대한치과보철학회지 :Vol. 37, No. 5, 1999 도재와상아질의표면처리가도재의파절강도에미치는영향 서울대학교치과대학치과보철학교실 이신원 이선형 양재호 정헌영 Ⅰ. 서론도재는우수한물리적성질과생체적합성및심미성으로인해치과보철분야에서매우중요한역할을하고있다. 치과용도재는

대한치과보철학회지 :Vol. 37, No. 5, 1999 도재와상아질의표면처리가도재의파절강도에미치는영향 서울대학교치과대학치과보철학교실 이신원 이선형 양재호 정헌영 Ⅰ. 서론도재는우수한물리적성질과생체적합성및심미성으로인해치과보철분야에서매우중요한역할을하고있다. 치과용도재는 1887년 Land에의해도재인레이와도재관의제작법이소개된이래치관수복재료로이용되기시작하였고 41), 1956년금속도재관의제작법이개발되어전치결손부수복에적용되었으나, 금속코아와금속의투시를차단하기위하여사용되는불투명도재로인하여과도한삭제가필요하고, 금속이빛의투과를차단하여자연치와유사한투명도를얻는데어려움이있었다 72). 1965년 McLean이알루미나강화형장석계도재를소개하면서 50) 전치부심미적수복재료로많이사용되었으나제작과정이복잡하고파절저항이약한점이문제점으로대두되어 14,40,51), 그들의심미적인장점에도불구하고임상에서의활용이제한되어, 이를극복하기위한노력이계속되어왔다. 그결과최근에는수종의전부도재관을위한제품들이적합성과심미성, 그리고강화된파절강도등의장점을강조하면서소개되기시작하였다. 현재관심이집중되고있는전부도재관용도재로는 Optec (Jerenic Pentron, Wallingford, Conn), IPS-Empress (Ivoclar AG, Schaan, Liechtenstein), Dicor (Densply, York, PA), In-Ceram (Vita Zahnfabrik, Sackingen, Germany) 등이있다. IPS-Empress system은심미성과변연적합도등에서우수한전부도재관시스템중하나이다. IPS-Empress system은 1990년 Zurich 치과대 학과 Ivoclar사에의하여개발되었는데, 이시스템은결정화된도재를높은온도에서가압 (heat-press) 하여수복물을제작한다 8,22,32,43,44,59). IPS-Empress system은구치부도재관을제작하는경우도재의축조와소성과정이없이도재관의제작이가능하므로제작이용이하고변연적합성이우수한장점을가지고있다 22). 전부도재관의강도에영향을주는요소로는도재의종류, 도재관제작방법, 지대치형성방법등과함께치아와도재관의접착방법이중요하다. 도재의파절저항을개선하기위하여여러가지면에서노력이있었는데, 특히도재와치아의접착에레진시멘트를사용함으로써도재의파절저항성이개선됨이여러선학들에의해보고되었다 61,49,53,36). Grossman과 Nelson은레진시멘트가법랑질, 상아질에접착되어수복물을강화시킨다고보고하였고 26), Eden과 Kacicz 24) 는평균적으로산부식시킨도재를이중경화레진시멘트를이용하여접착시킨경우인산아연시멘트 (ZPC) 로접착된도재관보다 2배의하중에저항을나타낸다고보고하였다. Doering 등 21) 도레진시멘트는산부식과함께 silane 처리한도재에강한결합을형성한다고하였고 7), Holt 등 31) 은레진과도재사이의결합력은레진시멘트의 cohesive strength 보다강하다고하였다. Sorensen 등 67) 은도재의식각과 silane 처리를병행하면도재와레진계면에서의미세누출이없어진다고보고하였다. 따라서, 전부도재관의파절이나실패를피하기위한원칙에레진시멘트를이용하는접착과정이포함되어 658

야한다 5,12). 레진시멘트와상아질과의접착은상아질접착제에의해제공되며, 상아질접착이이루어지면통상적인지대치형성방법을변형시킬수있다는기대를할수있으나, 현재까지는상아질접착제의효율성은증명되지않은상태이다 58). 접착제와수복물의유지를위한기계적방법으로는 diamond bur를이용하여거칠게하는방법, 알루미나분사방법및도재관의내면을불산으로식각하여미세유지구조를얻는방법이있으며 65), 화학적방법으로는도재표면을 silane coupling agent를이용하여처리할수있는데, silane을통하여레진접착제에대한결합력을 20% 가량증가시킬수있었다고보고되고있다 13). 본연구의목적은디스크형태의도재시편과평평한상아질시편을이용하여, 전부도재관접착시의도재내면처리및상아질결합과정이도재의파절강도에미치는효과를알아보고자하였다. Ⅱ. 연구재료및방법 1. 치아시편의제작 (Fig. 1) 치주질환으로발거된대구치 40개를선택하여교합면의해부학적구조들을제거하고육안으로검사하여치질이건전하고미발육된결함 (hypoplastic defects) 이없는지확인하고투과광선으로검사하여균열 (crack) 이없는지확인하였다. 이후치아를 epoxy resin에포매하고연마기 (Struers, Germany) 를이용하여평평한표면이노출되도록 120, 220, 500 grit의 SiC 연마지로단계적으로연마하여지름 30mm, 높이 20mm의원주형태의시편을만들었다. 상아질시편은접착전까지건조되지않도록 100% 상대습도상태에보관하였다. 2. 도재시편의제작 (Fig. 2) 지름 8mm, 두께 1.5mm의디스크형태의도재시편을만들기위해 Veradisc (Aalba Dent Inc., U.S.A.) 를이용하여 8mm 지름의디스크를만들고, inlay wax(shofu Inc., Japan) 를첨가하여납형을만든후, 이납형을실리콘인상재 (Zerosil & Labosil, Drev-Dentamid-GmbH, Germany) 로복제하였다. 이때납형은주입선까지포함시켜제작하였다. 실리콘주형에연화된 wax 를흘려넣어기본납형을복제하였다. 이렇게해서복제된 40개의납형을 IPS-Empress ring base 위에 5개씩부착하였다. 이후제조회사의지시대로매몰, 소환, 압출성형, 매몰재제거과정을거쳐소성된도재시편을제작하였다. 이때도재시편제작을위해사용된재료는착색법 (staining technique) 에사용되는미리압축되고진공소성된 IPS-Empress Dentin Ingot을사용하였다. 주입선을제거한후 1.5mm의두께를가지도록 220, 400, 600, 1000 grit의 SiC 연마지를이용하여단계적으로연마하여 0.05mm 이내의오차범위내에서정확한두께와평평한면을가진디스크를얻었다. 완성된시편은증류수에서 10분간초음파세척을하고건조시켰다. Fig. 1. Dentin specimen. Fig. 2. Ceramic specimen. 659

3. 접착 (Table 1, 2) 40 개의상아질시편과도재시편을 10 개씩 4개군으로나누어다음과같이상아질과도재의표면처리를달리한후접착하였다. Ⅰ군 : 도재표면을 8% 불산 (All-Bond Porcelain etchant gel, Bisco Inc., U.S.A.) 으로 60초간식각하고 60초동안물로세척한후 40초간건조시켰다. 건조된도재표면을 silane coupling agent인 Monobond-S (Vivadent, Liechtenstein) 로 60 초간처리한후건조시키고접착성레진인 Heliobond (Vivadent, Liechtenstein) 를얇게도포하였다. 상아질표면은 Syntac primer(vivadent, Liechtenstein) 를 15 초간적용한후기름기없는공기로건조시키고, Syntac adhesive(vivadent, Liechtenstein) 를 10초간적용하고건조시킨후 Heliobond를얇게도포하였다. Ⅱ군 : 도재표면에 50μm의알루미나 (Al2O3) 로 10초간분사를실시하였는데, 이때압력은 60 psi 로하고 nozzle과시편사이의거리는 10mm 를유지하였다. 알루미나분사된표면을 5분간초음파세척기로세척한후 Heliobond를도포하였다. 상아질의처리는 Ⅰ군과동일하게하였다. Ⅲ군 : 도재표면은세척한후 Heliobond를도포하였고, 상아질표면은 Ⅰ군과동일하게처리하였다. Ⅳ군 : 도재표면은 Ⅰ군과동일하게처리하였고, 상아질표면은상아질접착처리과정을시행하지않았다. 표면처리된각시편을이중경화레진시멘트인 Variolink Ⅱ(Vivadent, Liechtenstein) 를이용하여접착하였는데, 황색의 base와점도가높은 catalyst를 15초간혼합하여도재표면과상아질표면에고루도포하고정하중기로 2kg의하중을가한상태에서여분의시멘트를깨끗이제거하고, liquid strip (Vivadent, Liechtenstein) 을도포한후측면 4군데와윗면에서각 40초씩광선을조사시켜중합하였다. 파절시험을시행하기전에, 접착된시편을 30분간상온에그대로방치한후 37 의수조에서 24시간보관하였다가, 5 와 55 사이에서 15초의계류시간을갖도록하여 500회의 thermocycling을시행하였다. 4. 파절시험 (Fig. 3) 본실험에서는치아와도재가접착된시편을 Instron universal testing machine의기저부와평 Table 1. Surface treatment procedure of experimental groups Ceramic surface Dentin bonding HF etching GroupⅠ Silane Yes Bonding resin GroupⅡ Sandblasting Bonding resin Yes GroupⅢ Bonding resin Yes HF etching GroupⅣ Silane No Bonding resin Table 2. Composition of materials used for surface treatment Material Composition Tetraethylene glycoldimethacrylate Syntac Primer Maleic acid in watery acetone solution Polyethylene glycoldimethacrylate Syntac Adhesive Glutaraldehyde 50% in watery solution Monobond-S 3-Methacryloxypropyl-trimethoxysilane 1:1 solution of water/ethanol produced with acetic acid ph 4 Heliobond Bis-GMA Triethylene glycol dimethacrylate 660

행하게고정한상태에서 1mm/min 의 cross head speed로압력을가하였다. 압력은도재디스크의중앙에지름이 4mm이고끝이반구형으로만들어진강화된스테인레스스틸 loading stylus를이용하여점진적인하중을가하였다. 하중이가해지는동안연결된 computer에서그래프를얻어도재가완전히파절 (catastrophic fracture) 되는순간의하중을기록하고파절이일어난표면의양상을육안과 SEM을이용하여관찰하였다. 5. 통계처리각군의파절저항을비교분석하기위해서 SPSS/PC+ 통계프로그램에서 One Way ANOVA 를시행하였으며, LSD test를이용하여 0.05의유의수준에서사후검정하였다. Ⅲ. 연구결과 1. 파절저항의기록 (Table 3, 4, 5. Fig. 4) Instron을이용하여도재디스크에압력을가하여도재가파절 (catastrophic fracture) 되는순간의하중값을기록하고, 각군별로평균값을구한결과, Ⅰ 군은 1947.10 N, Ⅱ군은 1677.40 N, Ⅲ군은 1491.60 N, Ⅳ군은 1152.00 N으로 Ⅰ, Ⅱ, Ⅲ, Ⅳ군의순으로높은하중에서도재의파절이일어났다. 상아질접착처리 (dentin bonding procedure) 를행한 Ⅰ, Ⅱ, Ⅲ군중불산식각과 silane 처리를한I군과도재의표면처리를생략한 Ⅲ군사이에는통계적으로유의한차이가나타났고, Ⅰ군이도재의접착면에알루미나분사를시행한 Ⅱ군보다높은파절저항를나타내었으나, 통계적인유의성은없었다. 그리고, 도재에불산식각과 silane 처리를동일하게시행한 Ⅰ군과 Ⅳ군을비교하면, 상아질접착을시행한 Ⅰ군이상아질접착을생략한 Ⅳ군보다통계적으로유의할만한높은하중값을보여, 상아질접착처리가도재의파절강도에상당한영향을보임을알수있었다. Fig. 3. Fracture test using Instron testing machine. Table 3. The mean and standard deviation of the fracture load ( N ) N Mean Std. Deviation Std. Error 95% Confidence Interval for Mean Lower Bound Upper Bound GroupⅠ 10 1947.10 517.82 163.75 1576.68 2317.52 GroupⅡ 10 1677.40 325.96 103.08 1444.22 1920.58 GroupⅢ 10 1491.60 281.76 89.10 1290.04 1693.16 GroupⅣ 10 1152.00 366.11 115.77 890.10 1413.90 Total 40 1567.03 470.57 74.40 1416.53 1717.52 N : Number of specimen Table 4. Analysis of Variance Sum of Squares df Mean Square F Sig. Between Groups 3345743.3 3 1115247.8 7.589.000 Within Groups 5290333.7 36 146953.71 Total 8636077.0 39 661

Table 5. Multiple range test : LSD (P<0.05) Mean 95% Confidence Group (I) Group (J) Difference Std. Error Sig. Interval (I-J) Lower Bound Upper Bound Ⅱ 267.70 171.437.124-77.99 617.39 Ⅰ Ⅲ 455.50* 171.437.012 107.81 803.19 Ⅳ 795.10* 171.437.000 447.41 1142.79 Ⅰ -269.70 171.437.124-617.39 77.99 Ⅱ Ⅲ 185.80 171.437.286-161.89 533.49 Ⅳ 525.40* 171.437.004 177.71 873.09 Ⅰ -455.50* 171.437.012-803.19-107.81 Ⅲ Ⅱ -185.80 171.437.286-533.49 161.89 Ⅳ 339.60 171.437.055-8.09 687.29 Ⅰ -795.10* 171.437.000-1142.79-447.41 Ⅳ Ⅱ -525.40* 171.437.004-873.09-177.71 Ⅲ -339.60 171.437.055-687.29 8.09 * : The mean difference is significant at the.05 level. 2. 파절양상의관찰 Fig. 4. Bar graph showing the mean fracture load. Ⅰ군의경우도재가여러조각으로파절되었으며, 도재의많은부분이상아질에붙어있었고, SEM 사진에서레진이상아질에부분적으로남아있는양상을보였다 (Fig. 5). Ⅱ군에서는약간의도재가상아질에붙어있었고, SEM 사진에서 Ⅰ군과마찬가지로레진이상아질에많이남아있는소견을보이는복합적파절양상을관찰할수있었다 (Fig. 6). Ⅲ군의경우에는도재는상아질에거의남아있지않았고, 레진은대부분상아질에붙어있는, 도재와레진사이의 adhesive failure 양상을보였으며 (Fig. 7), Ⅳ 군에서는도재는상아질에서완전히분리된상태로, Fig. 5. SEM shows dentin surface after fracture test of group Ⅰ specimen. Fig. 6. SEM shows dentin surface after fracture test of group Ⅱ specimen. 662

Fig. 7. SEM shows dentin surface after fracture test of group Ⅲ specimen. Fig. 8. SEM shows dentin surface after fracture test of group Ⅳ specimen. 레진은상아질에서는거의찾아볼수없었고, 대부분상아질과레진사이의 adhesive failure의양상을보였다 (Fig. 8). Ⅳ. 총괄및고안전부도재관의파절저항에영향을미치는요소로는지지물질의탄성계수, 레진접착제의물성, 지대치형성방법, 시멘트층의기포 (void), 표면거칠기, 잔여응력 (residual stress), 도재수복물의두께등이있다 28,61,63). 압축강도의시험은기하학적으로규격화된막대 (geometrically well-defined bar) 의굽힘파절시험과달리표준화된방법이아니다. 많은요소들이결과에영향을미치는데, 시편의두께, 적용되는힘의방향과위치, 그리고 loading stylus의반경등이중요하다 68). 완전한구치부치관의복잡한입체적형태에서는표면처리라는한가지변수에대한영향만을보고자하는정량적인파절강도의비교가어렵기때문에본실험에서는간단한디자인으로도재디스크에 point load를가하여하중치를비교하였다. 본실험과같이 in vitro에서도재디스크를이용하여단순한압력만을가하여파절강도를측정하는것은임상적인상황과는실제로다른점이많다고볼수있으며, 정적시험 (static testing) 으로서는피로스트레스 (fatiguing stress) 하에서의장기적물성에대해해답을제시할수는없다 70). 그러나, 상대적인하중저항능력에대한아이디어를제공할수있을것으 로생각된다. 전부도재관의파절강도는지지구조 (supporting structure) 의탄성계수 (elastic modulus) 에영향을받는데, Scherrer와 de Rijk 61) 의실험에의하면탄성계수가 14GPa인물질에접착된수복물은평균 2800N의하중에저항할수있는반면, 2.94GPa의탄성계수를가지는 substrate에접착된수복물은 478N 정도의하중에저항한다고하였다. 상아질의탄성계수는 12.5GPa정도이지만본실험에서같은군내에서의실험성적이다소변이를보이는것은지지구조인상아질의탄성계수값이일정하지않은데에도그원인이있을것으로생각된다. Tsai 등 70) 은도재의두께가파절강도에미치는영향을연구하는데있어서개개상아질시편의변이요소를제거하기위하여상아질과유사한탄성계수를가지는 epoxy resin을지지구조로이용한바있다. 도재표면을거칠게하는방법에는 diamond bur 로거칠게하는방법, 알루미나를분사하는방법, 그리고불산으로식각하여미세한기계적유지구조를얻는방법등이있다. 이중 diamond bur로도재관의내면을거칠게하는방법은임상적으로는잘사용되지않고, 알루미나분사방법은비교적간편하게할수있는방법으로서 50 μm의 Al2O3 를 0.4MPa의압력으로 nozzle과의거리를 10mm로유지하면서 10초동안가볍게알루미나분사하는것이추천되고있으며 37), 너무과도하게분사하면도재의 chipping이일어날수있다. 본실험에서도도재에알루미나분사를시행한결과, 도재표면처리를하지않 663

은경우에비하여높은파절저항을나타냄을알수있었다. 도재의파절강도는재료자체에존재하는흠의분포에의존한다. 따라서, 도재에대한파절강도의큰변이는제작과정중에생긴초기흠의크기와모양의다양성과관련이있다. 파절강도와중요한흠의크기사이에는다음과같은관계가성립한다. KIC=Yσfc 1/2 여기서 KIC는파절인성 (fracture toughness) 이고 Y는표면스트레스상태및파절선첨부 (crack tip) 의형태에의해결정되는기하변수 (geometric parameter) 이며 σf 는파절강도 (fracture strength), c는흠의크기이다 55). 파절인성은적용된스트레스하에존재하는흠의전파에대한재료의저항으로정의되며, 위의관계에서보면파절강도는중요한흠의크기가줄어들면커짐을알수있다. 본실험에서도재접착면에식각과 silane처리를한실험군이표면처리를하지않은군에비하여유의성있게높은파절강도를보였는데, Thompson과 Anusavice 69) 는레진으로접착한수복물의강도에관여하는요소로산식각에의해표면의흠과표면에너지가변화하고, 레진접착제와레진시멘트가산식각시킨표면에잘스며들게하며, 도재와접착제계면에서물분자를감소시키는것을들었다. 레진으로접착된수복물의파절저항을증진시키는주된기전은불분명하나, 근래연구에의하면첫번째기전만이유의하다고보고있다. 표면의식각은흠의분포를변형시키는방법으로, 매우작은흠을제거하고, 큰흠의크기를감소시키며, 흠의깊이를감소시키는효과를기대하는것이다. 이로인해강도가개선되는것은도재와레진시멘트간에결합이개선되고스트레스전달이향상되기때문이다. 도재의식각이결합강도에미치는영향에관한연구에서 Stangel과 Nathanson 68) 은도재에식각을하고접착을시행한경우모든군에서강도가증가하였다고보고하면서, 도재의식각이결합강도에가장중요한요소라고하였고, 불산의농도에따른미세구조의차이를관찰한결과불산은도재의한상 (phase) 을선택적으로용해하는데유리상 (glass phase) 은 52% 불산에용해되었고, 결정상 (crystalline phase) 은 20% 의불산에용해되었다고보고하였다. 식각시간의영향에대해서는 2.5분간노출 된경우의미세구조는 glassbead로처리한효과를나타내며시간이늘어나면이층이용해되므로전단결합강도는 2.5분간식각한것이 20분식각시보다 2-3 배크다고한바있다. 적절한식각시간은임상적으로 1분정도가추천되고있다 15). Bailey와 Bennett 6) 은도재표면에여러가지산으로표면처리를실시하고관찰한결과불산과황산의시판용액인 Stripit가잔여유리상에침투하여효과가가장우수하였고 ammonium bifluoride는불산보다취급에있어덜위험하다는장점으로관심을모으고있다. Sorensen과 Engelman 66) 도불산으로 3분간식각하면대부분의장석계도재에서결합강도가유의하게증가하였다고하였다. 한편, Lu 와 Harcourt 42) 는도재의파절강도는레진시멘트를이용한접착에의해변형되는데, silane coupling agent가콤포짓트레진과도재의결합에중요한역할을한다고하였다. Silane이결합에기여하는기전은우선콤포짓트레진과도재사이에화학적결합이일어나는것으로설명할수있다. 도재표면에서 silane의가수분해가일어나고 silane과레진사이에공유결합이이루어지며, 도재의높은 silica 함량으로인해 silane이콤포짓트레진과도재표면을화학적으로연결하게하는것이다. 또한, silane이도재표면의젖음 (wetting) 을촉진하여레진시멘트가식각된도재표면의미세구조내로흘러들어가는것을촉진함으로써흠의수와면적을감소시키는것이다. Stangel과 Nathanson도 sialne 처리는 unfilled resin과비교하여식각과상관없이결합강도를증가시킨다고하였다. Hayakawa와 Horie 30) 는도재표면의 OH기와반응하는 silane agent가사용되면콤포짓트레진과도재사이의강한접착을위해불산식각을하지않아도된다고주장하였다. 접착에의한파절저항의증가는 2가지개념으로설명할수있는데, 우선, 법랑질-레진-도재계면에서의강한접착력에의해효율적으로스트레스가전달될수있고, 둘째로, crack의기시를방지하기위해표면을변형시키고레진을도포함으로써강화효과를나타낸다는개념이다. Yoshinari와 De rand 73) 는도재수복물이상아질에레진으로접착된경우파절강도의명백한증가를보이는이유로서도재면을식각시킴으로써흠첨부에서의곡률반경 (radius of curvature) 을증가시키고, 둘째로 silane과레진시멘 664

트로흠첨부를도포함으로써흠첨부의스트레스를감소시키며, 시멘트, 도재관, 치아간의화학적결합으로가장높은인장응력을받는도재의내면을따라생기는변형 (strain) 을감소시키기때문이라고하였다. 도재의흠이레진으로도포되면균열 (crack) 기시의가능성이감소되는데, 흠첨부에서의스트레스는흠깊이의제곱근에비례하고파절선첨부의곡률반경의제곱근에반비례한다 3). Grossman은레진시멘트가치아와도재관의계면을따라스트레스를전달하는능력이있음을보고하였고, 2-dimensional photoelastic study 결과지속적하중 (constant load) 에서는응력이분포되는면적이레진시멘트의경우가 ZPC보다크다고하였다. 시멘트자체의탄성계수도파절강도에영향을미칠수있다. Anusavice와 Hojjatie의유한요소분석연구에따르면높은탄성계수를가지는시멘트를사용하면응력이감소한다고하였으나, 여러연구에의하여 ZPC에비하여낮은탄성계수를가진레진시멘트로접착된수복물에서더높은파절저항이보고되고있다 27,45). 이러한현상에대한설명으로는레진시멘트가스트레스전달에있어 ZPC보다우수하고, 이는아마도 ZPC가표면흠으로침투하는데있어취약하기때문이라고생각된다. 시멘트의피막후경도파절강도에영향을주는요소로고려해야하는데, 몇몇연구에의하면전부도재관하방의시멘트피막후경이가장큰부위는교합면하방에존재하며, 그범위는 100μm에서 160 μm사이라고하였다 18,60). 이들의연구에따르면전부도재관의임상적인파절저항에대한시멘트피막후경의영향은피막후경이 300μm이하에서는무시해도좋을정도라고결론지을수있다. 따라서본실험에서는정하중기를이용하여 2kg의일정한힘으로접착한시멘트피막후경은시편간에동일하고도재의파절강도를비교하는데유의한영향을주지않았다고가정하였다. 본실험의경우모든시편에서파절이일어나는과정에는공통적으로두가지주된파절양상이존재한다. 첫번째파절양상은 Hertzian fracture로서스틸구에의한정점하중 (point loading) 시잘경계지어진원형의파절 (well defined ring and cone fracture) 이일어나는데, 이는 Johnson 등 35) 이설명한 Hertz theory에의한것으로 indentor와실험시편간 에탄성계수의차이를나타내는탄성접촉 (elastic contact) 에의한것이다. 두번째양상의파절은 1mm/min저속하중 (low velocity loading) 에의한굽힘파절 (flexural fracture) 로설명할수있는데, 이것은저속하중으로인해도재가굴곡되어밑면에는인장력이가해지고, 이중굽힘파절시험 (biaxial rupture test specimen) 에서와같은양상이일어나는것이다. 본실험에서는 Empress 도재시편제작시열가압 (heat pressing) 후다른열처리, 즉 layering이나 staining, glazing에해당되는열처리를하지않았다. Dong 등 22) 은다량의백류석 (leucite) 결정과유리기질로구성되는이질성도재인이도재의강도가열가압하는동안에증가되고, 또한최종수복물완성을위해추가되는열처리과정에서더욱더증가되는것으로보고했다. 또한 IPS-Empress에서는추가적인열처리과정에서열팽창계수가낮은유리질내에서열팽창계수가높은백류석이강화되고, 열팽창계수가달라짐으로해서발생되는내부응력이한상의파괴응력또는계면의결합력보다높지않도록냉각되는과정에서냉각속도를조절하여서로분리되지않도록유도하면유리기질내에서접선방향의높은압축응력이발생되고, 열팽창계수가큰백류석결정안으로는방사상인장응력이발생되어초기에는두응력이균형을이루다가최종적으로강도를증가시키는중요한역할을담당하는것으로보고하였다 43,44). 따라서실제구치부도재관의제작시거치게되는열처리과정을시행하면본실험에서얻어진하중값보다높은파절강도를나타낼것이다 1992년, Pröbster 57) 는새로운두가지전부도재관제품 (In-Ceram, IPS-Empress) 을치관의형태로제작하여합착후압축강도를측정해본결과, 강도면에서 In-Ceram이 964.3N, IPS-Empress가 814.1N으로두시스템간의통계학적유의성은없었으며, 단순시편의형태로측정된수치와는달리이둘은임상에서비슷한압축강도를발휘할수있음을암시했다. 이는 IPS-Empress 내면을식각하고 silane처리한후이중경화접착성레진으로접착하여내부에기계적인유지를도모하고내부로부터발생되는균열에대한저항력을높였기때문이었다. 실험결과에서도재내면의처리보다상아질의표면처리즉상아질접착과정 (dentin bonding pro- 665

cedure) 이접착된도재의파절강도에더큰영향을주는것을알수있었다. Groten과 Pröbster의실험 28) 에서도 IPS-Empress 전부도재관을스틸다이에다양한방법으로접착한결과다이에부가적인표면처리를행한경우파절저항이거의 2배가량증가하였다고보고한바있다. 상아질과의결합이이루어지면유지를위해지켜져야하는통상적지대치형성방법의필요성을감소시킬수있다 17). 즉통상적금관에비해적은지대치형성량이필요하고얇은 shoulder, chamfer, 또는 knife edge 형태의마무리선즉도재라미네이트를위한지대치형성과유사한변연으로충분하다고하였으며 34), 이러한변연형태는통상적변연보다우수한심미성을제공할수있을것이다. 또한, 파절되는면이상아질, 접착제, 도재관을통해연속적이므로파절저항이향상된다고생각되고있다. 본실험에서는도재의두께를균일하게 1.5mm로제작하였는데, 임상에서필요한도재의최소한의두께는도재에대한실험성적, 개개환자의최대교합력, 개개치아의저작압, 지대치의탄성계수등의요소에의해결정되어야한다. 임상연구에의하면대구치의평균저작력은 565N이고소구치의경우는 288N으로약 2배정도의차이가있다. 따라서, 실제임상에서구치부의전부도재관을위한지대치형성시균일하게 1.5mm 의삭제를하는것은바람직하지않다고할수있다. 또한, 상아질의탄성계수는상대적으로낮기때문에도재내면에인장응력이높게분포되며따라서자연치에접착되는전부도재관은아말감이나비귀금속합금에의해지지되는경우에비해도재의두께를더부여해야할것이다. 디스크형태의시편을이용한본실험결과, 임상에서 IPS-Empress 전부도재관의파절강도를극대화하기위해서는접착시상아질접착제를반드시사용하고, 도재에는식각과 silane 처리를해야함을확인할수있었다. 그러나, 앞서언급했듯이, 실험상아질시편의탄성계수를표준화하는방법, 자연치를이용한실제적인지대치형태의표준화된형성방법, 구강내환경과비슷한하중및피로조건의부여등이고려되어야하겠고, 접착과정을통하여실제적으로도재관의두께를얼마만큼줄일수있는가에관한정량적인연구도계획되어야할것으로생각된다. Ⅴ. 결론전부도재관접착시상아질접착제사용과도재표면처리에따른도재의파절강도를비교하기위하여, 상아질접착처리를시행하고도재에불산식각과 silane 처리를시행한 Ⅰ군, 상아질접착처리를시행하고도재에알루미나분사를시행한 Ⅱ군, 마찬가지로상아질에대한접착처리를시행하고도재표면처리를생략한 Ⅲ군, 상아질접착처리를생략하고도재에불산식각과 silane 처리를시행한 Ⅳ군으로나누어이중경화레진시멘트로접착하고, 500 회의 thermocycling을시행한후, 도재의파절강도를측정하여다음과같은결과를얻었다. 1. 실험군중, Ⅰ군이가장높은하중에서파절이일어났고, 그다음은 Ⅱ군, Ⅲ군, Ⅳ군의순으로높은파절하중값을나타내었다. 2. 상아질접착과정을동일하게시행한 Ⅰ, Ⅱ, Ⅲ 군의경우, 식각과 silane 처리를한 Ⅰ군이표면처리를하지않은 Ⅲ군에비해유의할만한높은강도를나타냈고 (p<0.05), Ⅱ군과 Ⅲ군사이, Ⅰ군과 Ⅱ군사이에서는통계적으로유의성있는차이는나타내지않았다 (p>0.05). 3. 도재에불산식각과 silane 처리를한 Ⅰ군과 Ⅳ군중, 상아질접착과정을시행한 Ⅰ군이상아질접착과정을하지않은 Ⅳ군보다유의성있게높은파절강도를나타내었다 (p<0.05). 참고문헌 1. Aida M, Hayakawa T. Adhesion of composite to porcelain with various surface conditions. J Prosthet Dent 1995 : 73: 464-70. 2. Anagnostopoulous T, Eliades G. Composion, reactivity and surface interactions of three silane primers. Dent Mater 1993 ; 9 : 182-90. 3. Anusavice KJ, Hojjatie B. Tensile stress in glass ceramic : Effect of flaws and ceramic voids. Int J Prosthodont 1992 ; 5 : 351-8. 4. Anusavice KJ. Recent developments in restorative dental ceramics. J Am Dent Assoc 1993 ; 124 : 72-82. 666

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ABSTRACT THE EFFECT OF SURFACE TREATMENT ON FRACTURE STRENGTH OF DENTAL CERAMICS Shin-Won Lee, D.D.S., Sun-Hyung Lee, D.D.S., M.S.D., Ph.D. Jae-Ho Yang, D.D.S., M.S.D., Ph. D., Hun-Young Chung, D.D.S., M.S.D., Ph.D. Department of prosthodontics, College of Dentistry, Seoul National University The major influencing factors on the strength of all-ceramic crowns are types of dental ceramics, fabrication techniques, methods of abutment preparation and cementation modes of allceramic restorations. Zinc phosphate cement and glass-ionomer cement were used as an early luting media for all-ceramic crowns. Recently many studies have reported that resin cements have more advantages in increasing the fracture strength of restorations comparing with zincphosphate cement and glass-ionomer cement. The purpose of this study is to investigate the effect of etching, silane treatment, sandblasting and dentin bonding agents on fracture strengths of dental ceramics. 40 flat dentin specimens and 40 ceramic discs of 1.5mm thickness and 8mm diameter were fabricated, and divided into 4 groups according to surface treatments. Surface treatments before cementation were as follows. Group Ⅰ : (ceramic) : HF etching - silane treatment - application of bonding resin (dentin) : application of dentin bonding agent Group Ⅱ : (ceramic) : sandblasting - application of bonding resin (dentin) : application of dentin bonding agent Group Ⅲ : (ceramic) : application of bonding resin (dentin) : application of dentin bonding agent Group Ⅳ : (ceramic) : HF etching - silane treatment - application of bonding resin (dentin) : no dentin bonding procedure Dentin specimens and ceramic discs were cemented with dual cure resin cement, and went through thermocycling. Compressive stress es were loaded on the centers of ceramic discs with Instron testing machine, and fracture strengths resista nce for catastrophic fracture were measured The results were as follows. 670

1. The group Ⅰ showed the highest fracture resistance. The next was group Ⅱ. And group Ⅲ, Ⅳ followed. 2. There was a significant difference in the mean value of fracture strengths between group Ⅰ and group Ⅲ (p<0.05), but no significant differences between group Ⅰ and group Ⅱ, and group Ⅱ and group Ⅲ (p>0.05). 3. There was a significant difference in the mean value of fracture strengths between group Ⅰ and group Ⅳ (p<0.05). Key words : All-ceramic restoration, HF etching, Silane, Resin cement, Dentin bonding agent 671