대한치과보철학회지 :Vol. 41, No. 2, 2003 DLC 표면처리에따른임플랜트지대주나사의풀림현상에관한연구 서울대학교치과대학보철학교실 * 성균관대학교의과대학치과학교실삼성의료원치과진료부보철과 ** 성균관대학교강북삼성병원치과 ***, 한국과학기술연구원박막기술연구센터 **** 곽재영 * 허성주 * 장익태 * 임순호 ** 이종엽 *** 이광렬 **** Ⅰ. 서론가볍고적절하게견고하고마모저항이있으며화학적으로안정적이고생체친화적인물질이존재한다면이는생체대체물질로사용시매우유용할것이다. 의공학적측면에서이러한물질로는타이타늄합금 (Ti6Al4V) 이나알루미나세라믹 (Al203), 콤포지트물질 (TiN coating on graphite) 등이있으며기존재료의물성을증진시키기위하여 Diamond Like Carbon(DLC) 이나 crystalline diamond를코팅하기도한다. 1) 치과분야에서는여러생체대체물질중에서타이타늄을많이사용하고있는데이는생체내에서골과의계면에전기화학적으로 passivated layer를형성하고골과의반응결과가좋기때문이다. 2) 그러나타이타늄의물성은그리강하지않고치태침착등의문제가있기때문에이러한타이타늄을사용할경우표면물성을증진시키기위하여 nitride coating 이나 epoxy coating등을하기도하며, 이는부수적으로 biodegradation을막는역할을하기도한다. 3,4) 하지만 coating은그부위나목적에따라서필요한성질 이다르고각각의목적에따라강하게또는약하게물성을바꾸는것이사용목적에유리할수있다. 그대표적인경우가임플랜트지대주나사의 coating이다. 임플랜트지대주나사의 coating의성질중 3i의 gold coating screw는표면의물성을약하게해서그변형된성질을이용해서지대치나사의풀림현상을방지하고자하였다. 또한 pure gold의낮은마찰계수는지대치나사를조이는데있어약간의회전을더허용하기에초기토크를증대시기는효과를얻고자하였다. 5) 이번실험에서는이러한지대치나사의풀림방지효과를증대시키는논리중에서지대치나사의풀림방지효과가지대치나사의표면물성을저하시켜서물성변화에의한것인지아니면지대치나사의표면마찰계수를낮추어서초기토크를더가하는것이영향을더욱미치는것인지감별하기위하여물성은변하지않으면서마찰계수가낮은물질을지대치나사표면에 coating 하였다. Coating 재료중에서주성분이 carbon이어서생체친화성이뛰어나고강도도뛰어나며표면마찰계수가낮은물질인 이연구는서울대학교발전기금및간접연구경비에서지원되는연구비에의하여수행되었음. 128
Diamond like carbon (DLC) 을이용해서본실험을하였다. 이는표면의변형을최소로하고마찰계수는상당히감소시킨상태에서지대치나사의풀림현상이어떻게다른지알아보고자하는것이다. 이실험에서사용한 DLC 필름은경도와내마모성화학적안정성등에서다이아몬드와유사한특성을갖고있는박막재료이다. 6) 이 DLC 필름은낮은마찰계수와우수한내마모특성을갖고있어치과이외분야에서보면고체윤활박막으로서 hard disk나 VCR head drum의보호막그리고각종 bearing의코팅재료로사용되고있다. 또한 DLC 필름의치과사용시장점은타이타늄이나 316 스테인레스스틸처럼생체친화성이있다는데있다. 6) 20개의 Avana implant와 ASTM titanium grade 3 abutment screw(soomin Synthesis dental materials Co., Seoul, Korea) 를사용한본연구에서는이러한 DLC필름을임플랜트지대치나사에사용시보통의타이타늄지대치나사와비교하여풀림현상이어떻게달라지는지살펴보고자타이타늄지대치나사표면에 DLC필름을코팅한뒤, 코팅하지않은지대치나사와비교하여초기풀림토크를조사하였다. Ⅱ. 연구재료및방법 1. DLC coating 13.56MHz의 r.f. 플라즈마 CVD 방법으로다이아몬드상카본필름을 20개의치과용임플랜트지대치나사부위에코팅하였다. 치과용임플랜트타이타늄지대치나사는일반적인습식세척과정으로세척후코팅부위만이노출되도록설계된 jig에장착하여진공챔버의음극부위에설치하였다. 합성전에시편은 Ar 플라즈마를이용하여 3.5mTorr의압력과바이어스전압 -400V에서 15분동안건식세척하였다. 그후, 다이아몬드상카본필름과임플랜트사이의접착력을증진시키기위해서수소로희석된 silane (10%) 가스를공급하면서바이어스전압 -200V, 압력 20mTorr에서접착력 500nm 두께로중간접착증진층을코팅하였다. 다이아몬드상카본필름은벤젠의증기를탄소원으로사용하여, 합성압력은 10mTorr에서바이어스전압 -500V의조건에서코팅하였다. 필름의두께는 1μm 가되도록하였다 (Fig. 1). 코팅부위는임플랜트지대치나사의나사산과골부위로하였다 (Fig. 2). Fig. 1. DLC layer on the titanium surface Fig. 2. DLC coating area on the implant abutment screw 129
2. Removal torque test Self tapping fixture 20개 (3.75 13mm) 를 10개는대조군으로, 10개는실험군으로나누었다 (Table Ⅰ). 이후나사의첫번째 pitch 까지아크릴릭레진 (Jet Acrylic, Lang Dental MFG. Co., Wheeling, IL, U.S.A.) 에심어서레진블락 (23mm 23mm 30mm) 을만들었다. 이레진블락은실험의편의성과임플랜트의보호를위해서제작하였다. 대조군의지대치나사 (abutment screw) 종류는 ASTM titanium grade 3 abutment screw를사용하였으며실험군은이 screw에 DLC 코팅한것을사용하였다. 이때 screw driver hole은 hexa type을사용하였다. 초기죄임토크는 32N 으로하였으며조임 기구로는 3i사의 torque driver(3i Implant Innovations Inc. FL. U.S.A.) 를사용하였다. 사용한임플랜트 (3.75 13mm) 는 external hexa구조를가지는것으로하였고, 여기에조립되는지대치부위는 UCLA abutment에금속주조한것을가정하여직경 10mm 높이 15mm의치아모형으로타이타늄을밀링제작하여사용하였다 (Fig. 3). 이때임플랜트 fixture와밀링제작한타이타늄지대치구성성분간의 degree of rotation은대조군 10개와실험군 10개모두평균 3.5도정도였다 (Fig. 4). 각각의시편은풀림토크를전자식토크측정기 (Mark-10 Corp, Hicksville, N.Y. U.S.A) 를사용하여 3회반복측정하였다. 실험결과의통계처리는 Windows용 SPSS 8.0 version(spss, Chicago, U.S.A.) 을사용하였다. Fig. 3. Implant-Abutment, screw-abutment assembly Fig. 4. Rotational misfit of implant Table I. Abutment screw used in this study Group Type of abutment screw Coating N Ⅰ ASTM titanium grade 3 abutment screw Diamond Like Carbon coating 10 Ⅱ ASTM titanium grade 3 abutment screw No coating 10 130
Table II. Result of measurement (unit : Ncm) Abutment screw rotation values(32ncm torque) presented as mean ± standard deviation contrast Removal torque DLC coating Removal torque group 1st 2nd 3rd group 1st 2nd 3rd 1 23 26 28 1 24 27.5 26.5 2 23 23 24 2 25.5 23 22 3 32 31 26 3 23.5 24 25 4 32 29 28 4 29.5 28.5 28 5 23 27.5 25.5 5 29 22 24 6 24.5 26.5 28 6 29 25 27 7 30.5 28.5 31 7 26.5 25 23 8 28.5 23.5 29 8 28 28 28.5 9 34 31.5 31.5 9 29.5 27.5 29.5 10 28 27 28 10 33 28 28.5 Mean 27.85 27.35 27.9 27.75 25.85 26.2 ±4.23 ±2.81 ±2.31 ±2.89 ±2.35 ±2.57 27.9±2.31를나타내었다. 실험군과대조군의풀림토크의유의성차이를알아보기위하여모수분석법인 one-way ANOVA와비모수분석법인 Kruskal-Wallis test를시행하였다. DLC 코팅한지대치나사와코팅하지않은지대치나사의비교결과평균풀림토크는코팅하지않은군이약간큰값을보였으나통계적으로유의한차이를보이지않았다 (p>0.05). Fig. 5. Removal torque values in the study Ⅲ. 결과각실험군에서임플랜트를조이는힘은 32N으로하였으며풀림토크 (removal torque) 는 Table Ⅱ에나타내었으며 Fig. 5에이의값을도표로나타내었다. DLC 코팅군에서 3회측정한초기풀림토크의평균과표준편차는각각 27.75±2.89, 25.85±2.35, 26.2±2.57이었고대조군에서는초기 3회측정한풀림토크값은평균 27.85±4.23, 27.35±2.81, Ⅳ. 고찰만성적인나사풀림현상과임플랜트나나사의파절현상은현재까지많이보고되고있다. 7-14) 이중에서나사풀림현상을감소시키기위하여많은제조회사들은나사표면을변형시켜서 preload를증가키는방법을사용한다. 그러나이러한방법은양날의칼과같아서표면의마찰계수가감소하면나사를조일때 preload가증가될수있지만풀리는저항에대해서도문제가생길수가있다. 따라서이번실험은이러한방법중에마찰계수를감소시켜 preload를증가시키는방법중에서순금의도포와같이표면의물성이나사보다약한것을사용하는것과순수하게마찰계수를감소시키고결과적으로표면을강하게만든것을비교하여, 표면이강화된마찰계수를감소시킨 131
효과와나사표면의변형에의한풀림현상중에서초기풀림토크에관여하는것이어떠한것인가감별해보고자하였다. CP 타이타늄위에내마모성이뛰어난 DLC 필름을코팅한것의물성을코팅하지않은것과비교하면많은차이가난다. DLC 코팅은단순히마찰계수를감소시키지는않고마찰에대한저항도증가시킨다. 코팅시의내마모특성은 DLC 필름이마모될때까지유지되며 1μm 의두께로 DLC를코팅할경우에도코팅하지않은경우보다마모의양상과시간에서많이차이가난다. 순수타이타늄표면은마모실험초기부터표면의손상이시작되고마모가진행된반면에, DLC 표면은 1μm 의 DLC 코팅시 30 시간이지난이후에코팅막이마모되어서타이타늄표면이노출되었다. 15) 마찰계수면에서도코팅하지않은타이타늄표면과 DLC 필름코팅처리된타이타늄표면에서차이를보인다. DLC는습도 50-70% 의대기중에서마찰계수는 0.2 정도를유지하고있어서 0.4 에서 0.6 까지의수치를보이는순수타이타늄표면의마찰계수보다약 50% 이하의값을보여주고있다. 15) 이러한 DLC성질은치과분야에서내마모성이요구되는분야나마찰이문제되는부위에사용할경우유용하리라보여진다. 실제로이를이용한예는심장수술시이용하는 centrifugal blood pump나 ventricular assist device에사용한경우이다. 이는마찰계수는작고마모저항은크며세포생물학적친화성은큰물질인 DLC의성질을이용하여좋은결과를얻은예이다. 1,16) 이번실험에서는이러한우수한내마모성과낮은마찰계수를가진 DLC 를임플랜트지대치나사에코팅하여마찰력이감소되고표면의변형특성이감소된지대치나사가그보다마찰력이큰지대치나사와비교하여초기지대치나사풀림에차이가있는지알아보는실험을하였다. 실험결과지대치나사풀림에서두군은초기 3회의풀림토크를측정했을때비교할만한차이를나타내지않았다. 이는단순히이러한낮은마찰계수와높은마모저항에의해서발생하는 preload는순기능으로만작용하지않으며반대로풀림현상에있어서도유해할수있다는반증을나타낸다. 그러나특이한사항으로는 DLC 코팅된나사의풀림토크값은코팅하지않은타이타 늄나사와비교시통계학적으로차이가없었다는것이다. 이것은표면의마찰계수가낮은지대치나사가쉽게풀릴수있다는사실 5) 을어느정도감안하면마찰계수가낮은나사는어느정도 preload도증가되는효과가있다는사실을반증한다고할수있겠다. 따라서이러한마찰계수의순기능과역기능이어느정도상쇄되어서실제풀림토크값은마찰계수가크고표면의변형이가능한표면처리하지않은타이타늄나사의풀림토크값과도차이가없다고볼수있는것이다. 이는나사풀림의원리가마모에의해서나사의 settling effect가깨지고이어서나사의 tension이상실된후나사가풀리는원리를감안하면단순히초기풀림토크의측정만으로표면이강화된나사가장기적사용면에서유해하다고결론을내릴수는없다는것을암시한다. 따라서추후의실험에서는이러한의문점을해소하기위해마찰계수가작고표면이강화된코팅면과코팅하지않은군과의장기적비교실험도필요하리라생각된다. Ⅴ. 결론이번실험에서는이러한지대치나사의풀림방지효과를증대시키는논리중에서지대치나사의풀림방지효과가지대치나사의표면물성을저하시켜서물성변화에의한것인지아니면지대치나사의표면마찰계수를낮추어서초기토크를더가하는것이영향을미치는것인지감별하기위하여물성은변하지않으면서마찰계수가작은물질을지대치나사표면에 coating 하여실험한군과코팅하지않고실험한군을비교하여다름과같은결론을얻었다. 1. DLC 코팅군에서 3회측정한초기풀림토크의평균과표준편차는각각 27.75±2.89, 25.85± 2.35, 26.2±2.57이었고대조군에서는초기 3회측정한풀림토크값은평균 27.85±4.23, 27.35 ±2.81, 27.9±2.31를나타내었다. 2. 실험군과대조군의풀림토크의유의성차이를알아보기위하여모수분석법인 one-way ANO- VA와비모수분석법인 Kruskal-Wallis test를시행하였다. DLC 코팅한지대치나사와코팅하지않은지대치나사의비교결과평균풀림토크는 132
코팅하지않은군이약간큰값을보였으나통계적으로유의한차이를보이지않았다 (p>0.05). 이상의결과로표면의마찰계수와물성을바꾼코팅나사군과코팅하지않은군을비교할때초기 3회의풀림효과는둘다양호한결과를나타내었고, 지대치나사의변형을고려해보면장기적으로는코팅한군이유리할것으로판단된다. 참고문헌 1. Monties JR, Dion I, Havlik P, Rouais F, Trinkl J, Baquey C. Cora rotary pump for implantable left ventricular assist device : biomaterial aspects. Artif Organs 1997;21:730-734. 2. Thull R. Semiconductive properties of passivated titanium and titanium based hard coatings on metals for implants-an experimental approach. Med Prog Technol 1990;16:225-234. 3. Gil FJ, Solano E, Campos A, Boccio F, Saez I, Alfonso MV, Planell JA. Improvement of the friction behavior of NiTi orthodontic archwires by nitrogen diffusion. Biomed Mater Eng 1988;8(5-6):335-342. 4. Kim H, Johnson JW. Corrosion of stainless steel, nickel-titanium, coated nickel-titanium, and titanium orthodontic wires. Angle Orthod 1999;69:39-44. 5. Martin WC, Woody RD, Miller BH, Miller AW, Implant abutment screw rotations and preloads for four different screw materials and surfaces. J Prosthet Dent 2001;86:24-32. 6. Tang L, Tsai C, Gerberich WW, Kruckeberg L, Kania DR. Biocompatibility of chemicalvapour-deposited diamond. Biomaterials 1995;16:483-488. 7. Ekfeldt A, Carlsson GE, Borjesson G. Clinical evaluation of single-tooth restorations supported by osseointegrated implants: a retrospective study. Int J Oral Maxillofac Implants 1994;9:179-83. 8. Jemt T, Laney WR, Harris D, Henry PJ, Krogh PH, Polizzi G. Osseointegrated implants for single tooth replacement: a 1- year report from a multicenter prospective study. Int J Oral Maxillofac Implants 1991;6:29-36. 9. Jemt T, Lekholm U, Grondahl K. 3-year follow-up study of early single implant restorations ad modum Branemark. Int J Periodontics Restorative Dent 1990;10:341-50. 10. Becker W, Becker BE. Replacement of maxillary and mandibular molars with single endosseous implant restorations: a retrospective study. J Prosthet Dent 1995;74:51-5. 11. Henry PJ, Laney WR, Jemt T, Harris D, Krogh PH, Polizzi G. Osseointegrated implants for single-tooth replacement: a prospective 5-year multicenter study. Int J Oral Maxillofac Implants 1996;11: 450-5. 12. Anderson B, Odman P, Carlsson L, Branemark PI. A new Branemark single tooth abutment: handling and early clinical experience. Int J Oral Maxillofac Implants 1992;7:105-11. 13. Engquist B, Nilson H, Astrand P. Singletooth replacement by osseointegrated Branemark implants. A retrospective study of 82 implants. Clin Oral Implants Res 1995;6:238-45. 14. Anderson B, Odman P, Lindvall AM, Lithner B. Single-tooth restorations supported by osseointegrated implants: results and experiences from a prospective study after 2 to 3 years. Int J Oral Maxillofac Implants 1995;10:702-11. 133
15. Kim HW, Koak JY, Lee KR. The study of the wear resistance on Diamond Like Carbon coating on CP Titanium surface. The J Clinical Dent 1999;8:78-81. 16. Yamazaki K, Litwak P, Tagusari O, Mori T, Kono L, Kameneva M, Watach M, Gordon L, Miyagishima M, Tomioka J, Umezu M, Outa E, Antaki JF, Kormos RL, Koyanagi H, Griffith BP. An implantable centrifugal blood pump with a recirculating purge system (Cool-Seal system). Artificial Organs 1998;22(6):466-74. Reprint request to: Seong-Joo Heo, D.D.S., M.S.D., Ph.D. Department of Prosthodontics, College of Dentistry, Seoul National University 28 Yongun-Dong, Chongno-Gu, Seoul 110-749, Korea heosj@plaza.snu.ac.kr 134
ABSTRACT THE STUDY ON THE REMOVAL TORQUE OF THE DIAMOND LIKE CARBON COATED TITANIUM ABUTMENT SCREWS. Jai-young Koak*, D.D.S., M.S.D., Ph.D., Seong-Joo Heo*, D.D.S., M.S.D., Ph.D., Ik-Tae Chang*, D.D.S., M.S.D., Ph.D., Soon-Ho Yim**, D.D.S., M.S.D., Ph.D., Jong-Yeop Lee***, D.D.S., M.S.D., Ph.D., Kwang-Ryeol Lee****, Ph.D. Department of Prosthodontics, Collage of dentistry, Seoul National University* Department of Prosthodontics dentistry, Samsung Medical Center, School of medicine, Sungkyunkwan University** Department of dentistry, Kangbuk Samsung Hospital, Sungkyunkwan University*** Thin film technology research center, Korea Institute of Science and Technology**** Statement of problem : Implant screw loosening remains a problem in implant prosthodontics. Some abutment screws with treated surfaces were introduced to prevent screw loosening and to increase preload. DLC(Diamond Like Carbon) film has similar properties on hardness, wear resistance, chemical stability, biocompatibility as real diamond materials. Purpose : The purpose of this study was to investigate the effect of lubricant layer on abutment screw and to discriminate more effective method between soft lubricant and hard lubricant to prevent screw loosening. Material and method : In this study, 1μm thickness DLC was used as protective, lubricating layer of titanium screws and 3 times removal torque was measured on the abutment screws to investigate the difference in 10 coated and 10 non-coated abutment screws. Results : The results indicated that the implants with DLC coating group were not more resistant to the applied force in screw loosening. At 32Ncm, the 3 times removal torque in DLC group were 27.75±2.89, 25.85±2.35 and 26.2±2.57. The removal torque in no-coated abutment screws were 27.85±4.23, 27.35±2.81 and 27.9±2.31, respectively. Conclusion : The lubricant layer used in this study was Diamond Like Carbon(DLC) and it have a properties of hard and stable layer. The DLC coating layer was hard enough to prevent distortion of screws in the repeated unscrewing procedure in clinical situation. The reduced friction coefficient in hard DLC layer was not effective to prevent screw loosening. Key words : Removal torque, Abutment screw, Diamond Like Carbon, Friction coefficient 135