• The Journal of Advanced Prosthodontics
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• 제5권4호
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• pp.471-478
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• 2013

PURPOSE. The aim of the study was to evaluate the effect of annealing on the nanostructure and hardness of Co-Cr metal ceramic samples that were fabricated with a direct metal laser sintering (DMLS) technique. MATERIALS AND METHODS. Five groups of Co-Cr dental alloy samples were manufactured in a rectangular form measuring $4{\times}2{\times}2$ mm. Samples fabricated by a conventional casting technique (Group I) and prefabricated milling blanks (Group II) were examined as conventional technique groups. The DMLS samples were randomly divided into three groups as not annealed (Group III), annealed in argon atmosphere (Group IV), or annealed in oxygen atmosphere (Group V). The nanostructure was examined with the small-angle X-ray scattering method. The Rockwell hardness test was used to measure the hardness changes in each group, and the means and standard deviations were statistically analyzed by one-way ANOVA for comparison of continuous variables and Tukey's HSD test was used for post hoc analysis. P values of <.05 were accepted as statistically significant. RESULTS. The general nanostructures of the samples were composed of small spherical entities stacked atop one another in dendritic form. All groups also displayed different hardness values depending on the manufacturing technique. The annealing procedure and environment directly affected both the nanostructure and hardness of the Co-Cr alloy. Group III exhibited a non-homogeneous structure and increased hardness ($48.16{\pm}3.02$ HRC) because the annealing process was incomplete and the inner stress was not relieved. Annealing in argon atmosphere of Group IV not only relieved the inner stresses but also decreased the hardness ($27.40{\pm}3.98$ HRC). The results of fitting function presented that Group IV was the most homogeneous product as the minimum bilayer thickness was measured (7.11 ${\AA}$). CONCLUSION. After the manufacturing with DMLS technique, annealing in argon atmosphere is an essential process for Co-Cr metal ceramic substructures. The dentists should be familiar with the materials that are used in clinic for prosthodontics treatments.

• The Journal of Advanced Prosthodontics
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• 제7권4호
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• pp.271-277
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• 2015

PURPOSE. This study was to evaluate the marginal fit of two CAD-CAM anatomic contour zirconia crown systems compared to lithium disilicate glass-ceramic crowns. MATERIALS AND METHODS. Shoulder and deep chamfer margin were formed on each acrylic resin tooth model of a maxillary first premolar. Two CAD-CAM systems (Prettau$^{(R)}$Zirconia and ZENOSTAR$^{(R)}$ZR translucent) and lithium disilicate glass ceramic (IPS e.max$^{(R)}$press) crowns were made (n=16). Each crown was bonded to stone dies with resin cement (Rely X Unicem). Marginal gap and absolute marginal discrepancy of crowns were measured using a light microscope equipped with a digital camera (Leica DFC295) magnified by a factor of 100. Two-way analysis of variance (ANOVA) and post-hoc Tukey's HSD test were conducted to analyze the significance of crown marginal fit regarding the finish line configuration and the fabrication system. RESULTS. The mean marginal gap of lithium disilicate glass ceramic crowns (IPS e.max$^{(R)}$press) was significantly lower than that of the CAD-CAM anatomic contour zirconia crown system (Prettau$^{(R)}$Zirconia) (P<.05). Both fabrication systems and finish line configurations significantly influenced the absolute marginal discrepancy (P<.05). CONCLUSION. The lithium disilicate glass ceramic crown (IPS e.max$^{(R)}$press) had significantly smaller marginal gap than the CAD-CAM anatomic contour zirconia crown system (Prettau$^{(R)}$Zirconia). In terms of absolute marginal discrepancy, the CAD-CAM anatomic contour zirconia crown system (ZENOSTAR$^{(R)}$ZR translucent) had under-extended margin, whereas the CAD-CAM anatomic contour zirconia crown system (Prettau$^{(R)}$Zirconia) and lithium disilicate glass ceramic crowns (IPS e.max$^{(R)}$press) had overextended margins.

• 대한치과보철학회지
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• 제43권4호
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• pp.426-437
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• 2005

Statement of problem : Although zirconium oxide ceramics are more and more commonly used in restorative dentistry, for many clinical applications only limited data can be found in the literature. However it is quite clear that hydrofluoric acid etching is impossible with zirconia ceramics. Therefore, other bonding techniques are required in order to lute these materials adhesively. Purpose : The purpose or this study was to evaluate the effects of surface treatments on shear bond strengths between two resin cements and a zirconia ceramic. Materials and methods : Experimental industrially manufactured yttrium-oxide-partially-stabilized zirconia ceramic discs (Adens, Korea) were used for this study. The ceramic specimens divided into five experimental groups and a control group (as received). Five surface treatments were studied 1) sandblasting with 110$\mu$m $Al_2O_3$ at 3 bars pressure 13 seconds at a distance of 10 mm, 2) flame-treated with the Silano-Pen for 5 $s/cm^3$, 3) grinding with a diamond bur. 4) sandblasting + Silano-Pen treatment, 5) diamond bur preparation + Silano-Pen treatment. Acrylic plastic tube (5 mm in height and 3 mm in diameter) were filled with composite to fabricate composite cylinders The composite cylinders were bonded to the ceramic specimens with either Superbond C&B or Panavia F resin luting agents. All cemented specimens were tested under shear loading until fracture on universal testing machine at a crosshead speed 1mm/min; the maximum load at fracture was recorded. Sheat bond strength data were analyzed with oneway analysis of variance and Tukey HSD tests (P<.05). Treated ceramic surfaces and fracture surfaces after shear testing were examined morphologically using scanning electron microscope. Results: Ceramic surface treatment with Silano-Pen after sandblasting improved the bond strength of Superbond C&B resin cement. Supevbond C& B resin cement at Silano-Pen aiker sandblasting($27.4{\pm}3.8MPa$) showed statistically higher shear bond strength than the others. Conclusion: Within the limitation of this study, Superbond C& &B resin cement are suitable for cementation of zirconia ceramics and flame-treated with the Silano-Pen after sandblasting is required to enhance the bond strength.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.182-188
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• 2017

이 연구는 수업이 지향해야 하는 가치에 대한 인식을 탐구하여 선행연구에서 밝혀왔던 좋은 수업의 세부 요소 및 특성들과 더불어 좋은 수업의 가치를 지향할 수 있는 수업의 우세 가치 유형을 분석하는 데 그 목적이 있다. 이를 위해 서울 및 수도권에 위치한 대학 유아교육과 재학생 및 졸업생을 대상으로 좋은 수업에 대한 포괄적인 인식과 관점을 객관적으로 지표화한 TPI를 활용하여, 예비 및 현직교사가 인식하는 좋은 수업에 대한 우세 가치 유형을 교차분석 및 일원분산분석과 사후검증(Tukey의 HSD)으로 분석하였다. 연구 결과 고등학교 수업의 우세가치는 학교유형과 관계없이 "양육" 관점으로, 대학교 수업은 "도제"관점으로 나타났다. 고등학교 수업에 관한 연구결과는 "양육"이 우세 관점으로 나타났으며, 국내외 연구 결과와 차이를 보이지 않았다. 그러나, 대학 수업의 경우 영미권에서는 도제 관점을 우세하게 인식하고 있으나 국내 연구에서는 도제 관점이 우세하여 드러나 차이를 보였다. 또한 현직 유아교사가 실습경험 없는 예비교사보다 "도제" 관점을 우세하게 인식하였다. 국내외 연구와 본 연구 결과를 비교 고찰하여 좋은 수업의 가치를 논의하였다. 향후 연구에서는 학교급과 전공을 세분화하여 예비교사 및 현직교사를 대상으로 한 분석이 요구된다.

• 대한치과보철학회지
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• 제42권5호
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• pp.501-513
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• 2004

Purpose : The purpose of this study was to evaluate the effects of etching time on shear bond strength of four resin cements to IPS Empress 2 ceramic. Material and Methods: Forty rectangular shape ceramic specimens ($10{\times}15{\times}3.5mm$ size) were used for this study. The ceramic specimens divided into four groups and were etched with 10% hydrofluoric acid for 0, 10, 30, 60, 180, 300, 420, 600, and 900 seconds respectively. Etched surfaces of ceramic specimens were coated with ceramic adhesive system and bonded with four resin cement (Variolink II, Panavia F, Panavia 21, Super-Bond C&B) using acrylic glass tube. All cemented specimens were tested under shear loading untill fracture on universal testing machine at a crosshead speed 1mm/min: the maximum load at fracture (kg) was recored. Shear bond strengh data were analyzed with oneway analysis of variance and Tukey HSD tests (p<.05). Etched ceramic surfaces (0-, 60-, 300-, and 600-seconds etching period) and fracture surfaces after shear testing were examined mophologically using scanning electron microscopy. Results : Ceramic surface treatment with 10% hydrofluoric acid improved the bond strength of three resin cement except for Super-Bond C&B cement. Variolink II (41.0$\pm$2.4 MPa) resin cement at 300-seconds etching time showed statistically higher shear bond strength than the other resin cements (Panavia F: 28.3$\pm$2.3 MPa, Panavia 21: 21.5$\pm$2.2 MPa, Super-Bond C&B: 16.7$\pm$1.6 MPa). Ceramic surface etched with 10% hydrofluoric acid for 300 seconds showed more retentive surface texture. Conclusion: Within the limitation of this study, Variolink II resin cement are suitable for cementation of Empress 2 all-ceramic restorations and etching with 10% hydrofluoric acid for 180 to 300 seconds is required to enhance the bond strength.

• Restorative Dentistry and Endodontics
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• 제34권1호
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• pp.30-37
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• 2009

본 연구의 목적은 복합레진의 광중합 전 열처리가 복합레진의 일부 물성에 미치는 영향을 평가하는 것이다. 우식이 없는 여든 개의 발거된 치아를 사용하였다. 네 가지 온도의 복합레진, 즉, 냉장 보관되어 있던 $4^{\circ}C$ 복합레진, 상온 $17^{\circ}C$의 복합레진, $Calset^{TM}$를 이용하여 $48^{\circ}C$까지 전열처리한 복합레진, 그리고 $56^{\circ}C$까지 전열처리한 복합레진을 사용하였다. 복합레진의 물성으로서 치질과의 전단결합강도, 미세경도, 그리고 이중결합 전환율을 측정하였다. 법랑질과 상아질에서 공히 $4^{\circ}C$, $17^{\circ}C$, $48^{\circ}C$, 그리고 $56^{\circ}C$의 온도 중에서 $56^{\circ}C$까지 전열처리한 복합레진이 가장 높은 전단결합강도를 보였으며, 복합레진의 온도가 높을수록 더 높은 전단결합강도를 나타내었다. 복합레진의 온도가 높을수록 더 높은 미세경도를 나타내었다. 복합레진의 온도가 높을수록 이중결합의 전환율이 더 높게 나타났다. 제한된 여건에서 행해진 본 연구의 결과를 통하여 볼 때, 냉장고 또는 실온에 보관되어 있던 복합레진을 미리 열처리하면 치질과의 전단결합강도, 복합레진의 미세경도 및 이중결합 전환율이 증가할 것으로 보인다. 따라서 임상에서 복합레진을 사용 시 복합레진의 물성을 향상시키기 위하여 레진을 미리 열처리하는 것을 추천할 수 있겠다.

• The Journal of Advanced Prosthodontics
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• 제6권3호
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• pp.200-206
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• 2014

PURPOSE. This in vitro study investigated the fracture resistance of endodontically treated premolars restored using silorane-or methacrylate-based composite along with or without fiber or nano-ionomer base. MATERIALS AND METHODS. Ninety-six intact maxillary premolars were randomly divided into eight groups (n = 12). G1 (negative control) was the intact teeth. In Groups 2-8, root canal treatment with mesio-occlusodistal preparation was performed. G2 (positive control) was kept unrestored. The other groups were restored using composite resin as follows: G3, methacrylate-based composite (Z250); G4, methacrylate composite (Z250) with polyethylene fiber; G5 and G6, silorane-based composite (Filtek P90) without and with the fiber, respectively; G7 and G8, methacrylate-and silorane-based composite with nano-ionomer base, respectively. After aging period and thermocycling for 1000 cycles, fracture strength was tested and fracture patterns were inspected. The results were analyzed using ANOVA and Tukey HSD tests (${\alpha}$=0.05). RESULTS. Mean fracture resistance for the eight groups (in Newton) were G1: $1200{\pm}169^a$, G2: $360{\pm}93^b$, G3: $632{\pm}196^c$, G4: $692{\pm}195^c$, G5: $917{\pm}159^d$, G6: $1013{\pm}125^{ad}$, G7: $959{\pm}148^d$, G8: $947{\pm}105^d$ (different superscript letters revealed significant difference among groups). Most of the fractures in all the groups were restorable, except Group 3. CONCLUSION. Silorane-based composite revealed significantly higher strength of the restored premolars compared to that of methacrylate one. Fiber insertion demonstrated no additional effect on the strength of both composite restorations; however, it increased the prevalence of restorable fracture of methacrylate-based composite restored teeth. Using nano-ionomer base under methacrylate-based composite had a positive effect on fracture resistance and pattern. Only fiber-reinforced silorane composite restoration resulted in a strength similar to that of the intact teeth.

• 대한치과기공학회지
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• 제33권1호
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• pp.37-45
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• 2011

Purpose: Heat pressed ceramics, used for all ceramic restorations, have the additional advantage of being technically less change through using of the lost-wax technique. Conceptually, combining the ceramic with the clinically proven reinforcing ability of a metal framework would be advantageous; however, cause of mismatching of fusion between ceramics and metal frameworks which from differences of casting temperature and coefficient of thermal expansion, pressed ceramics could not be used with a metal framework. The purpose of this study was to compare shear bond strength of press-to metal ceramic to porcelain fused non precious metal and feldspatic porcelain fused non precious metal. Methods: The 30 metal specimens were casted in a porcelain fused non precious metal nickel-chromium alloy. They were divided into 3 groups by surface treatment and applied ceramic: $125{\mu}m$ aluminium oxide sandblasting and veneered feldspatic porcelain (group FP), $125{\mu}m$ aluminium oxide sandblasting and had press-to-metal ceramic applied (group PC), porcelain bonder (gold bonder) fused on surface of metal specimens and had press-to-metal ceramic applied (group PCG). In each group 10 metal specimens were used. The press-to-metal ceramic applied 20 specimens had ash-free wax pattern applied, the metal-wax complexes invested, and were pressed with heat press ceramic. All specimens were subjected to shear bond strength test at a crosshead speed of 1.0 mm/min. Results: The results of measured in Mean SD and data were analyzed by one-way AVOVA (p= .05) and Tukey HSD test (p= .05).: group FP $16.090{\pm}1.841$ MPa, group PC $12.620{\pm}1.8256$ MPa, group PCG $10.920{\pm}0.9283$, significant differences between all groups (p < .05). Significant differences were found in each between group FP and group PC, group FP and group PCG (p < .05). Conclusion: The shear bond strength of press-to-metal ceramic to porcelain fused non precious metal was described higher in unused gold bonder group than used gold bonder groups.

• 구강회복응용과학지
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• 제29권4호
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• pp.359-365
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• 2013

본 연구는 lithium disilicate glass-ceramic과 상아질 간의 결합력에 대한 임시 수복재와 임시 충전재의 효과를 평가하기 위함이 목적이었다. 60개의 발치된 치아를 자가중합형 레진에 포매한 후 교합1/3 부위를 절단하였고, 무작위로 15개씩 4그룹으로 나누었다. 그런 후 lithium disilicate glass-ceramic을 다음과 같이 그룹으로 나누어 상아질에 접착시켰다: 아무 처리도 하지 않은 그룹(그룹A), ALIKETM (GC America Inc.)를 적용한 그룹(그룹 B), Luxatemp$^{(R)}$ Automix plus (DMG, Germany)를 적용한 그룹(그룹 C), Fermit$^{(R)}$ (Ivoclar Vivadent, Leichtenstein)를 적용한 그룹(그룹 D). 모든 시편들을 24시간 증류수에 담가 보관한 후, 1 mm/min의 crosshead speed로 만능시험기(Zwick 1456 41, Zwick, Germany) 상에서 전단 결합 강도를 측정하였다. 모든 그룹 간에 결합력의 통계학적 유의성은 없었으며, 파절양상은 대부분 시편에서 접착성(adhesive)과 응집성(cohesive)이 복합적으로 보이는 혼합형(mixed type)을 보였다. 본 실험의 제한된 조건 하에서는 임상에서 lithium disilicate glass-ceramic을 상아질에 접착시, 임시 수복재나 임시 충전재의 영향이 그리 크지 않을 것으로 판단되었다.

• 한국수학교육학회지시리즈C:초등수학교육
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• 제22권1호
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• pp.49-64
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• 2019

이 연구는 우리나라 초등예비교사의 수학의 본질 및 수학 학습에 대한 수학적 신념 및 수학적 신념의 범주별 관련성을 알아보는 데 목적을 두었다. 이를 위해 4개 교육대학교 수학교육과에 재학 중인 1, 2, 3, 4학년 초등예비교사 399명(여학생 283명, 남학생 116명)의 수학적 신념에 대한 자료를 수집하였다. 설문조사에 사용된 문항은 2008년에 실시한 TEDS-M의 신념 관련 연구에 사용하였던 설문지를 국문으로 번역하여 사용하였으며 성별, 학년별, 교육대학교별로 나누어 분석하였다. 또한, 수학의 본질에 대한 신념 사이의 상관 관계를 분석 하였다. 먼저 일원분산분석을 통하여 신념이 각 그룹별로 통계적으로 유의미하게 다른지를 살펴보았으며, 그 후 Duncan의 사후 검증 및 Tukey의 HSD 사후 검증을 실시하여 분석하였다. 연구결과, 예비교사들의 수학의 본질에 대한 신념은 수학이 이미 만들어진 결과인 지식과 절차로 보는 것보다는 탐구의 과정이 수학적 본질에 더 가깝다고 생각하고 있는 것으로 드러났다. 수학학습에 대한 신념 측면에서 연구에 참여한 예비교사들은 '교사지시'에 대해서는 교수 행위로 바람직하지 않다고 보는 반면, 학생들의 주도적 학습에 대해서는 바람직한 것으로 보는 경향이 있었다. 초등 예비교사의 수학적 신념의 범주별 관련성에서 수학을 '탐구의 과정'으로 보는 신념과 수학의 학습이 '주도적 학습'이어야 한다는 신념이 통계적으로 유의미하게 관련되어 있고, 수학을 '규칙과 절차'로 보는 신념과 수학의 학습은 '교사 지시'여야 한다는 신념이 통계적으로 유의미하게 관련이 있는 것으로 나타났다.