening protocol significantly affected these implants.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.2
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• pp.149-159
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• 2006

Statement of problem. Porcelain repair mainly involves replacement with composite resin, but the bond strength between composite resin and all-ceramic coping materials has not been studies extensively. Purpose. The objective of this study was to investigate the influence of composite resin and ceramic etching pattern on shear bond strength of Empress2 ceramic and observe the change of microstructure of ceramic according to etching methods. Material and methods. Eighty-five cylinder shape ceramic specimens (diameter 5mm, IPS Empress 2 core materials) embeded by acrylic resin were used for this study. The ceramic were specimens divided into sixteen experimental groups with 5 specimens in each group and were etched with phosphoric acid(37%, 65%) & hydrofluoric acid (4%, 9%) according to different etching times(30s, 60s, 120s 180s). All etched ceramic surfaces were examined morphologically using SEM(scanning electron microscopy). Etched surfaces of ceramic specimens were coated with silane (Monobond-S) & adhesive(Heliobond) and built up composite resin using Teflon mold. Accomplished specimens were tested under shear loading until fracture on universal testing machine at a crosshead speed 1mm/min; the maximum load at fracture(kg) was recorded. Shear bond strength data were analyzed with one way ANOVA and Duncan tests.(P<.05) Results. Maximum shear bond strength was $30.07{\pm}2.41(kg)$ when the ceramic was etched with 4% hydrofluoric acid at 120s. No significant difference was found between phosphoric etchant group and control group with respect to shear bond strength. Conclusion. Empress 2 ceramic surface was not etched by phosphoric acid, but etched by hydrofluoric acid.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.2
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• pp.173-180
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• 2006

Objectives The aim of this study is to compare the quality of root canal preparation completed using MFile-$System^{(R)}$ instrument ( Komet, Gebr.Brsaseler, Germany) and conventional stainless steel file in the canals of Maxillary molar teeth that had a canal curvature between $25^{\circ}$ or more Materials & Methods Buccal canals of 24 first and second maxillary molar teeth, extracted for periodontal and prosthetic reasons were used. Tissue fragments and calcified debris were removed from teeth by scaling and the teeth were stored in 10% formalin solution for 24 hour. Then, teeth were stored in saline until used. To be included the roots had to have completed formed apices and angle of curvature ranging between $25^{\circ}$ or more according to the criteria described by Schneider(1971). Palatal and Second mesiobuccal canals were not included. Teeth were embedded into transparent acrylic. The teeth were randomly divided into two experimental groups. All teeth were scanned by Dental CT (PSR9000N, Asahi, Japan) to determine the root canal shape before instrumentation. Image slices were prepared from the apical end point to the pulp chamber. The first two sections were 2 mm from the apical end of root and 2 mm below the orifice. Further section was recorded, dividing the distance between the sections of apical and coronal levels into two equal lengths. 12 teeth were instrumented using stainless steel fileand another 12 teeth were instrumented using MFile-$System^{(R)}$. Following the completion of the instrumentation, the teeth were again scanned and compared with the cross sectional images taken prior to canal preparation. Amount of transportation and centering ability was assessed. Student's t-test was used for statistical analysis. Result Less transportation occurred with MFile-$System^{(R)}$ rotary instrumentation than stainless steel instrument. MFile-$System^{(R)}$ had better centering ability than stainless steel instrument. Conclusion MFile-$System^{(R)}$ rotary instrumentation transported canals less and had good centering ability.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.411-418
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• 2005

Polymer-modified mortar and concrete are prepared by mixing either a polymer or monomer in a dispersed, or liquid form with fresh cement mortar and concrete mixtures, and subsequently curing, and if necessary, the monomer contained in the mortar or concrete is polymerized in situ. Although polymers and monomers in any form such as latexes, water-soluble polymers, liquid resins, and monomers are used in cement composites such as mortar and concrete, it is very important that both cement hydration and polymer phase formation proceed well the yield a monolithic matrix phase with a network structure in which the hydrated cement phase and polymer phase interpenetrate. In the polymer-modified mortar and concrete structures, aggregates are bound by such a co-matrix phase, resulting in the superior properties of polymer-modified mortar and concrete compared to conventional mortar and concrete. The purpose of this study is to obtain the necessary basic data to develope appropriate latexes as cement modifiers, and to clarify the effects of the monomer ratios and amount of emulsifier on the properties of the polymer-modified mortars using methyl methacrylate-butyl acrylate(MMA/BA) and methyl methacrylate-ethyl acrylate(MMA/EA) latexes. The results of this study are as follows, the water absorption, chloride ion penetration depth and carbonation depth of MMA/BA-modified mortar are lowest. However, they are greatly affected by the polymer-cement ratio rather than the bound MMA content and type of polymer.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.273-283
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• 2010

This study evaluated the effect of 3 different compatible screws on the detorque values in a multiple implant-supported superstructure and single implant abutments. An implant superstructure directly connected to 4 implants was screwed to 6 experimental dental stone casts made by acrylic resin splinted impressions, using 20 Ncm. The detorque values of screws were measured twice. Three compatible abutment screws used in this study were TorqTite screw, Gold-Tite screw, and, Titanium screw. And, using single implant abutments (GoldAdapt Engaging abutments), the detorque values of 3 different screws were measured twice on 2 implants of 5 experimental casts. According to statistical analysis of detorque values using mixed model at a .05 level of significance, no statistically significant differences among 3 different compatible screws were found in a multiple implant-supported superstructure (p>0.05). But, in single implant abutments, statistically significant differences among 3 different compatible screws were found (p=0.0175). The detorque values of TorqTite(p=0.0462) and Titanium(p=0.0348) screws were significantly higher than those of Gold-Tite screw, but no statisticantly significantlydifferences were found between TorqTite and Titanium screws(p>0.05). Therefore, various compatible screws showed significant effects on the detorque values for single implant abutment, but, showed no significant effects for a multiple implant-supported superstructure.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.311-322
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• 2010

The purpose of this study was to evaluate the bond strengths between IPS e.max Press and four different types of resin cements that often used for esthetic restoration. Disc shaped IPS e.max Press blocks(N=40, diameter: 12mm, thickness: 3mm) were fabricated according to the manufacture's instruction and cleaned with ultrasonic cleaner. They were embedded into an autopolymerizing acrylic resin. Fourty cylinder shaped resin block(Filtek Z350, diameter: 4.5mm, thickness: 3mm) were fabricated using a plastic tube. Each specimens were randomly divided into 4 experimental group and bonded each other using 4 different resin cements(Variolink II(light-cure), Variolink II(dual-cure), Calibra, Super-Bond C&B) according to the manufactures' recommendations. All the specimens were stored in normal saline at $37^{\circ}C$ for 24 hours before test. Universal testing machine at a crosshead speed of 1mm/min was used to evaluate the shear bond strength. The data were statistically analyzed using one-way ANOVA(P<.01). Multiple comparison was done by the Tukey HSD test. The shear bond strength of Super-Bond C&B to e.max was significantly lower than those of Calibra, Variolink II(light-cure), Variolink II(dual-cure) (P<.01). The shear bond strength of Calibra, Variolink II(light-cure), Variolink II(dual-cure) to e.max were not significantly different. The shear bond strengths of light-cure/dual-cure cement were higher than that of self-cure cement.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.323-337
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• 2010

The objective of this study was to examine the availability of the new impression coping by comparing with conventional coping in implant pick-up impression technique. Five implant fixtures were installed on #14, 21, 23, 25, 27 in acrylic resin model. That model with 5 fixtures was standard model, which was divided 3 groups; using new flag type impression coping, conventional impression coping splinted with self-curing resin, conventional impression coping without splinting. We made metal circular cones for calculation 3-dimensional coordinates by attaching to implant fixtures or analogs. Three-dimensional relationships of each model were calculated. Data was analyzed by multiple ANOVA and Bonferroni. The accuracy of impression between using new flag type impression coping and conventional impression coping did not show differences in 3 - dimensional analysis.Within limitations of this study, the new flag type impression coping is available in implant pick-up impression technique.

• Imaging Science in Dentistry
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• v.30 no.3
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• pp.155-158
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• 2000

The purpose of this paper is to explain the making procedure and the usage of receiver operating characteristic (ROC) curve for interpretation of radiographic images. The conventional radiograms obtained after the creation of the lesions in the acrylic plates and were enhanced in color. The observer were informed of which tooth to examine, the 'a priori' probability of a lesion present and the approximate diameter of the lesions. The two groups of films were interpreted separately by the same observer using the same rating scale. The following rating scale was used: A; definitely no lesion, B; probably no lesion, C; not sure, D; probably a lesion, and E; definitely a lesion. In analysis, for each observer the diagnostic results in terms of true positive (TP) and false positive (FP) decisions were plotted on a graph. The lowest point on the graph represents the TP and FP when only decisions designated as E according to the rating scale are included. The next point shows the TP and FP values when diagnoses designated as D are added and so forth. By connecting such plot points, a receiver operating characteristic (ROC) curves is obtained. The area under the curve represents the diagnostic accuracy resulting from a diagnostic performance at pure chance level and a value of 1.0 at perfect performance. This method has been known as an useful method to detect the minute difference for each radiographic technic, each observer and for the different lesion depths.