• The Journal of Advanced Prosthodontics
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• v.8 no.3
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• pp.194-200
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• 2016

PURPOSE. The prospective follow-up aimed to assess the performance of lithium disilicate crowns and clinical reasons of adverse events compromising survival and quality. MATERIALS AND METHODS. 58 patients were treated with 375 heat-pressed monolithic crowns, which were bonded with resin cement. Annual recalls up to five years included a complete dental examination as well as quality assessment using CDA-criteria. Any need for clinical intervention led to higher complication rate and any failure compromised the survival rate. Kaplan-Meier-method was applied to all crowns and a dataset containing one randomly selected crown from each patient. RESULTS. Due to drop-outs, 45 patients (31 females, 14 males) with the average age of 43 years (range = 17-73) who had 327 crowns (176 anterior, 151 posterior; 203 upper jaw, 124 lower jaw) were observed and evaluated for between 4 and 51 months (median = 28). Observation revealed 4 chippings, 3 losses of retention, 3 fractures, 3 secondary caries, 1 endodontic problem, and 1 tooth fracture. Four crowns had to be removed. Survival and complication rate was estimated 98.2% and 5.4% at 24 months, and 96.8% and 7.1% at 48 months. The complication rate was significantly higher for root canal treated teeth (12%, P<.01) at 24 months. At the last observation, over 90% of all crowns showed excellent ratings (CDA-rating Alfa) for color, marginal fit, and caries. CONCLUSION. Heat pressed lithium disilicate crowns showed an excellent performance. Besides a careful luting, dentists should be aware of patients' biological prerequisites (grade of caries, oral hygiene) to reach full success with these crowns.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.5
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• pp.234-239
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• 2002

The spinel was calcined at temperatures in the range of $1000^{\circ}C$ to $1300^{\circ}C$ with $100^{\circ}C$ interval to evaluate the effect of calcination temperature on mechanical properties of spinel-glass dental composites. Although the average particle size of spinel calcined at temperatures from $1000^{\circ}C$ to $1200^{\circ}C$ was within 2.8~3.0 $\mu\textrm{m}$, the spinel calcined at $1300^{\circ}C$ was 4.66 $\mu\textrm{m}$ due to abnormal grain growth. Shrinkage and pore size of the spinel preform decreased and increased, respectively, as calcination temperature increased, indicating that the calcination temperature was significant to the powder compaction and the densification of the composites as a result of particle size and distribution. The optimum strength and the fracture toughness of the composite calcined at $1200^{\circ}C$ were 284$\pm$40 MPa, 2.5$\pm$0.1 MPaㆍ$m^{1/2}$ respectively. Optical experimental results showed that transmittance of the spinel-glass composite in the visible region was twice higher than that of the alumina-glass composite, suggesting that the spinel-glass composites possessed better aesthetic properties for all-ceramic dental crown application.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.3
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• pp.210-215
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• 2012

Some patients with generalized attrition and teeth discoloration may want their anterior teeth to be treated just for esthetic improvement. Ameologenesis imperfecta, however, should be considered for such patients prior to any treatment with thorough clinical and radiographic examination. If a patient is diagnosed with amelogenesis imperfecta, the treatment on anterior teeth just for esthetic purpose is not advisable. In this case, a young man with amelogenesis imperfecta was treated with metal-ceramic restorations. The patient had generalized attrition, teeth discoloration, crown fracture, and cross-bite on the left teeth. The ultimate objective of this treatment was to enhance esthetics and masticatory function. The cross-bite on the left anterior teeth was treated with restorations, whereas the reverse horizontal overlap was maintained on the posterior. The patient was satisfied with the result esthetically and functionally, and the third month recall examination revealed no pathologic changes associated with the treatment.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.2
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• pp.67-84
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• 1991

This study was carried out to investiagate the residual stress caused by the mismatch of thermal expansion and the bond failure resistance of alloy-porcelain specimens. The thermal expansions of alloys and porcelains were measured by using a straight push-rod dilatometer. Porcelain glass transition temperatures, thermal expansion coefficients, and thermal compatibility indices were derived from length-versus-temperature curves. Strain gauges were used to experimentally determine the Young's moduli of porcelains, the residual stresses of porcelain surface, and tensile bond strengths of the specimens of simulated porcelain metal crown. The obtained results were as follows: 1. The coefficients of thermal expansion for alloys were the minimum of $13.53\mu/^{\circ}C$ and the maximum of $20.11\mu/^{\circ}C$ in the range of $100\sim600^{\circ}C$ and those for porcelains were the minimum of $7.72\mu/^{\circ}C$ and the maximum of $31.24\mu/^{\circ}C$ in the range of $100\sim500^{\circ}C$. 2. The glass transition temperature of porcelains exhibited the same value without my relation to the healing rate, and the thermal disharmony of porcelain and alloy was more affected by porcelains than by the alloys. 3. The Young's moduli of body porcelains were larger than those of opaque porcelains(P<0.01) 4. It seemed that the residual stresses of porcelain surfaces in the porcelainalloy systems were more affected by porcelains than by alleys. 5. The bond strengths of the procelain-base metal alloy systems were larger than those of the porcelain-precious metal alloy systems. The fracture strengths of porcelain surfaces showed significant difference between porcelains (P<0.05).

• Journal of Korean society of Dental Hygiene
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• v.9 no.3
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• pp.248-261
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• 2009

Objective : This study was performed in order to figure out Oral Health Actual Condition in Elementary School Teachers in Deagu area. This study was conducted from March through May 2008. Method : A total of three hundred and ten Elementary School Teachers were surveyed. The collected data were analyzed by Oral Health Actual Condition and cognition, Diet habit or living and one's own intellect health state, Oral disease sign symptoms of percent and 2-test and One-way ANOVA test by using SPSS12.0 Program. Results : 1. The most of result Frequencies of tooth brushing per one day were 3 over 91.0% and Oral Examination, Oral Health Education need. 2. The result of oral disease sign and symptom were hypersensitivity due to cold food(39.0%), halitosis(21.6%), gingival bleeding tendency(21.3), clicking sound on TMJ(18.7%), hypersensitivity due to tooth burshing(17.1%), easy crown fracture and to be fine(10.0%), pain on TMJ or limitation of mouth opening(7.1%). 3. The most of result age a group oral hygiene assistance article age 20 for interdental tooth brushing(46.4%), age 50 over not used interdental tooth brushing 38.5%. 4. The result of sign and symptom and snack following was statistically significant(P<0.05), health of own cognition and Oral health of own cognition was statistically significant(P<0.001). Conclusion : The study of understanded the Subjective Elementary School Teachers Oral Health Actual Condition and Promotion of Oral Health follow up Oral examination and Oral Health Education have to system groping.

• Tunnel and Underground Space
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• v.29 no.6
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• pp.425-438
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• 2019

A scaled model test was performed to evaluate the stability of subway twin tunnels excavated in the sedimentary rocks with subhorizontal bedding planes. The size of studied tunnel was 6.2 m×6.8 m and pillar width was 4 m. The anisotropic model test specimen was manufactured with the modeling materials suitable for in-situ rocks by way of dimensional analysis. Fracture and deformation behaviors of tunnels according to applied loads were investigated through the biaxial compression test. As the load was increased on the model specimen, the first crack occurred in the middle part of the pillar across twin tunnels and the gradual fractures progressed at crown and floor of twin tunnels. All the cracks in pillar were generated along the existing bedding planes so that they were found to be the main cause of the pillar failure. In addition, the test results were verified by numerical analysis on the experimental conditions using FLAC ubiquitous joint model. The distribution of plastic regions obtained from numerical analysis were in general agreement with test results, confirming the reliability of the scaled model test conducted in this study.

• Journal of Technologic Dentistry
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• v.38 no.3
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• pp.175-183
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• 2016

Purpose: Observation of Oxide Film Formation and Bonding Strength according to surface treatment of Co-Cr Alloy for porcelain fused to Metal. Methods: metal specimens $0.5mm{\times}25mm{\times}4mm$ in size were made using Co-Cr alloys for porcelain fused to metal crown (Heraenium P, Tae jung Medis). Dental porcelain $0.5mm{\times}25mm{\times}4mm$ in size was sintered on the metal specimens after changing the etching time, sandblasting condition, and heat treatment temperature. Subsequently, the bonding strength was compared by the three-point flexural strength test using a universal testing machine (UTM) to observe the fracture surface and oxidized layers. Results: With regard to the experimental group treated with acid-etching, Specimen 1 treated for 25 minutes (B-3) showed the highest bonding strength, and Specimen 2 treated only with sandblasting showed the most excellent bonding force at 3.5 bar (C-3). With regard to the experimental group treated with sandblasting at 3.5 bar after acid-etching for 25 minutes, Specimen 3 with heat treatment at $980^{\circ}C$ (D-3) showed the highest bonding strength. Conclusion: The specimen which went through both sandblasting and etching, showed an excellent ceramicmetal bond strength.

• Restorative Dentistry and Endodontics
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• v.38 no.4
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• pp.215-221
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• 2013

Objectives: To determine the retentive strength and failure mode of undercut composite post, glass fiber post and polyethylene fiber post luted with flowable composite resin and resin-cement. Materials and Methods: Coronal parts of 120 primary canine teeth were sectioned and specimens were treated endodontically. The teeth were randomly divided into 6 groups (n = 20). Prepared root canals received intracanal retainers with a short composite post, undercut composite post, glass fiber post luted with flowable resin or resin-cement, and polyethylene fiber post luted with flowable resin or resin-cement. After crown reconstruction, samples were tested for retentive strength and failure mode. Statistical analysis was done with one-way ANOVA and Tukey tests (p < 0.05). Results: There were statistically significant differences between groups (p = 0.001). Mean bond strength in the undercut group was significantly greater than in the short composite post (p = 0.030), and the glass fiber post (p = 0.001) and the polyethylene fiber post group luted with resin-cement (p = 0.008). However, the differences between the undercut group and the groups with flowable composite as the luting agent were not significant (p = 0.068, p = 0.557). Adhesive failure was more frequent in the fiber post groups. Conclusions: Although the composite post with undercutting showed the greatest resistance to dislodgement, fiber posts cemented with flowable composite resin provided acceptable results in terms of retentive strength and fracture mode.

• The Journal of Korea Assosiation for Disability and Oral Health
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• v.12 no.2
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• pp.72-76
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• 2016

Traumatic dental injury (TDI) is a common problem in children and adolescent. The prevalence of dental trauma among children with disability as compared to healthy children. The TDI of an immature permanent tooth can lead to the loss of pulp vitality and arrested root development. Traditionally, the treatment of choice for necrotic immature tooth is apexification, which is induction of hard tissue barrier at the apex to produce more favorable conditions for conventional root canal filling. This case report describes the treatment of a necrotic immature permanent central incisor with complicated crown fracture. The patient had multiple disabilities (cerebral palsy, congenital heart disease, developmental delay, and gait disturbance) and suffered from She was suffered from repetitive traumatic injury. Apexification and resin restoration was performed under general anesthesia, and favorable clinical results were achieved.

• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.187-197
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• 2013

PURPOSE. The purpose of this study was to evaluate various core designs on stress distribution within zirconia crowns. MATERIALS AND METHODS. Three-dimensional finite element models, representing mandibular molars, comprising a prepared tooth, cement layer, zirconia core, and veneer porcelain were designed by computer software. The shoulder (1 mm in width) variations in core were incremental increases of 1 mm, 2 mm and 3 mm in proximal and lingual height, and buccal height respectively. To simulate masticatory force, loads of 280 N were applied from three directions (vertical, at a $45^{\circ}$ angle, and horizontal). To simulate maximum bite force, a load of 700 N was applied vertically to the crowns. Maximum principal stress (MPS) was determined for each model, loading condition, and position. RESULTS. In the maximum bite force simulation test, the MPSs on all crowns observed around the shoulder region and loading points. The compressive stresses were located in the shoulder region of the veneer-zirconia interface and at the occlusal region. In the test simulating masticatory force, the MPS was concentrated around the loading points, and the compressive stresses were located at the 3 mm height lingual shoulder region, when the load was applied horizontally. MPS increased in the shoulder region as the shoulder height increased. CONCLUSION. This study suggested that reinforced shoulder play an essential role in the success of the zirconia restoration, and veneer fracture due to occlusal loading can be prevented by proper core design, such as shoulder.