• 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.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.1
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• pp.7-13
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• 2020

Purpose: This study was to evaluate marginal and internal discrepancy of 3-unit fixed dental prostheses (FDP) fabricated by subtractive manufacturing and additive manufacturing. Materials and methods: 3-unit bridge abutments without the maxillary left second premolar were prepared (reference model) and the reference model scan data was obtained using an intraoral scanner. 3-unit fixed dental prostheses were fabricated in the following three ways: Milled 3-unit FDP (MIL), digital light processing (DLP) 3D printed 3-unit FDP (D3P), stereolithography apparatus (SLA) 3D printed 3-unit FDP (S3P). To evaluate the marginal/internal discrepancy and precision of the prosthesis, scan data were superimposed by the triple-scan protocol and the combinations calculator, respectively. Quantitative and qualitative analysis was performed using root mean square (RMS) value and color difference map in 3D analysis program (Geomagic control X). Statistical analysis was performed using the Kruskal-Wallis test (α=.05), MannWhitney U test and Bonferroni correction (α=.05/3=.017). Results: The marginal discrepancy of S3P group was superior to MIL and D3P groups, and MIL and D3P groups were similar. The D3P and S3P groups showed better internal discrepancy than the MIL group, and there was no significant difference between the D3P and S3P groups. The precision was excellent in the order of MIL, S3P, and D3P groups. Conclusion: Within the limitation of this study, the 3-unit fixed dental prostheses fabricated by additive manufacturing showed better marginal and internal discrepancy than the those of fabricated by subtractive manufacturing, but the precision was poor.

• The Journal of Korean Academy of Prosthodontics
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• v.54 no.3
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• pp.234-238
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• 2016

Purpose: Increasing use of computer aided design-computer aided manufacturing (CAD-CAM) system and number of design software made design of restoration easy and quick. Outcome of restoration has been dependent on dental technician's wax up proficiency, dentists can design restoration for themselves now. This study aims to investigate the outcome of restoration designs, according to handling skill of CAD-CAM design tool. Materials and methods: A patient's mandibular right 1st molar was prepared. After taking impression, stone model was made, scanned the stone model with 3 shape intra-oral scanner, stereolithography (STL) file was extracted. With 3shape dental designer, one dental technician with more than 5 years work experience (designer 0) and three dental technicians with less than 2years work experience (designer 1, 2, 3-group DT) and 4 1st year residents (designer 4, 5, 6, 7-group RT) designed gold crown on the same STL file. Designed crown's MD (mesio-distal) and BL (bucco-lingual) diameter, height of crown, inter-cuspal distance, number of occlusal contact points were compared. Statistical analysis was carried out, test of normality within each group, using independent t-test. Number of contact points were compared, using Wilcoxon signed-rank test. Results: There was no significant difference between group DT and group RT. Number of contact points also resulted in no significant difference. Conclusion: The outcome of each designed crowns showed no statistical differences, in values which can be expressed as numbers. Subjective factors were different. With increasing proficiency in handling designing software, fabrication of restorations according to each designer's occlusal concept can be made easy.

• Journal of Korean Society of Forest Science
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• v.76 no.3
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• pp.193-199
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• 1987

Simple estimating method of rock drilling and blasting work size is necessary to apply as a guidance of general road plan and a cost analysis of mountain forest road construction. For this work study, 11 cycles were divided in 5km route at Hyeonnammeon Yangyang-gun and the mountain slope at every 20m interval was measured. During working days all kind of works concerned on drilling and blasting was investigated in every cycle. Depending on the simple work study results it's work size can bef estimated with high correlation between drilling length in meter and frequency percentage of mountain slope more than 70%. With total drilling length known the machinery hours, drillers and explosive quantify can be estimated by the regression with high correlation. Estimation of drilling and blasting work by mountain slope gradient in road route is proposed like table 5 with estimating value of machinery hour, drillers and explosive in granite gneiss region.

• Journal of Dental Rehabilitation and Applied Science
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• v.30 no.1
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• pp.16-22
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• 2014

Purpose: The purpose of this study was to assess the marginal and mesial fitness of zirconia single copings and 3-unit fixed partial dentures (FPDs) manufactured with an identical model. Materials and Methods: An epoxy model in which the maxillary right 2nd premolar is lost and maxillary 1st premolar and 2nd molar are formed as abutments was manufactured and scanned by using a laser scanner. A ten units of zirconia single copings were manufactured for maxillary 1st premolar and 2nd molar, respectively and the same number of 3-unit FPDs were manufactured. For the measurements of fitness, the manufactured silicone replicas were divided into four parts and the fitness were measured by digital microscope at measurement points (P1, P2, P3, P4 and P5) of each plane. The measured gaps were classified into three categories: marginal gap (MG, P1), axial gap (AG, average of P2 and P3), occlusal gap (OG, average of P4 and P5). Results: The ranges of MG, AG and OG for single copings were 18.47 - 40.54 ${\mu}m$, 39.73 - 73.61 ${\mu}m$ and 116.90 - 134.69 ${\mu}m$, respectively. The ranges of MG, AG and OG for 3-unit FPDs were 45.95 - 87.44 ${\mu}m$, 23.78 - 57.00 ${\mu}m$ and 99.89 - 131.06 ${\mu}m$, respectively. Conclusion: The result of the study shows that the MGs for 3-unit FPDs were higher than those of single copings, though they are within the range of clinical acceptance, indicating that the use of more homogeneous zirconia block and modification of sintering processes are needed to ensure the prevention of increase of gap in 3-unit FPDs.

• Journal of Dental Rehabilitation and Applied Science
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• v.27 no.2
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• pp.149-159
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• 2011

Restoring and replacing teeth with fixed prostheses commonly used in dental practice. Because of improper oral hygiene care and inaccurate laboratory procedure, complication of fixed prostheses was found in the mouth of patient. Although many efforts have been continually made to obtain the data of long term prognosis of fixed prostheses, it was difficult to do it. The purpose of this study was to evaluate the clinical status of fixed prostheses to improve the quality of dental care. In order to assess the clinical status of fixed prostheses, a total of 154 individuals (aged 22-82, 88 women and 66 men loaded with 578 unit of fixed prostheses, and 423 abutments) who visited the Department of Prosthodontics, Pusan National University Hospital, between January 2009 to December 2009 and removed old fixed prostheses were examined. The results of this study were as follows: 1. Length of service of fixed prostheses was $10.3{\pm}05.5$ years (mean), 10.0 years (median). 2. Location of fixed prostheses was found to have statistically significant influence on longevity of fixed prostheses (P<.05). The longevity of fixed prostheses was high in anterior-posterior combination region (mean:13.1, median:13.5) than anterior and posterior region. 3. Longevity of fixed prostheses made of metal was longest (mean:13.3, median:12.3). 4. Number of units in fixed prostheses was found to have no statistically significant influence on longevity of fixed prostheses (P>.05). 5. Condition of opposing dentition was found to have statistically significant influence on longevity of fixed prostheses (P>.05). The fixed prostheses lasted longest when opposed by complete denture (mean:17.1, median:19.7), removable partial denture, fixed prosthesis and natural dentition trailing behind (P<.05) 6. Periodontal disease (37.5%), dental caries (19.0%), defective margin (18.4%) were frequent complications. In 33.1% of the cases, abutment state after removing fixed prostheses was needed to be extracted.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.5
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• pp.528-534
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• 2008

Purpose: Marginal fit is one of the important components for the successful prosthodontic restoration. Poor fitting margin of the restoration causes hypersensitivity, secondary caries, and plaque accumulation, which later result in prosthodontic failure. CAD/CAM zirconia all-ceramic restorations, such as $LAVA^{(R)}$ (3M ESPE, St.Paul, MN) and $EVEREST^{(R)}$ (KaVo Dental GmbH, Biberach, Germany) systems were recently introduced in Korea. It is clinically meaningful to evaluate the changes of the marginal fit of the CAD/CAM zirconia systems before and after build-up. The purposes of this study are to compare the marginal fit of the two CAD/CAM all-ceramic systems with that of the ceramometal restoration, before and after porcelain build-up Material and methods: A maxillary first premolar dentiform tooth was prepared with 2.0 mm occlusal reduction, 1.0 mm axial reduction, chamfer margin, and 6 degree taperness in the axial wall. The prepared dentiform die was duplicated into the metal abutment die. The metal die was placed in the dental study model, and the full arch impressions of the model were made. Twenty four copings of 3 groups which were $LAVA^{(R)}$, $EVEREST^{(R)}$, and ceramometal restorations were fabricated. Each coping was cemented on the metal die with color-mixed Fit-checker $II^{(R)}$ (GC Cor., Tokyo, Japan). The marginal opening of each coping was measured with $Microhiscope^{(R)}$ system (HIROX KH-1000 ING-Plus, Seoul, Korea. X300 magnification). After porcelain build-up, the marginal openings of $LAVA^{(R)}$, $EVEREST^{(R)}$,and ceramometal restorations were also evaluated in the same method. Statistical analysis was done with paired t-test and one-way ANOVA test. Results: In coping states, the mean marginal opening for $EVEREST^{(R)}$ restorations was $52.00{\pm}11.94\;{\mu}m$ for $LAVA^{(R)}$ restorations $56.97{\pm}10.00\;{\mu}m$, and for ceramometal restorations $97.38{\pm}18.54\;{\mu}m$. After porcelain build-up, the mean marginal opening for $EVEREST^{(R)}$ restorations was $61.69{\pm}19.33\;{\mu}m$, for $LAVA^{(R)}$ restorations $70.81{\pm}12.99\;{\mu}m$, and for ceramometal restorations $1115.25{\pm}23.86\;{\mu}m$. Conclusion: 1. $LAVA^{(R)}$ and $EVEREST^{(R)}$ restorations in comparison with ceramometal restorations showed better marginal fit, which had significant differences (P < 0.05) in coping state and also after porcelain build-up . 2. The mean marginal opening values between $LAVA^{(R)}$ and $EVEREST^{(R)}$ restorations did not showed significant differences after porcelain build-up as well as in coping state (P > .05). 3. $EVEREST^{(R)}$, $LAVA^{(R)}$ and ceramometal restorations showed a little increased marginal opening after porcelain build-up, but did not show any statistical significance (P > .05).

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.1
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• pp.82-90
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• 2009

Statement of problem: Recently, as patients' expectation and interest for esthetics are increasing, concerns of esthetic restoration for removable dentures as well as fixed prosthodontics are also increasing. And the color stability of artificial teeth will affect a long term success rate of the denture. But the stain or discoloration of these artificial teeth as well as denture resin has caused esthetic problem. Purpose: This study was designed to evaluate the influence on color stability of artificial teeth when soy sauce, red pepper paste and coffee which many Koreans have eaten were applied. Material and methods: For artificial teeth type(Endura $Anterio^{(R)}$, Physio $Duracross^{(R)}$, Trubyte $Biotone^{(R)}$) selected for the study, 10 specimens each were soaked into individual beakers of soy sauce, red pepper paste, coffee and distilled water. And $L^*$, $a^*$, $b^*$ value were measured for evaluation of the color difference (${\Delta}E^*$) with spectrophotometer on the 1 day, 1 week, 2 weeks, 4 weeks and 8 weeks after immersion. Results: 1. ${\Delta}E^*$ value of artificial teeth which were soaked in soy sauce and coffee was various according to soaking periods. However there was significant difference between Trubyte $Biotone^{(R)}$ and Physio $Duracross^{(R)}$ in red pepper paste regardless of soaking period(P<.05). 2. Except for 8 weeks of Endura $Anterio^{(R)}$, 4 weeks and 8 weeks of Physio $Duracross^{(R)}$, artificial teeth soaked in red pepper paste regardless of the type had significant difference of ${\Delta}E^*$ value compared with other groups (P<.05). 3. $a^*$, $b^*$ value of Endura $Anterio^{(R)}$ and Trubyte $Biotone^{(R)}$ which were soaked in red pepper paste had significant difference compared with the value of other group(P<.05). Conclusion: Red pepper paste had the greatest effect on color difference of artificial tooth. Physio $Duracross^{(R)}$ showed relatively less color difference than Trubyte $Biotone^{(R)}$ and Endura $Anterio^{(R)}$. But as ${\Delta}E^*$ difference were all less than 3.3, these artificial resin teeth seemed appropriate for clinical use.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.1
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• pp.150-156
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• 2009

Objectives : The conventional removable appliance, composed of wires and acrylic resin, had unaesthetic results and poor retention. The flexible denture, as an alternative, presents improved aesthetics with the thin and strong resin retentive area. In addition, it also enhances patients' sensory function as a result of decreased volume of denture base. The flexibility of the flexible denture reduces the possibility of fracture and distributes the masticatory forces transmitted to the abutments and residual bone tissue. This report describes a 10-year-old girl and a 6-year-old boy with oligodontia treated with the flexible dentures as an alternative to conventional removable appliances. Methods : Impression was taken using alginate material and sent to a laboratory with the bite for fabrication of the flexible denture. Prior to try-in, the flexible denture was immersed in water at $90^{\circ}C$ for one minute and cooled. Impinging area of the denture was checked by $Fit-Checker^{(R)}$ and removed and the denture was delivered to the patient. Results : Both patients were satisfied with the flexible dentures, which presented improved retention and aesthetics. Conclusion : For patients with oligodontia, flexible dentures can be considered as a treatment of choice, which may replace the conventional denture.

• The Journal of Korean Academy of Prosthodontics
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• v.55 no.4
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• pp.372-380
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• 2017

This study was conducted to compare the marginal and internal fit of all ceramic crown using the replica technique and the triple-scan protocol. Materials and methods: Twenty zirconia ceramic crowns were fabricated using titanium abutment model. All crowns were divided into two groups of 10 each, depending on the replica technique and the triple-scan protocol. The internal and marginal fit of 10 zirconia ceramic crowns were measured at 17 points for each specimen using the replica technique. The other 10 ceramic crowns were measured using the triple-scan protocol. Statistical analysis was performed by t-test (${\alpha}=.05$). Results: The mean and standard deviation of marginal and internal fit were significantly different between the replica technique ($49.86{\pm}29.69{\mu}m$) and triple-scan protocol ($75.35{\pm}64.73{\mu}m$, P<.001). The mean and standard deviation of internal fit except marginal fit were $58.38{\pm}31.77{\mu}m$ and $64.00{\pm}46.43{\mu}m$, respectively (P>.343). Conclusion: There was a statistically significant difference in the marginal fit measured by the two methods. However, there was no statistically significant difference in the internal fit between the two methods.