J Dent Hyg Sci Vol.14, No.3, 2014, pp.405-410 RESEARCH ARTICLE 도재소성과정이 Ni-Cr 금속도재관의변연및내면적합도에미치는영향 김기백ㆍ김석환 1 ㆍ김재홍 고려대학교보건과학대학보건과학연구소, 1 김천대학교의료경영학과 Effect of Porcelain Firing Process on the Marginal and Internal Fit of Ni-Cr Alloy Metal-Ceramic Crown Ki-Baek Kim, Seok-Hwan Kim 1 and Jae-Hong Kim Institute for Health Science, College of Health Science, Korea University, Seoul 136-703, 1 Department of Medical Management, Gimcheon University, Gimcheon 740-704, Korea The purpose of this study in vitro investigation was to compare the marginal and internal fit of Ni-Cr alloy metal ceramic crown before and after porcelain veneering. Furthermore, this study evaluated whether the influence of the porcelain firing on the precision of fit of dental prostheses. The maxillary right incisor was selected as an abutment for experiments. Ten working models were prepared. Ni-Cr alloy cores appropriate for each abutment were prepared by lost wax technique. The marginal area and four internal areas of the crowns were measured at two stages: before veneering process and after upper porcelain firing. Silicone replica techniques were used. The data were statistically analyzed with the paired t-test (α=0.05). Mean±SD marginal and internal gap were 67.1±23.3 μm for the nickle chrome alloy core group and 74.4±21.9 μm for the metal ceramic crown group. There were statistically significant differences in all investigated areas (p<0.05). Within the limitations of this study, none of the Ni-Cr alloy metal crown values measured after porcelain firing process exceeded 120 μm, which is the clinically acceptable threshold. Key Words: Internal fit, Marginal fit, Ni-Cr alloy, Porcelain firing process 서론 최근심미보철소재 ( 치과용지르코니아, 글라스세라믹 ) 의개발로전부도재관의사용이증가하고있으나, 금속도재관은여전히도재수복물의보편적하부구조로선택되고있다 1). 금속도재관은 1956년 Brecker 2) 에의해서도입된치과용수복물의한종류로, 지대치에적합되는얇은주조금속코핑과융합되는도재층으로구성되어있다. 이러한금속도재관은주조금속코핑의강도와정확한적합성에도재의심미성이결합된보철물로서 3), 도재의내마모성, 내부식성, 생체친화성등의성질과합금의내충격성등을겸비하고있다. 1970년대이전에는금속도재관의코핑으로금합금이선호되었으나, 체적이큰고정성보철물에는적합하지않은낮은강도와탄성계수등물성의한계가드러나면서이를대체할비귀금속합금의사용이증가하였다. 현재금속도재관코핑으로사용되는비귀금속합금은주된금속에따라크게 Ni-Cr, Co-Cr, 티타늄합금으로분류할수있다 4). 금속도재관의제작에사용되는치과용 Ni-Cr 합금은귀금속합금에비해도재소성시가열에의한변형과구강내장착후교합압에의한변형이작기때문에하부구조물인금속코핑의두께를귀금속합금보다얇게할수있는장점이있다. 또한비중이귀금속합금의 1/2 정도로작아동일주조체의제 Received: July 30, 2014, Revised: August 29, 2014, Accepted: August 30, 2014 Correspondence to: Jae-Hong Kim Institute for Health Science, College of Health Science, Korea University, 161, Jeongneung-ro, Seongbuk-gu, Seoul 136-703, Korea Tel: +82-2-940-2700, Fax: +82-2-916-5943, E-mail: noreason07@korea.ac.kr ISSN 1598-4478 (Print) / ISSN 2233-7679 (Online) Copyright 2014 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 (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
J Dent Hyg Sci Vol. 14, No. 3, 2014 작에사용되는금속의양이적으며내마모성및내변색성과고온유동저항성이우수한장점들이있다 5). 도재소성이금속도재관의적합도에미치는영향에대한연구결과는다양하다. Shillingburg 등 6) 은금속도재관의코핑이가열과정에서변연간격이증가한다고보고하였으며, Buchanan 등 7) 은특히산화과정시비귀금속 (Ni-Cr, Co-Cr) 코핑의변연및내면부위에서변형이크다고보고하였다. 도재소성시적합도의변화는대부분산화과정에서나타나며 8), 이는주조및절삭연마과정에서생긴잔류응력이해소되면서생성된다 9). Shokry 등 10) 은 CP-Ti 합금을 computeraided design/computer-aided manufacture (CAD/CAM) 과주조방식으로제작하여비교했을때 CAD/CAM 방식으로제작된금속도재관만이도재소성과정후적합도저하를보인다고하였다. 금속도재관보철물이오랜기간동안성공적으로구강내에서기능하기위해서는우수한변연적합도및내면적합도가필수적이다. 변연적합도의결함은음식물과세균의침투를야기하는데이런것들이축적이되면치주염등을일으킬수있으며 11), 내부간극은수복물의유지에영향을미친다 12). 보철물의변연과내면의우수한적합성은치아우식증의재발과치주질환을감소시키며, 보철물의수명을연장시킬수있다 13). 따라서본연구에서는 Ni-Cr alloy로코어를제작하여변연및내면적합도를측정하고, 코어위에도재를축성하고소성하여금속도재관을완성한후, 변연및내면적합도를측정하여코어의변연및내면적합도를측정하였다. 또한도재를축성하여소성하는과정이 Ni-Cr alloy의변연및내면적합도에영향을미치는지알아보고자한다. 연구대상및방법 1. 연구대상 1) 주모형의제작본연구를위해레진표준치아모형 (AG-3; Frasaco GmbH, Tettnang, Germany) 가운데상악우측중절치를선택하여순면, 설면, 절단부는 1.5 mm, 변연부는 1.0 mm, 360 o chamfer margin, 축면경사도는 6 o 를부여하여삭제하였다. 날카로운모서리가생기지않도록모두둥글게처리하였다. 지대치디자인이완료된파일을토대로티타늄블록을가공하여티타늄의주모형을제작하였다 (Fig. 1). Fig. 1. Titanium master model. 2) 석고지대치모형의제작반복작업으로인한지대치손상을방지하기위해서티타늄지대치모형을복제용 silicone (Deguform; DeguDent- GmbH, Hanau-Wolfgang, Germany) 으로복제하였고, 복제된 silicone mold의내면에치과용초경석고 (GC Fujirock EP; GC Europe N.V., Leuven, Belgium) 를주입하여 10개의초경석고지대치작업모형을제작하였다. 3) Ni-Cr alloy 코어제작 (Ni-Cr alloy core, NCC 그룹 ) 초경석고지대치모형에 die spacer (Space-It; George Taub Products, Jersey City, NJ, USA) 를도포함으로써내면공간을부여하였다. 내면공간은시멘트합착공간의의미이며이를위해 margin에서상방 1 mm부터 25 μm의공간을부여하였다. 완성된 wax pattern에 plastic sprue former를부착하고매몰을하였고소환과정을거친후, Ni-Cr 합금 (Wiron 99, BEGO Dental, Bremen, Germany) 을안정적으로용융시키기위하여고주파주조기 (Fornax T; Bego Dental) 로주조를하였다. 매몰, 소환, 주조는제조회사사용설명서를준수하였다. 2. 연구방법 1) 변연및내면적합도의정의 Reich 등 14) 과 Colpani 등 15) 의연구에서사용된정의를참고하여본연구에알맞게수정하여사용하였다. 이정의에의하면변연부의적합도 (margin are) 는 MA 부분, 경사도의적합도 (rounded chamfer) 를 RC 부분, 축벽의적합도 (axial 406
김기백외 : 도재소성과정이금속도재관의적합도에미치는영향 wall) 는 AW 부분, 절단연적합도 (incisal) 를 In 1, In 2 로정의하였다 (Fig. 2). 2) 실리콘복제본제작및측정변연및내면적합도는 silicone replica technique을이용하여측정하였다. 제작이완료된금속도재관용 coping의내면에 light body silicone (Aquasil Ultra XLV; Dentstly Caulk, Milford, MA, USA) 을채운후, 곧바로 stone die에위치시키고지압 (finger pressure) 을가하여적합시켰다. 일률적인지압이유지되기위하여전자저울상에서 50 N의압력이되도록가압하였다. 경화된 light body silicone을보철물로부터조심스럽게분리시킨다. 이 light body silicone film은 coping과 die와의간격을나타내주는역할을한다. Stone die에밀착된 light body silicone film은두께가매우얇아서찢어짐에대한저항이작고, 형태를유지하기힘들기때문에그위에강도가있는 heavy body silicone (Aquasil Ultra Monophase; Dentstly Caulk) 을추가적으로덮어안정화시켰다. 복제가완료된 silicone은 razor blade를사용하여순-설, 근-원심방향으로분할하였고, 그실리콘의두께를 160배율의 digital microscope (KH-7700; Hirox, Tokyo, Japan) 로관찰하였다 (Fig. 3). 3) Ni-Cr alloy 금속도재관제작 (Ni-Cr Metal Ceramic, NMC 그룹 ) 1차측정이끝난후 NCC 그룹에동일한치과기공사가제조회사의권장사항을준수하여금속도재관을완성하였다. 사용된도재는 Noritake Super Porcelain EX-3 (Noritake Dental Supply Co., Kyoto, Japan) 이며도재소성과정은 Table 1과같다. 완성된금속도재관은 1차측정때와마찬가지로 5부분측정하였으며, 측정방법도실리콘복제기술을이용하였다. 측정된실리콘의단면은디지털전자현미경을이용하여 160배확대하여측정하였다. 4) 통계분석통계분석은 SPSS ver. 12.0 for Windows 프로그램 (SPSS Inc., Chicago, IL, USA) 을이용하였다. 상부도재축성과정전과후인 NCC 그룹과 NMC 그룹의변연적합도및내면적합도의변화를평가하기위하여, 정규성검정을실시한후모수검정인대응표본 t검정 (paired t-test) 으로분석하였으며, 제 1종오류의수준은 0.05로하였다. 결과 NCC 그룹과 NMC 그룹의변연및내면적합도를측정한 Fig. 2. Definition of marginal and internal fit. MA: margin area, RC: rounded chamfer, AW: axial wall, In: incisal. Fig. 3. Measurement of marginal and internal fit by digital microscope at 160 magnification. Table 1. Firing Schedules for Veneering Porcelains Procedure Start temperature ( o C) Drying time (min) Temperature increase ( o C/min) Final temperature ( o C) Holding time (min) Degassing 300 0 30 1,080 20 Opaque 500 8 65 980 1 Body 600 7 45 920 0 407
J Dent Hyg Sci Vol. 14, No. 3, 2014 Table 2. Light Body Silicone Thickness (μm) for 5 Reference Points in Ni-Cr Alloy Core (NCC) Group and Metal-Ceramic Crown (NMC) Group Reference point NCC group NMC group p-value MA 50.6±11.8 59.5±11.3 0.102 RC 56.5±12.5 62.1±11.2 0.216 AW 46.4±13.0 61.9±15.5 0.062 In 1 77.4±10.4 82.8±9.00 0.179 In 2 71.5±13.5 75.2±9.40 0.316 Values are presented as mean±standard deviation. MA: margin area, RC: rounded chamfer, AW: axial wall, In: incisal. 결과 MA 부위에서의평균 ± 표준편차는 Table 2와같이 NCC 그룹 50.6±11.8 μm, NMC 그룹 59.5±11.3 μm였고, RC 부위에서는 NCC 그룹 56.5±12.5 μm, NMC 그룹 62.1±11.2 μm, AW 부위는 NCC 그룹 46.4±13.0 μm, NMC 그룹 61.9±15.5 μm였다. 절단연부위의 In 1 부위는 NCC 그룹 77.4±10.4 μm, NMC 그룹 82.8±9.0 μm, In 2 에서는 NCC 그룹 71.5±13.5 μm, NMC 그룹 75.2±9.4 μm였다. 두그룹에서각각측정된 5부위의평균을대응표본 t검정을실시하여평균을비교한결과에서는모든부위에서유의한차이를보이지않았다 (p>0.05). 각측정된 5부위를구분없이전체의평균 ± 표준편차를측정한결과 Fig. 4에서와같이 NCC 그룹에서는 67.1±23.3 μm, NMC 그룹은 74.4±21.9 μm로나타났으며, 두그룹간의평균비교를위하여실시한대응표본 t검정의결과 p=0.044로통계적으로유의한차이를보였다 (p<0.05). 고찰 본연구에서는상부도재축성과정시금속도재관의변연및내면적합도에미치는영향을확인하기위하여두차례로나누어측정한후그결과값을비교하였는데, 1차는 lost wax technique을이용하여 NCC (Ni-Cr) 를제작한후도재를축성하기전에실시되었고, 2차측정은 1차측정이끝난후 NCC (Ni-Cr) 위에치과용도재를축성한후금속도재관을완성한뒤에측정하였다. 측정방법은총 5부위로나누어측정하였고, 순-설, 근-원심 4방향으로분할하여실리콘복제기술을사용하였다. 그결과 Table 2과같이측정된 5부위모두에서통계적으로유의한차이를보이진않았지만 (p>0.05), NCC (Ni-Cr) 의변연및내면적합도보다상부도재를축성하고소성하는과정을거친금속도재관의변연및내면적합도가측정된 5부위에서모두비교적큰측정값을 Fig. 4. Total mean±standard deviation (SD) for all reference points (n=200) of NMC group according to porcelain firing process (p<0.05). NCC group: Ni-Cr alloy core group, NMC group: metal-ceramic crown group. 보였다. 선행연구를보면금속도재관이상부도재소성과정에의해영향을받는다고하였고 7,16), Balkaya 등 17) 은금속도재관제작시뒤틀림변형은사용된합금의종류, 도재가소성되는동안발생되는수축량의차이, 하부코어의디자인, 두재료간의열팽창계수의차이그리고변연부디자인등에영향을받는다고보고하였다. Buchanan 등 7) 은금속과도재의수축계수가다르므로하부금속코어에도재를축성하고소성하는과정에서금속도재관의변형이생긴다고보고하였으며, 도재는강성의물질인반면하부금속은탄성물질이기때문에소성후완성된금속도재관보철물과지대치와의변연간격이증가된다고하였다. 본연구에서도하부코어상태일때보다금속도재관상태일때지대치와의간격이증가된것을확인하였으며, 원인은위와같은원인으로생각된다. 금속도재관제작시금속코어위에도재를각단계별로여러번소성하게된다. 그중에서금속코어의산화막처리를위한소성단계와금속도재관완성후광택을부여하기위하여글레이즈처리를소성단계에서가장많은변형이발생된다고보고하였으며 16), 그이유로는산화막처리와글레이즈처리단계가가장고온으로소성하기때문이라고보고하였다. 같은이유로 Campbell과 Pelletier 18) 는금속도재관의뒤틀림변형의대부분은금속도재관의산화막소성과정에서발생한다고보고하였다. 이와같은결과들을토대로금속도재관제작시 Ni-Cr 합금으로제작된코어위에상부도재를축성하고소성하는과정이금속도재관의변연및내면적합도에영향을미친다고볼수있다. 이러한실험방법으로측정된결과치가임상적으로허용가능한범위에속하는지에대한기준에대해판단해보아야 408
김기백외 : 도재소성과정이금속도재관의적합도에미치는영향 할것이다. 임상적으로허용가능한변연간극의범위에대한여러연구가보고되고있다. 보철물의변연적합도는 American Dental Association specification 19) 에서 접착된보철물의임상적허용한계 를 25 μm 이하로간주하였으나, 실제로이런적합도를얻는것은쉽지않다. Sorensen 등 20) 은변연오차로인해발생하는골소실등을억제하기위해서는변연간극이 50 μm 이하이어야한다고하였고, Assif 등 21) 의연구에따르면평균적인변연적합도가약 140 μm 라고하였고, Hung 등 22) 의연구에서는 50 75 μm로제시하였다. 이와같이변연적합도에관한임상적허용한계를결정하는것은연구자에따라많은차이를나타냈다. 이렇듯임상적기준에대하여여러가지견해가있었지만, 아직까지많은선행연구들에서는 McLean과 von Fraunhofer의연구 23) 에서제시하였던 120 μm의변연간격을임상적허용한계로기준을두고있다. 본연구에서나타난모든그룹에서의변연적합도는근-원심, 순-설방향모두에서 100 μm 미만의간격을보였다. 이에따라 120 μm를임상적허용기준으로보았을때모든실험그룹의변연간격은임상적으로허용가능한한계내에존재하였다. 하지만본연구에서는변연부의디자인을 chamfer 형태로만삭제한것과, 시편수가 10개이긴하였으나단일금속도재관보철물한가지증례의시편만을가지고실험하였다는한계점이있었다. 때문에추후에수행될연구에서는보다길이가긴교의치를포함한다양한증례의시편과다양한변연부의디자인그리고코어의디자인도다양하게시편을제작하여각각의변수에따른소성과정이적합도에영향을미치는가에대한연구가추가적으로수행될필요가있다. 요약 본연구는심미보철치료에서사용되는금속도재관제작시 Ni-Cr alloy 하부구조물에상부도재를축성하고소성하는과정이완성된보철물의적합도에미치는영향을조사함으로써임상적허용을재확인하기위함이다. 1차로 lost wax technique으로제작된 NCC (Ni-Cr alloy core) 의변연및내면적합도를측정하였고, 2차로 NCC에상부도재축성, 소성하여금속도재관을최종완성하여 2차로측정한뒤비교한결과는다음과같다. 금속도재관제작시 Ni-Cr alloy로제작된코어위에상부도재를축성하고소성하는과정이금속도재관의적합도를악화시키는결과를보였으며, 부위별구분없이두그룹에서측정된모든값의평균을비교한결과 NCC 그룹에서는 67.1±23.3 μm, NMC 그룹에서는 74.4±21.9 μm로나타났으며통계적으로유의한차이를보였다 (p<0.05). 이와같은결과를토대로 Ni-Cr alloy로금속도재관제작시상부도재를축성하는과정에서적합도를악화시킨다는결론을얻었으나, 본실험에서측정된결과값은임상적허용수치 (120 μm) 를넘지않아적합도의기준으로평가하였을때임상적으로허용가능할것으로생각된다. References 1. Azer SS, Ayash GM, Johnston WM, Khalil MF, Rosenstiel SF: Effect of esthetic core shades on the final color of IPS Empress all-ceramic crowns. J Prosthet Dent 96: 397-401, 2006. 2. Brecker SC: Porcelain bakes to gold-a new medium in prosthodontics. J Prosthet Dent 6: 801-810, 1956. 3. Rosenstiel SF, Land MF, Fujimoto J: Contemporary fixed prosthodontics. 4th ed. Mosby, St. Louis, pp.599-608, 2006. 4. Wataha JC: Alloys for prosthodontic restorations. J Prosthet Dent 87: 351-363, 2002. 5. Eliasson A, Arnelund CF, Johansson A: A clinical evaluation of cobalt-chromium metal-ceramic fixed partial dentures and crowns: A three- to seven-year retrospective study. J Prosthet Dent 98: 6-16, 2007. 6. Shillingburg HT Jr, Hobo S, Fisher DW: Preparation design and margin disortion in porcelain-fused-to-metal restorations. J Prosthet Dent 29: 276-284, 1973. 7. Buchanan WT, Svare CW, Turner KA: The effect of repeated firings and strength on marginal distortion in two ceramometal systems. J Prosthet Dent 45: 502-506, 1981. 8. Dederich DN, Svare CW, Peterson LC, Turner KA: The effect of repeated firings on the margins of nonprecious ceramometals. J Prosthet Dent 51: 628-630, 1984. 9. Anusavice KJ, Carroll JE: Effect of incompatibility stress on the fit of metal-ceramic crowns. J Dent Res 66: 1341-1345, 1987. 10. Shokry TE, Attia M, Mosleh I, Elhosary M, Hamza T, Shen C: Effect of metal selection and porcelain firing on the marginal accuracy of titanium-based metal ceramic restorations. J Prosthet Dent 103: 45-52, 2010. 11. Pierce LH, Goodkind RJ: A status report of possible risks of base metal alloys and their components. J Prosthet Dent 62: 234-238, 1989. 409
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