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1 J Dent Hyg Sci Vol.13, No.3, 2013, pp RESEARCH ARTICLE Lithium Disilicate (IPS e.max CAD) 코어와전장도재사이의전단결합강도에관한연구 김기백ㆍ김재홍 고려대학교일반대학원보건과학과치의기공전공 A Study on the Shear Bond Strength of Veneering Ceramics to the Lithium Disilicate (IPS e.max CAD) Core Ki-Baek Kim and Jae-Hong Kim Department of Health Science Specialized in Dental Laboratory Science and Engineering, Graduate School, Korea University, Seoul , Korea The purpose of this study was to investigate the shear bond strength between various commercial all-ceramic system core and veneering ceramics, and evaluate the clinical stability by comparing the conventional metal ceramic system. The test samples were divided into three groups: Ni-Cr alloy (metal bond), yttria-stabilized, tetragonal zirconia polycrystal (Y-TZP) (zirconia bond), lithium disilicate (lithium disilicate bond). The veneering porcelain recommended by the manufacturer for each type of material was fired to the core. After firing, the specimens were subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.50 mm/min until failure. Average shear strengths (mega pascal) were analyzed with a one-way analysis of variance and the Tukey test (α=0.05). The mean shear bond strength±sd in MPa was 44.79±2.31 in the Ni-Cr alloy group, 28.32±4.41 in the Y-TZP group, 15.91±1.39 in the Lithium disilicate group. The ANOVA showed a significant difference among groups (p<0.05). None of the all-ceramic system core and veneering ceramics could attain the high bond strength values of the metal ceramic combination. Key Words: Dental computer-aided design and computer-aided manufacturing, Lithia disilicate, Bond strength, Zirconium oxide 서론 심미적인치아보철치료에대한환자들의요구가높아지면서최근금속도재관에비해심미적이고제작이간단한전부도재관이임상에서널리사용되고있다. 전부도재관은금속도재관에비하여도재가갖는투명성으로인해보다자연치와유사하게표현되는뛰어난심미성과생체친화성, 생체안정성, 화학적안정성, 높은압축강도, 치아와비슷한열팽창계수를갖는등여러가지장점이있어임상치과영역에서관심이집중되고있다 1,2). 더불어 computer-aided design and computer-aided manufacturing (CAD/CAM) 기술의발달은높은기계적강도와생체적합성을갖는전부도재수복물의사용을더욱증가시킬수있는가능성을열어주고있다. CAD/CAM 시스템의발전으로치과기공소를거치지않고당일수복이가능하게되어빠른치료를원하는환자들의높은관심을받고있다. 특히 CEREC system (Sirona Dental system GmbH, Bensheim, Germany) 을이용한전부도재수복물의제작은그과정을단순화시킴으로써효율적일뿐만아니라신뢰할만한결과를보여준다 3). 2006년 Ivoclar Vivadent사 (Amherst, NY, USA) 에서전 Received: June 26, 2013, Revised: August 18, 2013, Accepted: August 21, 2013 ISSN (Print) / ISSN (Online) Correspondence to: Jae-Hong Kim Department of Health Science Specialized in Dental Laboratory Science and Engineering, Graduate School, Korea University, 161, Jeongneung-ro, Seongbuk-gu, Seoul , Korea Tel: , Fax: , noreason07@korea.ac.kr Copyright 2013 by the Korean Society of Dental Hygiene Science This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

2 김기백ㆍ김재홍 : 리튬디실리케이트코어와전장도재사이의전단결합강도에관한연구 부도재보철물에사용되는재료로 lithum disilicate ceramic 을치과시장에선보였다. 오늘날치과의사와환자의요구조건에부합한강도와심미성이우수하기에널리치과보철물로제작되고있다. Lithum disilicate ceramic는 ingot의형태로 press fit (IPS e.max Press; Ivoclar Vivadent, Amherst, NY, USA) 으로전부도재하부구조물로제작되기도하며, block의형태는치과 CAD/CAM system (IPS e.max CAD; Ivoclar Vivadent, Amherst, NY, USA) 을통해절삭하여치과보철물로제작된다 4,5). Block 형태로시판되는 IPS e.max CAD (Ivoclar Vivadent, Schaan, Liechtenstein) 는한번의 CAD/CAM 작업으로제작되므로치과기공소작업과정이없고, 최소삭제량으로치아의교합력에견딜수있는충분한강도를지녔으며, 심미적이고제작과정의간소화로임상에서의활용도가증가되고있다 6). CEREC system으로제작된단일구조전부도재관은공장에서생산된절삭가능형의단일구조세라믹블록을사용하는데, 강화된물리적성질로파절에대한저항성이높지만심미성이떨어지며, 절삭 (milling) 으로만제작되기에정밀한보철수복물의완성도는떨어지게마련이다. 이러한결점을보완하고정밀한보철수복물의완성과인접자연치아와의조화를위해전장도재의축조가필요하다 7). 그리하여치경부나접촉면의최종보철물형태를보완하기위해 IPS e.max CAD Crystall/Add On (Ivoclar Vivadent, Schaan, Liechtenstein) 을사용한다. 전부도재관의코어와전장도재계면의결합실패는임상연구에서많이보고되고있으며, 특히이중구조치과용지르코니아전부도재관은코어는파절되지않고전장도재만떨어져나가는파절양상이대부분인것으로보고되고있고, lithium disilicate의경우코어나전장도재의파절이실패의주원인이었다 8,9). 코어와전장도재간의실패가발생하는원인으로는첫째로, 구조적인미세균열로인해일어난다. 치과용세라믹은구조적으로탄성에너지를흡수하는능력에제한적이기때문에미세균열이있는경우비교적낮은외력에도파절될수있다. 또한코어와전장도재간의상이한열 팽창계수에의해발생되고, 전장도재의 firing shrinkage, 열혹은 stress에의해야기되는계면에서의결정입자의변형등이실패의원인이될수있다 10). 따라서전부도재관의장기간의안정적인결과를얻기위해서는전장도재간의결합력이중요하지만아직까지 lithium disilicate로제작된코어와전장도재간의전단결합강도에대한연구는극히드물다. 이에본연구의목적은치과임상분야에서적용되고있는 2종의치과용세라믹코어와전장도재사이의전단결합강도를측정하고, 전통적인금속도재관의결합강도결과값을토대로상대적비교평가의자료로활용하고자한다. 재료및방법 1. 연구재료 1) 실험재료전부도재관코어재료인반소결된 zirconia block (IPS e.max ZirCAD; Ivoclar Vivadent, Schaan, Liechtenstein) 과 lithium disilicate ceramic block (IPS e.max CAD LT; Ivoclar Vivadent, Schaan, Liechtenstein) 를이용하였다. 금속도재관코어재료인비귀금속합금 Ni-Cr base metal alloy (Bellabond Plus; BEGO, Bremen, Germany) 를사용하였다. 금속도재군 (metal bond, MB) 을대조군으로지정하였고, 실험군은지르코니아군 (zirconia bond, ZB) 과 lithium disilicate군 (lithium disilicate bond, LB) 으로분류하였다 (Table 1). 2) 시편제작 (1) 금속도재관 (MB) 시편제작 1975년 Schmitz와 Schulmeyer 11) 의연구에서사용된시편의모양을참고하여자체제작한실리콘몰드를이용하여가로 5 mm, 세로 5 mm, 높이 13 mm가되도록 pattern resin (GC Corporation, Tokyo, Japan) 으로직사각기둥시편을제작하였다. 이를통상적인방법으로매몰, 소환, 주조하였 Table 1. List of Materials (N=10) Group Material Core Veneer Manufacturer MB Bellabond plus Ni-Cr alloy Vita VM13 BEGO, Bremen, Germany Vita Zahnfabrik, Bad SäCkingen, Germany ZB IPS e.max ZirCAD IPS e.max Ceram A2 Ivoclar Vivadent, Schaan, Liechtenstein LB IPS e.max CAD LT IPS e.max CAD Crystall Add On Ivoclar Vivadent, Schaan, Liechtenstein MB: metal bond, ZB: zirconia bond, LB: lithium disilicate bond. 291

J Dent Hyg Sci Vol. 13, No. 3, 2013 으며, 절단용디스크를사용하여시편을분리시키고절단면을부드럽게다듬은후, 모든시편의표면에 400, 600 grit silicone carbide 연마지 (Buehler Ltd., Lake Bluff, IL, USA) 로균일하게표면을연마하였다.

3 J Dent Hyg Sci Vol. 13, No. 3, 2013 으며, 절단용디스크를사용하여시편을분리시키고절단면을부드럽게다듬은후, 모든시편의표면에 400, 600 grit silicone carbide 연마지 (Buehler Ltd., Lake Bluff, IL, USA) 로균일하게표면을연마하였다. (2) 전부도재관 (ZB, LB) 시편제작금속도재관시편과동일한모양으로직사각기둥시편을제작하였다. ZB군은블록의수축률을고려하여최종소성후가로 5 mm, 세로 5 mm, 높이 13 mm가되도록반소결상태의지르코니아블록을 low speed diamond disc를이용하여절단하였다. 완전소결과정은 CEREC in-lab system (Sirona, Bensheim, Germany) 의전용퍼니스 (in-fire, Sirona) 에서제조사의지시사항에의거하여시행하였다. LB군은 IPS e.max CAD LT block (Ivoclar Vivadent, Schaan, Liechtenstein) 을 CEREC MCXL milling machine (Sirona) 으로작업하여총 10개의 lithium disilicate ceramic core를제작하였다. Milling된 blue stage의도재관을 furnace (P300; Ivoclar Vivadent, Schaan, Liechtenstein) 에서 850 o C로약 30분동안소성하여결정화과정 (crystalization) 을거쳐완성하였다. 완성된전부도재관시편은 400, 600 grit silicon carbide 연마지 (Buehler Ltd.) 를이용하여금속시편과같은형태로맞추었으며, 초음파세척기에서 10분세척후건조하였다. (3) 도재축성시편마다동일한접촉면과크기를갖는도재축성을위해실리콘몰드를제작하여각각시편에전장도재를축성하였다. 금속도재관전장도재는 VITA VM13 (Vita Zahnfabrik, Bad Säckingen, Germany) 을이용하였고, 전부도재관전장도재는지르코니아 (IPS e.max Ceram; Ivoclar Vivadent, Schaan, Liechtenstein), lithium disilicate (IPS e.max CAD Crystall/Add On) 로각각축성하였다. 도재의수축량을감안하여모든시편을약 2회에걸쳐서제조사의소성스케줄에의거하여최종적으로전장도재가가로 4 mm, 세로 5 mm, 높이 4 mm의직사각기둥의형태가되도록조정하였고연마작업으로마무리하였다. 한명의숙련된치과기공사가작업하고, o C 소성온도로제조사의지시에따라소성하였다 (Fig. 1). 2. 연구방법 1) 전단결합강도측정하중이코어와전장도재사이의접착면과동일한방향으로전달되도록전단결합강도측정용지그에고정한뒤, 전단결합강도측정기 universal testing machine (Model 3345; Instron, Canton, MA, USA) 을이용하여 crosshead speed 0.5 mm/min로파절이일어날때까지전단력을가하여최대적용력 (N) 을측정하고다음의식을이용하여전단결합강도 Shear bond strength (MPa) = (MPa) 를계산하였다 (Fig. 2). Maximum applied force (N) Bonded cross-sectional area (mm 2 ) 2) 파절면관찰전단결합강도측정후파절면양상을알아보기위해세라믹의단면을실체현미경 (KH-7700; Hirox, Tokyo, Japan) 을이용하여관찰하였다. 3) 통계분석전단결합강도의평균과표준편차를계산하고, 각군의결합강도간의유의성을검증하기위해 SPSS 12.0 통계처리 Fig. 1. Schematic diagram shows experimental setup and specimen. Fig. 2. Experimental setup and shear bond test in universal testing machine (Model 3345; Instron, Canton, MA, USA). Z: specimen zig, C: core, V: veneer. 292

김기백ㆍ김재홍 : 리튬디실리케이트코어와전장도재사이의전단결합강도에관한연구 프로그램 (SPSS Inc., Chicago, IL, USA) 을사용하여일원분산분석 (one-way ANOVA) 을통해시행하였고, 집단간의차이를다중비교분석의하나인 Tukey's honestly significant difference test 방법을통해사후분석하였다.

67 4 43.11 26.62 15.81 5 45.89 24.15 17.18 6 43.12 31.67 15.36 7 40.17 27.35 16.23 8 45.87 37.77 14.32 9 44.88 28.26 17.22 10 44.97 21.13 16.95 Mean±SD 44.79±2.31 a 28.32±4.41 b 15.91±1.

31 MPa, 지르코니아전부도재관 (ZB) 실험군은 28.32±4.41 MPa, lithium disilicate 전부도재관 (LB) 실험군은 15.91±1.39 MPa로나타났다. 평균전단결합강도는 MB군, ZB군, LB 군순으로컸다. 각실험군전단결합강도에는통계적으로유의한차이가있었다 (p<0.05, Table 3).

4 김기백ㆍ김재홍 : 리튬디실리케이트코어와전장도재사이의전단결합강도에관한연구 프로그램 (SPSS Inc., Chicago, IL, USA) 을사용하여일원분산분석 (one-way ANOVA) 을통해시행하였고, 집단간의차이를다중비교분석의하나인 Tukey's honestly significant difference test 방법을통해사후분석하였다. 제1종오류의수준은 0.05로정하였다. 결과 1. 전단결합강도각실험군의평균전단결합강도와표준편차는 Table 2 와 Table 2. Mean of Fracture Strength and Standard Deviation (MPa) Group MB ZB LB Mean±SD 44.79±2.31 a 28.32±4.41 b 15.91±1.39 b a,b Data with the different letters are significantly different at 0.05 significance level. MB: metal bond, ZB: zirconia bond, LB: lithium disilicate bond. 같다. 금속도재관 (MB) 대조군에서는 44.79±2.31 MPa, 지르코니아전부도재관 (ZB) 실험군은 28.32±4.41 MPa, lithium disilicate 전부도재관 (LB) 실험군은 15.91±1.39 MPa로나타났다. 평균전단결합강도는 MB군, ZB군, LB 군순으로컸다. 각실험군전단결합강도에는통계적으로유의한차이가있었다 (p<0.05, Table 3). 각집단간의유의한차이를본결과, ZB군과 LB군간에만유의한차이를보이지않았고, 나머지집단간에는유의한차이를보였다 (p <0.05). 2. 파절양상 MB 대조군에서는주로접착성파절 (adhesive failure) 양상이관찰되었으며, ZB와 LB 실험군에서는혼합형파절 (mixed failure) 의양상을보였다. 모든실험군에서응집성파절 (cohesive failure) 은발견되지않았다 (Fig. 3). 고찰 환자들의심미성에대한기대와수요가증가함으로써점차귀금속및비귀금속을포함하지않은수복물에대한요구가증가하고있다. 또한최근들어서전부도재수복물의적용범위가넓어지면서전치부를전부도재수복물로수복하거나, 심지어구치부까지수복하는경우가증가하고있고, 이에따라강도가개선된도재수복용재료가등장하고있다 12). 더불어치과 CAD/CAM 기술의발달은높은기계적강도와생체적합성을갖는전부도재관의사용을더욱증가시킬수있는가능성을열어주고있다. 현재사용중인 Table 3. Result of one-way ANOVA Data of Shear Strengths Material Sum of square Mean square Degree of freedom F-ratio p-value Between groups 4, , Within group Sum 4, Fig. 3. Stereoscopic microscope image shows fractured surfaces of specimens. (A) Metal bond group, (B) zirconia bond group, (C) lithium disilicate bond group. 293

5 J Dent Hyg Sci Vol. 13, No. 3, 2013 대표적인전부도재관은열가압성형방법을이용하는유리 - 세라믹의전부도재, 슬립성형을이용한알루미나강화전부도재, 치과 CAD/CAM의지르코니아및 lithium disilicate 계열전부도재수복물등이있다 13). 새로운전부도재관시스템의코어-전장도재의결합강도와실패양상에대한정보는전부도재관의임상적용시내구성을예측하는데도움을준다 14). 이는접착된두가지재료가분리될때까지전단력을가하여최대적용력을횡단면적으로나누어결합력을계산하는것으로, 비교적간단하고결과를빠르게얻을수있는장점이있다. 따라서보다정확한결과를얻기위해서는시편의형태, 하부구조물과전장도재사이의접촉면적, 전단결합강도측정시사용되는응력이접촉면을누를때의속도등을고려한실험설계가중요하다. 금속도재관의경우적절한코어와전장도재의전단결합강도는 25 MPa 이상을적당한결합이라고보며 15), 지르코니아전부도재관은실험장비, 전장도재의열팽창계수차이및표면조건에따라 MPa 7) 로다양하게나타난다고발표하였으며, glass ceramic과 glass infiltrated alumina ceramic의전단결합강도는 MPa이사용가능한전단결합강도라고보고하였다 16). 또한 2005년에 Derand 등 17) 의연구에의하면임상적으로받아들여지는전부도재관의전단결합강도는 MPa 정도로보고하였다. 이를기준으로본연구의결과를살펴보면금속도재관대조군 (MB군) 은 MPa의분포를보였다. 다른여러연구의수치를비교하였을때적정한전단결합강도를나타내었지만, 금속도재간전단결합실험에대한 2011년 Ishibe 등 18) 의연구에의하면하부물질과전장도재간순수한전단력을가하기는어렵다는것을지적했다. 응력은세라믹의말단지점에불연속적인형태로존재하고, 하부물질과세라믹간에열수축계수의부조화에의한계면간잔존응력이존재하게된다고한다. 또한 De melo 등 19) 의연구에서는전단결합강도는합금의조성과열팽창계수, 그리고산화막두께와같은다양한실험요소에의해오차가발생된다고하였기에본실험결과를뒷받침할수있다. 전부도재관실험군 (ZB, LB군 ) 은 MPa, MPa 범위의전단결합강도를보였고, 두실험군모두혼합형파절양상을나타내었다. 이와같은파절양상은 Aboushelib 등 7) 의결과와유사한결과를보였다. 또한 ZB군은임상적으로받아들여지는전단결합강도범위 (20 40 MPa) 내분포를보였으나, LB군은임상허용범위에못미치는경향을나타냈으며통계적으로유의한차이를보이지않았다 (p> 0.05). Lithium disilicate 전부도재관의경우는임상허용최 소전단결합강도결과는발표된바없지만, Dundar 등 16) 의 glass ceramic 결합강도연구결과에비추어볼때임상에서사용하기엔부족한수치를나타내었다. 결합강도에영향을주는인자는하중속도, 응력분산유형, 두께비율, 결합면의길이와넓이등 20) 다양하기때문에실험실에서측정한전단결합강도의절대치를임상적결과로확대해석하기에는다소무리가있으므로, 상대적비교평가의자료로활용되어야할것으로생각된다 21). 또한전단결합강도시험은비교적간단하고결과를빠르게알수있지만, 반면결과를직접추정할수없고, 편차가크다는것을고려해야한다. 본실험에서사용한시편은임상적인치과보철물의형태를반영하지못했으며, 구강내상황을감안하지못한한계점도있다. 좀더유효한결과를얻기위해서는구강내환경을재현한실험연구나임상연구가필요할것으로판단된다. 요약 본연구는심미치과보철물에사용되는지르코니아, lithium disilicate 코어와전장도재사이의전단결합강도를측정하고, 금속도재관을대조군으로설정하여비교하였다. 직사각기둥모양의시편을각각 10개씩제작하여코어와전장도재사이의전단결합강도를측정한후파절면의양상을실체현미경을통해관찰하였다. 제한된조건하에시행된실험을통하여심미보철분야에널리적용되고있는치과용세라믹코어의전단결합강도를확인하였으며, 측정후비교분석된결과는다음과같다. 2종의치과용세라믹코어와전장도재간에전단결합강도는금속도재관의전단결합강도와유의한차이가있었다 (p<0.05). 본실험결과를토대로 ZB군은임상적으로받아들여지는전단결합강도범위내분포를보이지만, LB군은임상허용범위에못미치는결과값을보였다. 금속도재관과달리지르코니아, lithium disilicate 전부도재관은모두혼합형파절양상을보였다. 결론적으로전단결합강도실험에사용된시편이임상적인치과보철물의형태와는달리실험을위한시편의형태로제작되어임상적결과를반영하지못했으며구강내의상황과도다르다는한계점을가지고있다. 추후에는이를보완하여치과보철물과유사한형태의시편을이용한전단결합강도의측정과구강내조건을고려한추가실험이필요하다고생각된다. 294

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untitled J Dent Hyg Sci Vol. 14, No. 1, 2014, pp.29-34 RESEARCH ARTICLE 저온열화현상이지르코니아코어와전장도재의전단결합강도에미치는영향 김기백ㆍ김재홍 고려대학교일반대학원보건과학과치의기공전공 Influence of Low Temperature Degradation on Bond Strength of Yttria-Stabilized