비영리 - S-Space - 서울대학교

저작자표시-비영리-변경금지 2.0 대한민국 이용자는 아래의 조건을 따르는 경우에 한하여 자유롭게 l. 이 저작물을 복제, 배포, 전송, 전시, 공연 및 방송할 수 있습니다.. 다음과 같은 조건을 따라야 합니다:. 저작자표시. 귀하는 원저작자를 표시하여야 합니다.. 비영리. 귀하는 이 저작물을 영리 목적으로 이용할 수 없습니다.. 변경금지. 귀하는 이 저작물을 개작, 변형 또는 가공할 수 없습니다.. l l. 귀하는, 이 저작물의 재이용이나 배포의 경우, 이 저작물에 적용된 이용허락조건 을 명확하게 나타내어야 합니다. 저작권자로부터 별도의 허가를 받으면 이러한 조건들은 적용되지 않습니다.. 저작권법에 따른 이용자의 권리는 위의 내용에 의하여 영향을 받지 않습니다. 이것은 이용허락규약(Legal Code)을 이해하기 쉽게 요약한 것입니다. Disclaimer. 치의학석사학위논문. The effect of resin cement thickness on the flexural strength of ceramic/cement bilayer 레진시멘트 두께가 세라믹/시멘트 중층 시편의 굴곡강도에 미치는 영향. 2015년 2월. 서울대학교 대학원 치의학대학원. 류 예 은. -1-. The effect of resin cement thickness on the flexural strength of ceramic/cement bilayer 지도교수 조 병 훈. 이 논문을 치의학석사 학위논문으로 제출함 2014년 10월. 서울대학교 대학원 치의학과. 류 예 은. 류예은의 석사학위논문을 인준함 2014년 11월 위 원 장. 한 중 석 (인). 부 위 원 장 조 병 훈 (인) 위 원 임 범 순 (인) -2-. 레진시멘트 두께가 세라믹/시멘트 중층 시편의 굴곡강도에 미치는 영향. 류 예 은. 초 록. 1. 목 적 도재수복물은 높은 심미성으로 인해 간접 치아 심미수복 측면에서 널리 사용되고 있다. 하지만 세라믹의 낮은 파절 저항성 때문에 임상가들은 어려움을 겪는다. 도재수복물의 강도에 영향을 미치는 요소에는 세라믹의 물성, 시멘트 접착 과정, 치아 프렙 디자인 등이 있다. 세라믹의 파괴인성 역치 이상의 스트레스 강도가 세라믹에 가해진다면 세라믹은 하중을 받아 균열이 생기고 균열의 끝에서 응력이 집중되며 파절이 일어나게 된다. 도재수복물 의 임상적 성공여부는 세라믹과 치아 경조직간의 합착제의 접착에도 영향을 받을 것이다. 최근 전부도재의 합착에서는 높은 기계적 물성과 합착강도를 보이는 레진시멘트가 선호 되고 있다. 합착 과정에서 사용되는 레진시멘트는 도재수복물과 치아 구조물 사이간의 접착 연결고리가 된다. 도재수복물과 치아 경조직간의 합착과정에 사용되는 레진시멘트 의 두께가 도재수복물과 레진시멘트의 이중층 시편의 강도에 미치는 영향에 대한 연구결 과는 다양하다. 시멘트의 두께가 증가할수록 세라믹/시멘트 이중층의 강도가 약해진다는 연구결과도 있는 반면, 유의할 만한 영향을 미치지 않는다는 결과도 있다.. -3-. 따라서 본 연구의 목적은 레진시멘트의 두께가 세라믹/시멘트 이중층 시편의 굴곡강도에 미치는 영향을 3점 굴곡강도 측정을 통해 알아보는 것이다. 도재수복물이 합착된 후의 구조가 교합력에 의해 굴곡강도가 수복물의 치수측 바닥면에 가해지므로 세라믹/시멘트 이중층시편의 구조와 같은 상황이라고 볼 수 있다. 굴곡강도는 재료의 기계적 물성을 평 가하기 위해 사용되는 지표로서 세라믹의 물성을 평가하기 위한 지표로 널리 사용된다. 치아에 접착된 도재수복물과 합착시멘트의 이중층 구조를 가정하여 하중이 가해졌을 때 합착시멘트의 두께에 따른 세라믹 수복물의 굴곡강도(flexural strength)를 측정하여 레 진시멘트의 두께가 세라믹/시멘트 이중층 시편의 파절에 미치는 영향을 알아보고자 한다.. 2. 방 법 본 연구에서는 CAD/CAM 수복에서 사용되는 IPS Empress CAD ceramic (Ivoclar vivadent)을 각기 다른 두께의 Variolink N (Ivoclar Vivadent)와 합착하여 굴곡강도를 측정하고 파절단면을 관찰하였다. 시멘트 두께를 75 µm 부터 425 µm 까지 총 56개의 세라믹/시멘트 이중층 시편을 제작하였다. 시편의 시멘트 합착면을 지지점이 위치한 하 방으로 향하게 하고 상방으로부터 누르는 3점 굴곡강도를 측정한다. 파절된 시편은 실체 현미경을 이용하여 파절패턴부위를 관찰하였다. 측정된 굴곡강도는 상관분석을 이용해 이변량 상관계수를 구하고, 굴곡강도와 시멘트 두께, 세라믹 두께, 전체 세라믹/시멘트 이중층시편 간의 상관관계를 살펴보았고, 추가로, 두께에 따른 균열의 분포에 대한 평가 는 weibull 통계를 이용하여 분석한다.. 3. 결 과 합착된 시멘트의 두께에 따른 세라믹/시멘트 이중층 시편의 굴곡강도 간에는 유의한 차 이가 없는 것으로 나타났다. 굴곡강도의 평균값은 119.2 Mpa, 표준편차는 41.1 MPa로 -4-. pearson 상관계수는 0.140, p value는 0.303 (p<0.05)을 보여 레진시멘트 두께와 시편 의 굴곡강도 간 유의한 연관성을 보이지 않았다. 세라믹 자체만의 두께와 굴곡강도를 비 교한 통계에서도 0.024의 pearson 상관계수와 0.862의 p value를 보였으며 이중층 시 편의 두께와 굴곡강도를 비교한 통계에서는 0.042의 pearson 상관계수와 0.761의 p value를 보여 레진시멘트 보다 더 낮은 굴곡강도와의 연관성을 보였다. 56개 시편의 Weibull modulus (m)는 3.581 (90% confidence interval, 2.75 - 4.41)로서 비교적 낮은 값을 보였다. 일반적인 세라믹의 m값에 비해 세라믹/시멘트 이중층 시편의 m값이 낮은 것은 시멘트의 합착계면의 조작성 또는 적합성에 문제가 있음을 시사한다. 이는 레진 시멘트의 높은 점도 때문에 균일한 합착이중층을 형성하는 데에 있어 조작성 이 떨어졌기 때문이라 해석된다. Characteristic 강도 값은 132.3MPa (90% confidence interval, 57.7 - 179.8)을 보였다. 실체현미경으로 관찰한 시편의 파절단면 패턴은 특별한 굴곡강도와의 상관성을 보이지 않았다. 위와 같은 결과로 시멘트 두께에 따른 세라믹/시멘트 이중층 시편의 두께에 따른 굴곡강 도의 차이는 유의할 만한 차이를 보이지 않으며 그에 따른 영향은 무시할 만 하다라는 것을 알 수 있었다.. 주요어 : 레진시멘트 두께; 세라믹; 굴곡강도; 이중층시편; Weibull modulus 학 번 : 2011-22437. -5-. Content. 국문 초록 ····················································································· 3. 1. Introduction ·············································································· 7. 2. Material and Methods ································································· 9. 3. Results ·················································································· 11. 4. Discussion ·············································································· 14. 5. Conclusion ············································································· 16. Reference ·················································································· 17. Abstract ···················································································· 19. -6-. Introduction Esthetic is one of major concerns currently when restoration is needed. All-ceramic restoration provides better esthetics than porcelain-fused-to-metal restoration in terms of its better translucency compared to opaque metal-ceramics.1 Multiple of all-ceramic materials and systems have been introduced for clinical use. Many clinical studies showed high success rates for resin-bonded restorations, such as porcelain laminate veneers,2 ceramic inlays and onlays,3 and all-ceramic crowns.4 Still, clinicians have difficulties of fracture of ceramic restorations because of their characteristic of brittleness. There could be many factors affecting the fracture strength of a ceramic restoration, such as tooth preparation design, properties of porcelain, and cementation procedure.5 Resin cements which are critical in cementation procedure link between the tooth structure and ceramic restoration.6 In previously reported studies, the effect of resin-cement film thickness on the clinical fracture strength of ceramic showed no discernable influence.7 Yet, a relatively small(<10%) difference in the characteristic strength was found only between two extreme thickness groups of 26 µm and 297 µm.7 However, Molin and Karlsson demonstrated significantly lower bond strength for the 20 µm resin composite luting agents than 50,100,200 µm films. This study came to results that extremely thin layer of resin cement decreases the strength of ceramic restoration. 8 While increasing thickness of resin cement was reported to reduce the compressive strengths of all-ceramic restoration.9 In the clinical situations, occluding force on the cemented ceramic restorations gives flexural stress on the bottom side of the restoration.. So it can be simulated as the flexural strength (FS) test of. ceramic/cement bilayer. However, the effect of cement thickness is not well established and controversial, especially for the resin cement. Combined with results of studies published before, conclusion could be reached that thick cement layers might exhibit lower strength in some studies.10,11 A study showed that increasing the cement thickness above 70 µm reduced the fracture strength of porcelain jacket crowns.10 The other study addressed that trilayer (glass-ceramic/cement/composite) -7-. specimens with thick cement layer had shown significantly lower reliability and strength.11 As being reviewed, studies on the effect of resin cement thickness show differing results and some results show opposite tendency of increased or decreased fracture strength as resin cement gets thick. Increased consideration of dental ceramics and dental cements as a singular structural unit has resulted in increasing concern about the effect of the stress distribution caused by thickening of the ceramic/cement bilayer on the flexural strength of the bilayer. The clinical situation that resin cement fills the space between the bottom surface of ceramic restoration and dentin, and as a result, provide required resistance to the overlying ceramic restoration can be featured by 3-point bent test for measuring FS of ceramic/cement bilayer with positioning cement layer downward. However, the effect of cement thickness is not well established and controversial, especially for the resin cement. The aim of this study was to see the effect of resin cement thickness that is usually observed in clinical situations on the flexural strength (FS) of all-ceramic restoration using a three-point bend test. In case of ceramic inlays, thickness of 50-300 µm seems to be the volume of layer that might be expected in clinical procedure.9 So the purpose was to evaluate the correlation of cement thickness and FS of rectangular ceramic/cement bilayer specimens 75 µm to 425 µm thick cement layer.. -8-. Material and methods The ceramic block and resin cement used in this study was leucite-reinforced feldspathic porcelain IPS Empress CAD (Ivoclar Vivadent AG, Schaan, Liechtenstein) and a resin cement variolink N (Ivoclar Vivadent AG). Only base of Variolink N was used instead of mixing both base and catalyst together. Meeting the requirements of ISO recommendation, ceramic plates of 2.0 mm x 4.0 mm x 16.0 mm were fabricated by sectioning ceramic blocks using a low-speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL, USA). The ceramic plates were first etched, and silanized in accordance with the manufacturer’s instructions. The ceramic surface was etched with 4.9% hydrofluoric acid (HF, Ceramic etchant, BISCO Inc., Schaumburg, IL, USA) for 60s and thereafter rinsed with water. All surfaces were completely dried with compressed air. Then it was silanized with Ceramic primer (3M ESPE) and once again completely dried with compressed air. Changes in the film thickness were achieved by varying the thickness of plastic spacer sheets. Prior to the cementation, plastic sheet of 50, 100, 200, and 300 µm thickness were placed on two opposite corners of the specimens to obtain the desired resin cement thickness. After applying resin cement on the silanated ceramic surface with assigned spacers, a cover-glass was placed on the cemented ceramic block. Due to the high viscosity of the resin cement, finger pressure was used to assure a correct thickness and distribution of the cement avoiding voids. Since cements reach maximum cure level within 60 seconds of light exposure,12 ceramic plates were light-cured from left side of ceramic block to middle side and finally to right side, each side for 20s, total of 60s. A total of 56 plates of 2.0 mm x 4.0 mm x 16.0 mm out of ceramic blocks were cut using the same diamond saw. All samples were stored in a water bath at temperature of 37℃ for 24 hours before measuring the FS of ceramic/cement bilayer using a three-point bending test. The thickness and width of each ceramic bilayer was measured using a digital micrometer (Mitutoyo, Kawasaki, Japan) before -9-. measuring FS. The specimens were placed on a steel supporter with the span of 12.0mm. An axial compressive load was applied to the middle part of ceramic plates with a crosshead speed of 0.5mm/min until fracture occurs. After fracture test was completed, lateral surface of the fractured specimens were evaluated under a light microscope to assess the real thickness of the resin cement and the character of the fracture. The cement thickness was measured by averaging the thicknesses obtained at three points. Since the cementation was applied by hand pressure, and the cement thickness could not be precisely controlled, a range of resin cement thicknesses were from 75 to 425 µm, based on mean value of the cement thickness measured from 3 points on the ceramic plate. The Weibull distribution, a well known statistical model for describing the strength of brittle materials according to the distribution of crack population, was also used to see the brittle failure characteristics of the ceramic/cement bilayer specimens according to different thickness.13 The variability of strength was estimated by calculation of the Weibull modulus (m). A higher value of m indicates a close grouping of the flexure stress data and σθ is the characteristic stress (MPa).14 The Weibull equation which gives the cumulative probability of failure strength applied stress (σ) is given by: Pf = 1 – e-( σ. /. σθθ)m. - 10 -. as a function of the. Results Table 1. Mean flexural strength, Weibull modulus and characteristic strength with 90% confidence interval of ceramic/cement bilayer specimens with IPS Empress CAD (top surface) facing the loading plunger and the cement layer (bottom surface) facing the supporting arms during testing. Mean flexural strength(MPa). Weibull modulus. Characteristic strength(MPa). 119.23 ± 41.069. 3.581 (2.75 - 4.41). 132.3 (57.7 - 179.8). Figure 1. Plot of the flexural strength of bilayer with increasing thickness of resin cement. - 11 -. Figure 2. Plot of the flexural strength of bilayer with increasing thickness of ceramic. - 12 -. Figure 3. Plot of the flexural strength of bilayer with increasing thickness of ceramic/cement bilayer specimen The mean flexural strength, Weibull modulus, and characteristic strength are summarized in Table 1. The average of flexural strength was 119.2 MPa (119.23 ± 41.069). Correlation between the cement thickness and the FS was not significant (r = 0.140, p = 0.303). The Weibull modulus was 3.581 (90% confidence interval, 2.75 - 4.41). Characteristic strength was 132.3 MPa (90% confidence interval, 57.7 - 179.8). With relation between ceramic thickness and flexural strength, correlation between the cement thickness and the FS was not significant (r = 0.024, p = 0.862). Also with relation between ceramic/cement bilayer thickness and flexural strength, correlation between the cement thickness and the FS was not significant (r = 0.042, p = 0.761). No correlation could be established between the observed fractured specimen patterns. - 13 -. Discussion The average of flexural strength was 119.2 MPa (119.23 ± 41.069). Correlation between the cement thickness and the FS was not significant (r = 0.140, p = 0.303). Characteristic strength is 132.3 MPa (upper limit=57.7, lower limit=179.8). The result suggests that the effect of cement thickness on the flexural strength of ceramic/cement bilayer can be considered negligible. With relation between ceramic thickness and flexural strength, correlation between the cement thickness and the FS was not significant (r = 0.024, p = 0.862). Also with relation between ceramic/cement bilayer thickness and flexural strength, correlation between the cement thickness and the FS was not significant (r = 0.042, p = 0.761). The flexural strength of bilayer specimen was not influenced by the thickness of cement , ceramic, and ceramic/cement bilayer. The Weibull distribution provides information about the probability of failure of a given material at any stress level. It is a well known statistical model for describing the strength of brittle materials according to the distribution of crack population and was also used to see the brittle failure characteristics of the ceramic/cement bilayer specimens according to different thickness. 13 The variability of strength was estimated by calculation of the Weibull modulus (m). A higher value of m indicates a close grouping of the flexure stress data, a more uniform behavior of the material tested and σθ is the characteristic stress (MPa).14 If the m which is an empirical constant related to the properties of flaw size distribution in a material, becomes small, a large crack is more likely to be present and so the mean strength for a given volume decreases.15 The Weibull modulus was 3.581 (90% confidence interval, 2.75 - 4.41). The m value was low compared with general m value of ceramic which is attributed to the low wettability of the resin cement. A wide dispersion in the data, which seems to be inherent to the behavior of the cement itself. High viscosity of resin cements made it difficult to produce uniform specimens and workability reduced. Randomly distributed voids were indeed observed in the cement layer of the fractured - 14 -. ceramic/cement bilayer specimens, which may have contributed to the low Weibull modulus (m) values. Previous study showed that significantly lower strength values were recorded for the thinnest (20 µm) adhesive joint layer.16 Whatever the reasons and background factors may be, this study concluded that an extremely thin layer of resin cement seems to be less resistant to compressive loading and bending stress compared to a thicker layer. Some previous studies showed that a thin film increase the bond strength between opposing surfaces.10,11 Hence the reported results were in conflict with the results of conventional studies.10,11 Similar results for thin layers, however, had been reported for bonding between dentin and resin composites. They attributed their results to water absorption from the dentinal surface and the subsequent reaction between the resin and moist dentin being more pronounced for a thin layer than for a thicker one.17 Our study was not related with tooth structure and not affected by water absorption so this may explain the result that conflict with conventional previous studies. Some other studies showed that the fracture strength was not affected by cement thickness7,8 and combining those reports with the results suggested that the effect of cement film thickness on the flexural strength of the ceramic/cement bilayer structure can be considered negligible. Observation of crack patterns of all specimens did lead to the conclusion that two major fracture types occurred. The first fracture type observed was the Hertzian fracture which is the result of the point loading from the steel support producing a well defined cone fracture. The second type of fracture could be described as a flexural fracture which causes the ceramic plate to bend, places bottom surface in tension.18 No correlation could be established between the flexural strength of ceramic/cement bilayer specimen and observed fracture patterns. Within the dental literature, dental ceramics and dental cements were considered as a singular structural unit for in-vitro mechanical testing.14 IPS Empress CAD was selected as a representative ceramic material in this study because it can be used to fabricate all kinds of restoratives such as - 15 -. inlays, onlays, veneers and crowns . It is used generally in CAD/CAM system and has better property than other feldspathic ceramic that was used before such as MK2. 19. Conclusion The flexural strength of bilayer specimen was not influenced by the thickness of cement, ceramic, and ceramic/cement bilayer.. - 16 -. References 1. 2. Kelly JR. Dental ceramics: Current thinking and trends. 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Dent Mater 2008;24:1141-1147.. - 18 -. Abstract The effect of resin cement thickness on the flexural strength of ceramic/cement bilayer. Rhyu Yae Eun Department of Dentistry School of Dentistry Seoul National University 1. Objective The purpose of this study was to evaluate the effect of resin cement thickness on the flexural strength (FS) of ceramic/cement bilayers using a three-point bending test. 2. Methods Variolink N (Ivoclar Vivadent) was cemented on the ground surface of IPS Empress CAD ceramic (Ivoclar Vivadent). A total of 56 specimens were prepared with resin cement thickness in the range from 75 to 425 µm. The FS was measured using a three-point bending test with the resin cement facing downward. Data were analyzed using correlation coefficient, and the Weibull distribution. 3.Results The FS was 119.2 MPa (119.23 ± 41.069). Correlation between the cement thickness and the FS was - 19 -. not significant (r = 0.140, p =0.303). The Weibull modulus was 3.581 (90% confidence interval, 2.75 - 4.41). Characteristic strength was 132.3 MPa (90% confidence interval, 57.7 - 179.8). No correlation could be established between the observed fractured specimen patterns. Conclusions: There was no significant correlation between the thickness of resin cement and the flexural strength of ceramic/cement bilayer. The small Weibull modulus could be attributed to the low wettability of the resin cement. The effect of cement thickness on the flexural strength of ceramic/cement bilayer was negligible.. Keywords : thickness of resin cement; ceramic; flexural strength; bilayer specimen; Weibull modulus Student Number : 2011-22437. - 20 -.