대한치과보철학회지 :Vol. 45, No. 5, 2007 임플랜트지지상부구조물에서나사조임순서와조임방법이풀림토크값에미치는영향 서울대학교치과대학치과보철학교실 1,2,3,4, 삼성서울병원치과진료부보철과 1, 성균관대학교의과대학치과학교실 5 최정한 1 김창회 2 임영준 3 김

대한치과보철학회지 :Vol. 45, No. 5, 2007 임플랜트지지상부구조물에서나사조임순서와조임방법이풀림토크값에미치는영향 서울대학교치과대학치과보철학교실 1,2,3,4, 삼성서울병원치과진료부보철과 1, 성균관대학교의과대학치과학교실 5 최정한 1 김창회 2 임영준 3 김명주 4 이석형 5 Ⅰ. 서론치과용임플랜트는 Bra nemark 1 에의해골유착개념이도입된이래로완전및부분무치악환자에있어높은성공률을보여왔다. 2-5 그러나이러한높은성공률에도불구하고임플랜트치료시, 생물학적인문제 (biologic complication) 뿐만아니라, 나사의풀림과파절, 지대주의파절, 도재의파절, 금속구조 (framework) 의파절, 그리고임플랜트의파절등의기술적인문제 (technical complication) 도빈번히발생하였다. 3,6-18 이중에서나사의풀림은기능력하에서바람직하지못한응력분산과과부하를야기하여, 이차적으로다양한생물학적그리고기술적문제들을야기할수있으므로예방과초기진단이임상적으로매우중요하다. 나사풀림의원인으로는부적절한전하중 (preload), 부적절한임플랜트의위치, 부적절한교합양식 (occlusal scheme) 또는금관의해부학적형태, 부적절한나사형태, 과도한교합력, 그리고상부구조물의불량한적합등이있다. 19-21 임플랜트보철물에서나사조임의목적은나사풀림을방지하도록적절한전하중을사용하여나사연결부 (screw joint) 의안정성을얻는것이다. 22 적절한전하중은나사의형태 (geometry), 서로조여지는나사와임플랜트부품 (component) 간의접촉관계, 마찰 력, 그리고재료의성질에영향을받는다. 22-25 불량한적합을갖는상부구조물을나사로연결하는것은상부구조물, 임플랜트 / 지대주복합체, 그리고지지조직에높은전하중응력 (preload stress) 을야기하며, 기능력이가해질때시간의흐름에따라임플랜트나보철구성요소 (component) 들의풀림이나파절을야기할수있다. 26-30 따라서나사풀림을예방하거나줄이기위해선정확한적합을갖는상부구조물을제작및평가하는것이필요하다. 정확한적합을갖는상부구조물은상부구조물과임플랜트부품 (component), 그리고임플랜트에인접한골에발생되는응력을감소시키는데중요하다. 6,31,32 그러나상부구조물의정확한적합도 (precise fit) 는현재사용되고있는인상법과기공작업에의한최종모형 (definitive cast) 으로부터얻기가거의불가능하며, 소위, 수동적적합 (passive fit) 이라고표현되는임플랜트치료의성공을위해요구되는상부구조물의적합도는아직구체적인값으로정의된바없고, 실제임상에서는술자에의해여러가지임상적평가법을통해주관적으로판단되어지고있다. 33,34 따라서임플랜트상부구조물을지대주나임플랜트에나사로연결하게되면부정확한적합도로인해항상상부구조물, 임플랜트 / 지대주복합체, 그리고지지조직에응력이발생하게된다. 33,34 나사풀림현상을측정하는방법으로는, 나사길이의 이연구는서울대학교신임교수연구정착금으로지원되는연구비에의하여수행되었음. 653

변형측정 26, strain gauge를이용한전하중의측정 35, 및풀림토크값 (detorque value) 의측정 36 등이있다. 이중나사의풀림토크값은연결부의안정성을평가하는지표의하나로, 나사풀림직전에나사에남아있는전하중의척도로서임플랜트보철물의적합도에의해영향을받는다. 임플랜트지지상부구조물을지대주나임플랜트에나사로연결할때발생되는응력과나사풀림을최소화하기위해 Hobo 등 37 은원형순서 (circular order) 보다는바퀴를조이는순서 (cross-wise order) 로나사를조일것을추천하였으며, Jemt 38 는중앙에위치한나사부터시작하여최종적으로가장바깥쪽의나사를조이는방법을추천하였다. 그리고나사조임순서에따른발생응력에관한여러연구에서, 상부구조물이비교적정확한적합을갖는경우에는서로다른나사조임순서에대해발생되는응력에차이가없으나불량한적합을갖는경우에는차이를보인다고보고되었다. 30,39,40 지금까지임플랜트지지상부구조물에서나사조임순서에따른상부구조물 30, 지대주 40 또는모형표면 39 등에서의발생응력을비교한연구는있었으나, 나사조임순서및나사조임방법에따른나사의풀림토크값을비교한연구는미미한실정이다. 본연구는상부구조물이비교적정확한적합을갖는상황을재현하기위해서, 임플랜트에직접연결되는상부구조물을먼저제작한후, 이것을픽업인상채득하여만든모형상에서세가지나사조임순서와두가지나사조임방법에따른풀림토크값을비교하여나사조임순서와나사조임방법이나사풀림현상에미치는영향을알아보고자하였다. Ⅱ. 연구재료및방법 1. 상부구조물제작 Replica ST 22509; Astra Tech AB, Mölndal, Sweden) 가서로평행하게아크릴릭레진 (Pattern Resin; GC Corporation, Tokyo, Japan) 으로고정하였다. 각고정체유사체에지대주 (Cast-to Abutment ST 22829; Astra Tech AB) 를, 육각을제거한후, 연결하고단면이직사각형 (6 4 mm) 인납형을제작한후, 제4형금합금 (Jel-4; Jelenko, Armonk, New York, USA) 으로주조하여네개의임플랜트에직접연결되는상부구조물을제작하였다. 2. 실험모형의제작상부구조물과비교적정확한적합을갖는모형을제작하기위해하악모형에상부구조물을유도핀 (Guide Pin; Astra Tech AB) 으로연결한후 (Fig. 1), 저점성의실리콘인상재 (Extrude Wash; Kerr Co., CA, USA) 와아크릴릭레진 (SR Ivolen; Ivoclar Vivadent, Schaan, Liechtenstein) 으로제작한맞춤트레이를이용하여픽업인상을채득하였다. 맞춤트레이는인상채득 24시간전에제작되어실온에서보관되었으며 41,42, 인상채득 15분전에적절한접착제 (adhesive) 가도포되었다. 43 실온에서인상체의완전한중합을위해정상중합시간의두배인 8분후인상체를모형으로부터분리하였다. 44 그후인상체내의상부구조물에네개의임플랜트고정체유사체를토크렌치 (Torque Wrench 24075; Astra Tech AB) 를이용하여 10 Ncm 의힘으로조심스럽게연결하고제4형치과용초경석고 (GC FUJIROCK EP; GC Europe, Leuven, Belgium) 를제조사의지시에따라진공혼합하여붓고완전한경화를위해 1시간후분리하였다 (Fig. 2). 이과정을 6회반복하여총여섯개의실험모형을제작하였으며, 최소 24시간이상실온에서보관후나사의풀림토크값을측정하였다. 완전무치악하악모형을아크릴릭레진 (Orthodontic Resin Clear; Dentsply International Inc., Milford, DE, USA) 으로제작하고이공간부위 (interforaminal area) 에중심간거리가약 15 mm 되도록네개의구멍을형성한후밀링머신을이용하여네개의임플랜트고정체유사체 (Fixture 3. 풀림토크값의측정내부연결임플랜트보철물에서나사조임순서와나사조임방법이나사풀림현상에미치는영향을알아보기위해상부구조물을각실험모형에위치시킨후, 세가지나사조임순서와두가지나사조임방법 654

Fig. 1. An implant superstructure that connected directly to four implants (Astra Tech) of a fully edentulous mandibular acrylic resin model by guide pins before pickup impression. Fig. 2. A dental stone working cast made from a pickup impression of the superstructure. Fig. 3. Electric torque motor (ElcoMed SA-200C; W&H Dentalwerk, Buermoos, Austria). Fig. 4. Measurement of detorque values: Working casts were placed in the rigid holding device and the screw driver was carefully oriented in the long axis of the implant during screw tightening and detorque. 으로타이타늄나사 (Abutment Screw 22568; Astra Tech AB) 를조인후, 각나사의풀림토크값을측정하였다. 이때측정시실험모형의회전을방지하기위해모든실험모형은견고한장치에고정되었으며, 가장왼쪽에조여지는나사를 1번나사로하고가장오른쪽의나사를 4번나사로명명하였다. 먼저, 나사조임순서의영향을알아보기위해 1-2- 3-4, 2-4-3-1, 그리고 2-3-1-4의순서로 10 Ncm의힘으로조이고, 다시같은순서로최종조임토크값인 20 Ncm까지조인후 (2-step 방법 ) 각나사의풀 림토크값을측정하였다. 또한나사조임방법의영향을알아보기위해 2-3-1-4의순서로한번에최종조임토크값인 20 Ncm까지조인후 (1-step 방법 ) 각나사의풀림토크값을측정하여같은순서 (2-3-1-4) 의 2-step 방법과비교하였다. 각나사는전기토크모터 (ElcoMed SA-200C; W&H Dentalwerk, Buermoos, Austria)(Fig. 3) 를이용하여정해진토크로조였으며, 나사의풀림토크값은나머지세개의나사가조여져있는상태에서동일한장비를사용하여 0.1 Ncm 단위로측정하였 655

다. 전기토크모터는보정후사용하였으며, 나사의조임과풀림토크값의측정시드라이버가임플랜트의장축과평행이되도록주의하였다 (Fig. 4). 나사의마모를보상할수있는순서로측정하였으며, 측정시의오차를보상하기위해여섯개의실험모형에대해한번측정한후, 다시한번측정하여풀림토크값을총 2회측정하였다. 나사조임과풀림토크값의측정은한명의잘훈련된검사자에의해시행되었다. 4. 통계분석세가지나사조임순서에따른나사의풀림토크값과이때조여진순서별각나사의풀림토크값은 multi-way analysis of variance를이용하여유의수준.05 에서비교분석하였다. 또한두가지나사조임방법에따른나사풀림토크값도 multi-way analysis of variance를이용하여유의수준.05에서비교분석하였다. 그리고상부구조물에서어느한나사라도풀릴위험성을평가하기위해, 각나사조임순서와각나사조임방법에대한네개나사의풀림토크값중가장작은최소풀림토크값만을가지고 two-way analysis of variance를이용하여유의수준.05에서나사조임순서간과나사조임방법간의차이를비교분석하였다. Ⅲ. 결과 Table I 은나사를동일한나사조임방법 (2-step) 으로조였을때의각나사조임순서 (1-2-3-4, 2-4-3-1, 그리고 2-3-1-4) 와, 같은나사조임순서 (2-3-1-4) 로조였을때의각나사조임방법 (2-step 과 1-step) 에대한, 네개나사의풀림토크값의평균과표준편차를보여준다. 그리고세가지나사조임순서에대해네나사의조여진순서별풀림토크값의평균과표준편차는 Table II 와같다. 세가지나사조임순서에대한풀림토크값의평균은각각 12.3 Ncm, 12.6 Ncm, 그리고 12.0 Ncm였으며, multi-way analysis of variance는나사조임순서간에통계학적으로유의할만한차이점이없음을보여주었다 (p=0.2667)(table III). 그리고나사조임순서와무관하게조여진순서별네나사의풀림토크값의평균은처음에조여진나사부터 12.4 Ncm, 12.3 Ncm, 12.7 Ncm, 그리고 11.8 Ncm로가장마지막에조여진나사의풀림토크값이가장적었으나 (Table II), multi-way analysis of variance는조여진순서별나사의풀림토크값간에통계학적으로유의할만한차이가없음을보여주었다 (p=0.1331)(table III). 두가지나사조임방법에대한풀림토크값의평균은각각 12.0 Ncm와 12.2 Ncm로, multi-way analysis of variance는나사조임방법간에도통계학적으로유의할만한차이점이없음을보여주었다 (p=0.6302)(table IV). Table V 는각나사조임순서와각나사조임방법에서의네개나사의풀림토크값중최소값의평균과표준편차를보여준다. 세가지나사조임순서에따른최소풀림토크값의평균은각각 10.6 Ncm, 11.1 Ncm, 그리고 10.5 Ncm였으며, two-way analysis of variance는나사조임순서간에통계학적으로유의할만한차이점이없음을보여주었다 (p=0.3277) Table I. Detorque values (Ncm) for screw tightening sequence & method N Screw 1 Screw 2 Screw 3 Screw 4 N = 48 Mean SD Mean SD Mean SD Mean SD Mean SD Sequence 1-2-3-4 12 12.9 2.15 12.6 2.56 12.4 1.46 11.4 1.24 12.3 1.95 2-4-3-1 12 11.9 1.32 12.6 1.64 13.0 2.08 12.8 1.65 12.6 1.69 2-3-1-4 12 12.6 2.05 11.8 1.54 11.5 1.18 12.0 2.07 12.0 1.74 Method 2-step 12 12.6 2.05 11.8 1.54 11.5 1.18 12.0 2.07 12.0 1.74 1-step 12 13.1 2.42 10.8 2.47 12.5 2.12 12.4 2.13 12.2 2.37 656

Table II. Detorque values (Ncm) for screw tightening sequence as a function of screw order Sequence N 1 st Screw 2 nd Screw 3 rd Screw 4 th Screw Mean SD Mean SD Mean SD Mean SD 1-2-3-4 12 12.9 2.15 12.6 2.56 12.4 1.46 11.4 1.24 2-4-3-1 12 12.6 1.64 12.8 1.65 13.0 2.08 11.9 1.32 2-3-1-4 12 11.8 1.54 11.5 1.18 12.6 2.05 12.0 2.07 Total 36 12.4 1.80 12.3 1.92 12.7 1.85 11.8 1.57 Table III. Multi-way analysis of variance for screw tightening sequence Source DF Type III SS Mean Square F Value p-value* Reading 1 6.50 6.50 2.04 0.1553 Screw 3 5.34 1.78 0.56 0.6430 Sequence 2 8.50 4.25 1.33 0.2667 Order 3 18.12 6.04 1.90 0.1331 * A p-value <.05 level was considered significant. Table IV. Multi-way analysis of variance for screw tightening method Source DF Type III SS Mean Square F Value p-value* Reading 1 7.94 7.94 1.93 0.1683 Screw 3 28.03 9.34 2.27 0.0857 Method 1 0.96 0.96 0.23 0.6302 * A p-value <.05 level was considered significant. Table V. Minimum detorque values (Ncm) for screw tightening sequence & method N Minimum detorque value Mean SD Sequence 1-2-3-4 12 10.6 1.11 2-4-3-1 12 11.1 1.26 2-3-1-4 12 10.5 0.77 Method 2-step 12 10.5 0.77 1-step 12 9.8 1.40 (Table VI). 그리고두가지나사조임방법에따른최소풀림토크값의평균은각각 10.5 Ncm와 9.8 Ncm 로, two-way analysis of variance는나사조임방법간에도통계학적으로유의할만한차이점이없음을 보여주었다 (p=0.1643)(table VII). 나사의조임토크값에대한초기풀림토크값의비는각나사조임순서와나사조임방법에따라 60-63% 까지의값을보였다 (Table I). 657

Table VI. Two-way analysis of variance for screw tightening sequence as a function of minimum detorque value Source DF Type III SS Mean Square F Value p-value* Reading 1 < 0.01 < 0.01 < 0.01 0.9634 Sequence 2 2.71` 1.35 1.16 0.3277 * A p-value <.05 level was considered significant. Table VII. Two-way analysis of variance for screw tightening method as a function of minimum detorque value Source DF Type III SS Mean Square F Value p-value* Reading 1 0.30 0.30 0.23 0.6360 Method 1 2.73 2.73 2.08 0.1643 * A p-value <.05 level was considered significant. Ⅳ. 고찰임플랜트지지상부구조물에서나사조임순서는나사풀림현상에영향을미칠수있을것이라는가정하에 Hobo 등 37 은원형순서 (circular order) 보다는바퀴를조이는순서 (cross-wise order) 로나사를조일것을추천하였으며, Jemt 38 는중앙에위치한나사부터시작하여최종적으로가장바깥쪽의나사를조이는방법을추천하였다. 나사조임순서에관한이전연구에서, 상부구조물이비교적정확한적합을갖는경우에는서로다른나사조임순서에대해발생되는응력에차이가없으나, 불량한적합을갖는경우에는차이를보인다고보고되었다. 30,39,40 Nissan 등 30 은다섯개의임플랜트가심어진주모형으로부터연결인상법을이용하여제작한 30개의모형에, 주모형과수동적적합을갖는상부구조물을두가지나사조임순서로조인후, 상부구조물에발생되는응력을측정비교한결과두가지나사조임순서간에통계학적으로유의성있는차이가없었다고보고하였다. 또한 Duyck 등 40 은여섯개의임플랜트가심어진네개의모형에각각임상적수동적합 (clinically passive fit) 을갖는상부구 조물을만든후, 다섯가지나사조임순서로조인후, 지대주에발생하는응력을측정비교한결과, 나사조임순서간에통계학적차이가없었다고보고하였다. 그러나이두연구는 Hobo 등 37 과 Jemt 38 가추천한나사조임순서에대해서는평가하지않았다. Watanabe 등 39 은세개의임플랜트가심어진주모형에서, 수동적합법 (passive-fit method) 과납착법 (soldering method) 을이용하여각각네개의상부구조물을제작한후, 세가지나사조임순서로조인후, 주모형에발생되는응력을측정비교한결과, 수동적합법으로제작된상부구조물을연결한경우엔발생응력이상대적으로작고나사조임순서에따른통계학적차이를보이지않았으나, 납착법으로제작된상부구조물을연결한경우에는상대적으로큰응력이발생하였으며, 나사조임순서에따라발생응력에차이가있고, 가운데부터조인경우에응력값이가장적었다고보고하였다. 본실험은상부구조물이비교적정확한적합을갖는경우에나사조임순서가나사풀림현상에미치는영향을평가하기위해, 네개의내부연결임플랜트에직접연결되는상부구조물을제작하고, 이를픽업인상채득하여여섯개의실험모형을제작한후, Nissan 등 30 의실험에서비교한원형순서 (1-2-3-4) 와 658

Hobo 등 37 이제시한순서 (2-4-3-1), 그리고 Jemt 38 가제시한순서 (2-3-1-4) 에대해나사의풀림토크값을측정비교하였다. 또한나사조임방법이나사풀림현상에미치는영향을평가하기위해, 한가지나사조임순서 (2-3-1-4) 를사용하여, 일정한토크값으로초기연결을한후, 다시같은순서로최종조임토크값으로나사를조이는방법 (2-step 방법 ) 과처음부터최종나사조임토크값으로조이는방법 (1-step 방법 ) 에대한나사의풀림토크값을측정비교하였다. 실험결과풀림토크값은세가지나사조임순서간에통계학적으로유의성있는차이를보이지않았으며 (p=0.2667)(table III), 이것은상부구조물이비교적정확한적합을갖는경우라면, 나사조임순서는발생응력뿐만아니라나사의풀림토크값에도영향을미치지않으며, 결과적으로나사풀림현상에영향을미치지않는다는것을의미한다. 또한전체나사조임순서와무관하게몇번째조여진나사인지에따른풀림토크값을비교해본결과, 처음에조여진나사에서부터마지막에조여진나사간에차이가없었으며 (p=0.1331)(table III), 두가지나사조임방법간에도차이를보이지않았다 (p=0.6302)(table IV). 임플랜트지지상부구조물에서나사풀림현상은가장취약한나사에서부터시작되며, 이경우기능력 (functional load) 이나머지나사에집중되어결국다른나사들의풀림또는파절을야기하게된다는점에서최소풀림토크값이전체나사의풀림토크값보다임상적으로더의미있다고할수있다. 본실험에서는나사조임순서간 (p=0.3277) (Table VI) 에, 그리고나사조임방법간 (p=0.1643) (Table VII) 에모두, 최소풀림토크값에도차이가없었다. 따라서비교적정확한적합도를갖는상부구조물은나사조임순서나나사조임방법에따라나사풀림현상에차이가없다고할수있다. 나사를조인직후의나사의풀림토크값은항상조임토크값보다작은데 26,45,46, 이것은나사를조일때조임력의일부가마찰력으로소모되기때문이다. Schulte 등 47 은나사의조임토크값과전하중의상관관계에영향을주는요소로, 연결되는면간의적합도, 나사의길이및폭, 임플랜트구성품의크기, 그리고재료가있다고하였다. 나사의조임토크값에대한초기의풀림토크값의비에대한몇몇연구들을 살펴보면, Jaarda 등 48 은일자형금나사 (slotted gold retaining screw) 를 10 Ncm로조였을경우그비가 82% 이었다고보고하였으며, Haack 등 26 은 UCLA 지대주를 20 Ncm 로조였을경우엔금이나타이타늄나사모두 75-80% 였고, 타이타늄나사를 30 Ncm 로조였을경우엔 81% 이었다고보고하였다. 그리고김등 49 은타이타늄지대주나사를 30 Ncm로조였을경우 91% 이었다고보고하였다. 그러나이들연구는모두단일치임플랜트를사용하였으며, 다수의임플랜트에의해지지되는보철물에대한연구는없었다. 네개의내부연결임플랜트에직접연결되는상부구조물을타이타늄나사를사용하여 20 Ncm 로조인본연구에서는나사의조임토크값에대한초기풀림토크값의비가 60-63% 로단일치임플랜트를이용한이전연구들에서보고된것보다작은값을보였다. 이것은단일치임플랜트의경우엔연결되는면간의적합도가제조오차 (manufacturing error) 를허용하는범위내에서제조사에의해상당히정확하게조절되나, 다수의임플랜트에의해지지되는보철물의경우엔여러가지기공및임상과정중에발생하는오차로인해연결되는면간의적합도가상대적으로떨어지기때문이다. 또한본실험에서사용한내부연결임플랜트는외부육각임플랜트에비해보다많은접촉면을가지므로, 감소된적합도에의해보다많은양의조임토크가마찰력으로소모되었을것이다. 본실험에서는비교적정확한적합도를재현하기위해상부구조물을픽업인상채득하여실험모형을만들었으나, 이러한적합도는실제임상에서는재현할수없으며, 임상에서얻을수있는적합도를갖는상부구조물에서나사조임순서와나사조임방법의영향에대해서는추가적인실험이필요하다. 본실험은전하중과관련있는나사의초기풀림토크값만을측정하였으나, 실제임상에서의나사풀림현상은하중이가해지는동안의부정확한적합도로인한상부구조물의진동과미세운동에의해발생되며, 임플랜트의결합방식에영향을받을수있다고알려져있다. 50,51 따라서, 다수임플랜트에의해지지되는보철물에있어서나사조임순서및나사조임방법이나사풀림현상에미치는영향을알아보기위해서는반복하중후의나사의풀림토크값에대한추가적인연구 659

가필요하리라생각된다. 그리고본연구의실험적자료는 conical seal design을특징으로하는내부연결임플랜트시스템에대한것으로다수임플랜트에의해지지되는보철물에서나사조임순서및나사조임방법이나사연결부의안정성에미치는영향을분석비교하는데기초적인자료로만해석되어야할것이며, 다른형태의연결양식을갖는여러가지임플랜트시스템에대해서는추가적인연구가필요할것으로생각된다. Ⅴ. 결론임플랜트에직접연결되는상부구조물을픽업인상채득하여만든모형상에서세가지나사조임순서와두가지나사조임방법에따른나사의풀림토크값을측정하여다음과같은결과를얻었다. 1. 나사조임순서에대한나사의풀림토크값은통계학적으로유의성있는차이를보이지않았다 (p=0.2667). 2. 조여진순서별각나사의풀림토크값간에통계학적으로유의성있는차이가없었다 (p=0.1331). 3. 나사조임순서에대한최소풀림토크값은통계학적으로유의성있는차이를보이지않았다 (p=3277). 4. 나사조임방법에대한나사의풀림토크값은통계학적으로유의성있는차이를보이지않았다 (p=0.6302). 5. 나사조임방법에대한최소풀림토크값은통계학적으로유의성있는차이를보이지않았다 (p=0.1643). 6. 나사의조임토크값에대한초기풀림토크값의비는각나사조임순서와나사조임방법에따라 60-63% 까지의값을보였다. 이러한연구결과는, 본실험과같은조건하에서정확한적합도를갖는내부연결임플랜트지지고정성국소의치는나사조임순서나나사조임방법에따라하중전나사연결부의안정성에차이가없다는것을의미한다. 참고문헌 1. Bra nemark PI. Osseointegration and its experimental background. J Prosthet Dent 1983;50:399-410. 2. Adell R, Lekholm U, Rockler B, Branemark PI. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;10:387-416. 3. Lekholm U, et al. Osseointegrated implants in the treatment of partially edentulous jaws: a prosopective 10-year multicenter study. International Journal of Oral & Maxillofacial Implants 1994;9:627-635. 4. Naert I, Koutsikakis G, Duyck J, Quirynen M, Jacobs R, van Steenberghe D. Biologic outcome of implant-supported restorations in the treatment of partial edentulism. Part I: a longitudinal clinical evaluation. Clin Oral Implants Res 2002;13:381-389. 5. Naert I, Koutsikakis G, Quirynen M, Duyck J, van Steenberghe D, Jacobs R. Biologic outcome of implant-supported restorations in the treatment of partial edentulism. Part 2: a longitudinal radiographic study. Clin Oral Implants Res 2002;13:390-395. 6. Kallus T, Bessing C. Loose gold screws frequently occur in full-arch fixed prostheses supported by osseointegrated implants after 5 years. Int J Oral Maxillofac Implants 1994;9:169-178. 7. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: the Toronto study. Part III: Problems and complications encountered. J Prosthet Dent 1990;64:185-194. 8. Wyatt CC, Zarb GA. Treatment outcomes of patients with implant-supported fixed partial prostheses. Int J Oral Maxillofac 660

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ABSTRACT THE EFFECT OF SCREW TIGHTENING SEQUENCE AND TIGHTENING METHOD ON THE DETORQUE VALUE IN IMPLANT-SUPPORTED SUPERSTRUCTURE Jung-Han Choi, D.D.S., M.S.D. 1, Chang-Whe Kim, D.D.S., M.S.D., Ph.D. 2, Young-Jun Lim, D.D.S., M.S.D., Ph.D. 3, Myung-Joo Kim, B.S., D.D.S., M.S., Ph.D. 4, Seok-Hyung Lee, D.D.S., D.M.D. 5 1,2,3,4 Department of Prosthodontics, College of Dentistry, Seoul National University 1 Department of Prosthodontics, The Institute of Oral Health Science, Samsung Medical Center 5 Department of Prosthodontics, Samsung Medical Center, Sungkyunkwan University School of Medicine Statement of problem: The screw detorque value is a measure of the preload remaining in the screw just before detorquing. Purpose: This study evaluated the effect of different screw tightening sequences and tightening methods on detorque values for a well-fitting implant superstructure. Material and method: An implant superstructure that connected directly to four implants (Astra Tech) was fabricated on a fully edentulous mandibular acrylic resin model. Six wellfitting dental stone casts were made with a pickup impression of the superstructure from the acrylic resin model. To evaluate the effect of three screw tightening sequences (1-2-3-4, 2-4-3-1, and 2-3-1-4) and two tightening methods (2-step and 1-step) on the stability of screw joint, the detorque values for a well-fitting implant superstructure were measured twice after screw tightening using 20 Ncm. Detorque values were analyzed using multi-way analysis of variance and two-way analysis of variance at a.05 level of significance. Results: 1. The mean detorque values for three screw tightening sequences were 12.3 Ncm, 12.6 Ncm, and 12.0 Ncm, respectively. 2. The mean detorque values for two screw tightening methods were 12.0 Ncm, and 12.2 Ncm, respectively. 3. The mean of mimimum detorque values for three screw tightening sequences and for two tightening methods were 10.6 Ncm, 11.1 Ncm, 10.5 Ncm, and 9.8 Ncm, respectively. 4. No statistically significant differences among the variables of screw tightening sequence and tightening method were found (p>.05) for detorque values and for mimimum detorque values. Conclusion: Within the limitations of this study, the screw tightening sequence and tightening method did not have a significant effect on the detorque values for a well-fitting implant superstructure. Key words : Screw tightening sequence, Screw tightening method, Detorque value, Pickup impression, Internal connection implant 664