• The Journal of Korean Academy of Prosthodontics
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• v.55 no.4
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• pp.381-388
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• 2017

Purpose: Unpredictable shrinkage of zirconia during sintering process causes discrepancy. Therefore, there have been attempts to reduce discrepancy by milling zirconia after sintering. However, due to the hardness of sintered zirconia, milling takes longer time, causes damage to the machine and causes chip formation. With customized zirconia block using the mean dimension of prepared natural dentition, it is expected to overcome these shortcomings. Materials and methods: The mean dimension of prepared natural dentition was analyzed as STL file after scanning of prepared teeth treated at SNUDH. The transverse, frontal and sagittal planes were set using Mimics and Photoshop. 3D volume was projected on each plane, and the outer line was measured through external tangent line, and the inner line was measured through inflection point of tangent line. Results: The mean height of prepared incisal (N = 57) is $6.60{\pm}1.05mm$, mesiodistal length is $2.98{\pm}0.73mm$, buccolingual length is $2.04{\pm}0.73mm$. The mean height of prepared premolar (N = 15) is $5.37{\pm}1.49mm$, mesiodistal length is $4.10{\pm}1.78mm$, buccolingual length is $5.86{\pm}1.55mm$. And the mean height of prepared molar (N = 13) is $5.11{\pm}1.29mm$, mesiodistal length is $6.80{\pm}1.18mm$, buccolingual length is $7.34{\pm}1.40mm$. Conclusion: Using the mean dimension of prepared natural dentition, it is expected to be able to fabricate customized zirconia block.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.4
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• pp.313-320
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• 2020

Purpose: The purpose of this study was to evaluate the machining precision and the marginal and internal fit of single restorations fabricated with three types of lithium disilicate ceramic blocks and to evaluate the correlation. Materials and methods: Single restorations were designed using a CAD software program. The crown designed model file was extracted from the CAD software program. Three types of lithium disilicate blocks (Rosetta; HASS, IPS e.max CAD; Ivoclar vivadent, VITA Suprinity; VITA) were milled using a milling machine. For the fabrication of the crown scanned model file, the intaglio surface of the restoration was digitized using a contact scanner. Then, using the three-dimensional inspection software (Geomagic control X; 3D Systems), the process of the overlap of the crown designed model and the scanned model and 3-dimensional analysis was conducted. In addition, the marginal and internal fit of the crowns was evaluated by a silicone replication method. The difference among three types of single ceramic crown was analyzed using a Kruskal-Wallis H test, and Spearman correlation analysis was performed to analyze the correlation between machining precision and fitness (α=.05). Results: There was a significant difference in the machining precision and the marginal and internal fit according to the type of ceramic block (P<.001). In addition, the machining precision and the marginal and internal fit were positively correlated (P<.001). Conclusion: The marginal fit of crowns fabricated according to the types of ceramic blocks was within the clinically acceptable range (< 120 ㎛), so it can be regarded as appropriate machining precision applicable to all clinical as aspects in terms of the marginal fit.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.1
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• pp.66-78
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• 2004

The objective of this study was to apply the vibration technique to reduce the viscosity of bonding adhesives and thereby compare the bond strength and resin penetration in enamel and dentin achieved with those gained using the conventional technique and vibration technique. For enamel specimens, thirty teeth were sectioned mesio-distally. Sectioned two parts were assigned to same adhesive system but different treatment(vibration vs. non-vibration). Each specimen was embedded in 1-inch inner diameter PVC pipe with a acrylic resin. The buccal and lingual surfaces were placed so that the tooth and the embedding medium were at the same level. The samples were subsequently polished silicon carbide abrasive papers. Each adhesive system was applied according to its manufacture's instruction. Vibration groups were additionally vibrated for 15 seconds before curing. For dentin specimen, except removing the coronal part and placing occlusal surface at the mold level, the remaining procedures were same as enamel specimen. Resin composite(Z250. 3M. U.S.A.) was condensed on to the prepared surface in two increments using a mold kit(Ultradent Inc., U.S.A.). Each increments was light cured for 40 seconds. After 24 hours in tap water at room temperature, the specimens were thermocycled for 1000cycles. Shear bond strengths were measured with a universal testing machine(Instron 4465, England). To investigate infiltration patterns of adhesive materials, the surface of specimens was examined with scanning electron microscope. The results were as follows: 1. In enamel the mean values of shear bond strengths in vibration groups(group 2, 4, 6) were greater than those of non-vibration group(group 1, 3, 5). The differences were statistically significant except AQ bond group. 2. In dentin, the mean values of shear bond strengths in vibration groups(group 2, 4, 6) were greater than those of non-vibration groups(group 1, 3, 5). But the differences were not statistically significant except One-Up Bond F group. 3. The vibration group showed more mineral loss in enamel and longer resin tag and greater number of lateral branches in dentin under SEM examination.

• Journal of Dental Rehabilitation and Applied Science
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• v.23 no.3
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• pp.249-257
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• 2007

State of problem : The use of zirconium oxide all-ceramic material provides several advantages, including a high flexural strength(>1000MPa) and desirable optical properties, such as shading adaptation to the basic shades and a reduction in the layer thickness. Along with the strength of the materials, the cementation technique is also important to the clinical success of a restoration. Nevertheless, little information is available on the effect of different surface treatments on the bonding of zirconium high-crystalline ceramics and resin luting agents. Purpose : The aim of this study was to test the effects of surface treatments of zirconium on shear bond strengths between bovine teeth and a zirconia ceramic and evaluate differences among cements Material and methods : 54 sound bovine teeth extracted within a 1 months, were used. They were frozen in distilled water. These were rinsed by tap water to confirm that no granulation tissues have left. These were kept refrigerated at $4^{\circ}C$ until tested. Each tooth was placed horizontally at a plastic cylinder (diameter 20mm), and embedded in epoxy resin. Teeth were sectioned with diamond burs to expose dentin and grinded with #600 silicon carbide paper. To make sure there was no enamel left, each was observed under an optical microscope. 54 prefabricated zirconium oxide ceramic copings(Lava, 3M ESPE, USA) were assigned into 3 groups ; control, airborne-abraded with $110{\mu}m$ $Al_2O_3$ and scratched with diamond burs at 4 directions. They were cemented with a seating force of 10 ㎏ per tooth, using resin luting cement(Panavia $F^{(R)}$), resin cement(Superbond $C&B^{(R)}$), and resin modified GI cement(Rely X $Luting^{(R)}$). Those were thermocycled at $5^{\circ}C$ and $55^{\circ}C$ for 5000 cycles with a 30 second dwell time, and then shear bond strength was determined in a universal test machine(Model 4200, Instron Co., Canton, USA). The crosshead speed was 1 mm/min. The result was analyzed with one-way analysis of variance(ANOVA) and the Tukey test at a significance level of P<0.05. Results : Superbond $C&B^{(R)}$ at scratching with diamond burs showed the highest shear bond strength than others (p<.05). For Panavia $F^{(R)}$, groups of scratching and sandblasting showed significantly higher shear bond strength than control group(p<.05). For Rely X $Luting^{(R)}$, only between scratching & control group, significantly different shear bond strength was observed(p<.05). Conclusion : Within the limitation of this study, Superbond $C&B^{(R)}$ showed clinically acceptable shear bond between bovine teeth & zirconia ceramics regardless of surface treatments. For the surface treatment, scratching increased shear bond strength. Increase of shear bond strength by sandblasting with $110{\mu}m$ $Al_2O_3$ was not statistically different.

• Korean Chemical Engineering Research
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• v.43 no.4
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• pp.487-494
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• 2005

Nowadays a large amount of wastewater containing metal working fluids and cleaning agents is generated during the cleaning process of parts working in various industries of automobile, machine and metal, and electronics etc. In this study, aqueous or semi-aqueous cleaning wastewater contaminated with soluble or nonsoluble oils was treated using ultrafiltration system. And the membrane permeability flux and performance of oil-water separation (or COD removal efficiency) of the ultrafiltration system employing PAN as its membrane material were measured at various operating conditions with change of membrane pore sizes and soil concentrations of wastewater and examined their suitability for wastewater treatment contaminated with soluble or insoluble oil. As a result, in case of wastewater contaminated with soluble oil and aqueous or semi-aqueous cleaning agent, the membrane permeability increased rapidly even though COD removal efficiency was almost constant as 90 or 95％ as the membrane pore size increased from 10 kDa to 100 kDa. However, in case of the wastewater contaminated with nonsoluble oil and aqueous or semi-aqueous cleaning agent, as the membrane pore size increased from 10 kDa to 100 kDa and the soil concentration of wastewater increased, the membrane permeability was reduced rapidly while COD removal efficiency was almost constant. These phenomena explain that since the membrane material is hydrophilic PAN material, it blocks nonsoluble oil and reduces membrane permeability. Thus, it can be concluded that the aqueous or semi-aqueous cleaning solution contaminated with soluble oil can be treated by ultrafiltration system with the membrane of PAN material and its pore size of 100 kDa. Based on these basic experimental results, a pilot plant facility of ultrafiltration system with PAN material and 100 kDa pore size was designed, installed and operated in order to treat and recycle alkaline cleaning solution contaminated with deep drawing oil. As a result of its field application, the ultrafiltration system was able to separate aqueous cleaning solution and soluble oil effectively, and recycle them. Further more, it can increase life span of aqueous cleaning solution 12 times compared with the previous process.

• Journal of Technologic Dentistry
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• v.20 no.1
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• pp.37-49
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• 1998

The specimens used were Ag-25 Pd-15 Cu ternary alloy and Au addition alloy. These alloys were melted and casted by induction electric furnace and centrifugal casting machine in Ar atmosphere. These specimens were solution treated for 2hr at $800^{\circ}C$ and were then quenched into iced water, and aged at $350{\sim}550^{\circ}C$ Age- hardening characteristics of the small Au-containing Ag-Pd-Cu dental alloys were investigated by means of hardness testing. X-ray diffraction and electron microscope observations, electrical resistance, ergy dispersed spectra and electron probe microanalysis. Principal results are as follows : Hardening occured in two stages, i.e., stage I in low temperature and stage II in high temperature regions, during continuous aging. The case of hardening in stage I was due to the formation of the $L1_0$ type face-centered tetragonal PdCu-ordered phase in the grain interior and hardening in stage I was affected by the Cu concentration. In stage II, decomposition of the ${\alpha}$ solid solution to a PdCu ordered phase($L1_0$ type) and an Ag-rich ${\alpha}2$ phase occurred and a discontinuous precipitation occurred at the grain boundary. From the electron microscope study, it was conclued that the cause of age-hardening in this alloy is the precipitation of the PdCu ordered phase, which has AuCu I type face-centered tetragonal structure. Precipetation procedure was ${\alpha}{\to}{\alpha}+{\alpha}_2+PdCu {\to}{\alpha}_1+{\alpha}_2+PdCu$ at Pd/Cu = 1.7 Ag-Pd-Cu alloy is more effective dental alloy as ageing treatment and is suitable to isothermal ageing at $450^{\circ}C$.

• The Journal of Korean Academy of Prosthodontics
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• v.48 no.3
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• pp.194-201
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• 2010

Purpose: The purpose was to compare the marginal fidelity and the fracture resistance of the zirconia crowns according to the various coping designs with different thicknesses and cement types. Materials and methods: Zirconia copings were designed and fabricated with various thicknesses using the CAD/CAM system (Everest, KaVo Dental GmbH, Biberach., Germany). Eighty zirconia copings were divided into 4 groups (Group I: even 0.3 mm thickness, Group II: 0.3 mm thickness on the buccal surface and the buccal half of occlusal surface and the 0.6 mm thickness on the lingual surface and the lingual half of occlusal surface, Group III: even 0.6 mm thickness, Group IV: 0.6 mm thickness on the buccal surface and the buccal half of occlusal surface and the 1.0 mm thickness on the lingual surface and the lingual half of occlusal surface) of 20. By using a putty index, zirconia crowns with the same size and contour were fabricated. Each group was divided into two subgroups by type of cement: Cavitec$^{(R)}$ (Kerr Co, USA) and Panavia-$F^{(R)}$ (Kuraray Medical Inc, Japan). After the cementation of the crowns with a static load compressor, the marginal fidelity of the zirconia crowns were measured at margins on the buccal, lingual, mesial and distal surfaces, using a microscope of microhardness tester (Matsuzawa, MXT-70, Japan, ${\times}100$). The fracture resistance of each crown was measured using a universal testing machine (Z020, Zwick, Germany) at a crosshead speed of 1 mm/min. The results were analyzed statistically by the two-way ANOVA and oneway ANOVA and Duncan's multiple range test at $\alpha$=.05. Results: Group I and III showed the smallest marginal fidelity, while group II demonstrated the largest value in Cavitec$^{(R)}$ subgroup (P<.05). For fracture resistance, group III and IV were significantly higher than group I and II in Cavitec$^{(R)}$ subgroup (P<.05). The fracture resistances of Panavia-$F^{(R)}$ subgroup were not significantly different among the groups (P>.05). Panavia-$F^{(R)}$ subgroup showed significantly higher fracture resistance than Cavitec$^{(R)}$ subgroup in group I and II (P<.05). Conclusion: Within the limitation of this study, considering fracture resistance or marginal fidelity and esthetics, a functional ceramic substructure design of the coping with slim visible surface can be used for esthetic purposes, or a thick invisible surface to support the veneering ceramic can be used depending on the priority.

• Journal of agricultural medicine and community health
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• v.24 no.1
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• pp.145-159
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• 1999

To find the association, between vinyl house work and the prevalence of low back pain, a questionnaire survey was made toward 215 vinyl house farmers and 228 general farmers without vinyl house who are cared by Jungjung Community health Practioners at Soobuk Myun, Damyang-gun, Chollanamdo. 1. Vinyl house farmers were significantly younger in age, higher in educational status higher survival rate of spouse, higher economic state and less cared by medical aid than general farmers. 2. Vinyl house farmers showed shorter career for agricultural work, used modern farming instrument more frequently and worked with sitting position. 3. During unbusy season in general agriculture, vinyl house farmers consumed significantly more time in agricultural work and general activity, but no significant difference of time of the above activity among busy season. 4. During the last spring season when most vinyl house work was performed, vinyl house farmers showed significantly higher prevalence of low back pain than general farmers, but no significant difference of prevalence among the two groups for the last one week. 5. By the simple analysis statistical significant related variables with low back pain was found to be sex(p<0.001), educational status(p<0.05), work posture(p<0.001) and use of modern agricultural machine(p<0.05). 6. By the multiple logistic regression the odds ratio for low back pain among vinyl house farmers were 2.08(95% confidence interval 1.31-3.00) compared to general farmers, the odds ratio among female was 2.35(95% confidence interval 1.24-4.47) to male, the odds ratio among illiterate persons were 2.60(95% confidence interval 1.24-4.47) to high school graduate, and the odds ration among primary school graduate was 2.19(95% confidence interval 1.04-4.47) to high school graduate. In conclusion because vinyl house farmers showed significantly higher rates of low back pain compared to farmers without vinyl house, continuous study to find the true cause of low back pain among vinyl-house farmers and active effort to prevent low back pain are necessary.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.241-251
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• 2010

This study aims at contributing to the restorative dentistry by examining results in the vertical load test of four different low invasive fixed partial dentures. Based on a hypothesis on the right upper first molar is missing, three units of FPDs were made for the second premolar and the second molar abutment. that is, twelve metal dies and FPDs were made for resin bonded FPD and Two Key Bridges and Human Bridge without occlusal rest and Human Bridge with occlusal rest. By using universal test machine, the numerical maximum value were recorded during the vertical load test of each FPDs after the bonding process treated by Maxcem which is resin cement. The failure process and its result of prosthesis were also observed. The maximum load was 7,295 N, 4,729 N, 2,190 N, 3,073 N from groups of resin bonded FPD, Two Key Bridge, Human Bridge without occlusal rest and Human Bridge with occlusal rest respectively. There was a statistical significance among the groups of resin bonded FPD, Two Key Bridge and Human Brides. However, there was no significant difference between Human Bridge without occlusal rest and Human Bridge with occlusal rest. Regarding the failure of prosthesis, the groups of Resin Bonded FPD and Two Key Bridge showed that one of the abutment teeth in the both side of retention part was highly failed earlier than the other one (83.2% and 66.6% respectively). While, Human Bridge without occlusal rest and Human Bridge with occlusal rest showed high percentage of failure in the abutment teeth in the both side of retention part at the same time (91.6% and 58.3% respectively). This study demonstrates that the group of Human Bridges has low resistance to the vertical loads of low invasive FPDs in comparison with the groups of resin bonded FPD and Two Key Bridge. Nevertheless, the maximum occlusal load of the restorative position, resistance to diverse restoration failure, amount of tooth reduction and patients' cooperation should be considered when they are applied in the clinic in order to choose an appropriate restoration for each patient.

• The Journal of Korean Academy of Prosthodontics
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• v.32 no.1
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• pp.37-46
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• 1994

The purpose of this study was to evaluate the effect of various cements on the retention of casting crown and the cement film thickness. To evaluate the retention of crown, thirty maxillary premolars were used and prepared to largely same dimension. According to the routine method, Non-precious metal crowns were made. The teeth and the metal crowns were divided into three groups and cemented under 5kg static pressure. Group I was composed of 10 teeth and 10 metal crowns and was cemented with zinc phohsphste cement. Group II was composed of 10 teeth and 10 metal crowns and was cemented with Panavia-EX cement. Group III was composed of 10 teeth and 10 metal crowns and was cemented with All-Bond & composite resin cement. After 5 days, the cemented specimens were mounted and the failure loads were measured by an Instron Universal Testing Machine. To evaluate the cement film thickness. 5 metal teeth and 5metal crowns from a prepared maxillary premolar were made. Two marks were flawed on the margin part of each surface at 4-surfaces of each specimen(one mark : crown, the other : metal tooth) and were measured the width with SEM photograph(80 sheets) before and after cementation(Panavia-EX, All-Bond cement, & ZPC) was made. Differences of the widths of marks between before and after were measured, and differences from 4-surfaces of a specimen cemented with a cement were measured and calculated. The results were as follows ; 1. There was a statistically significant difference between the failure loads of group III and the others(p<0.05). 2. There was a statistically significant difference between the cement film thickness of group III and the others(p<0.05).