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1 - 대한치과보철학회지 Vol. 30 No. 3, 하악유리단국소의치하에서 back-action 클래스프설계변화에따른광탄성응력분석 조선대학교치과대학치과보철학교실조선대학교치과대학치과재료학교실 * 임수령ㆍ계기성ㆍ고영무 * I. 서론 유리단국소의치의지지는주로잔존조직에서얻 고제한된양을지대치에서얻게되는데국소의치 의지지도직인지대치와잔존치조조직은생체일부 분으로서저작시교합력하에있으므로생역학적인 고려가요구되며, 치근막으로둘러싸인치아와탄 력있는점막조직에서지지를받으므로의치상에가 해지는외력에의하여지대치에응력이발생되고 치주조직의파괴를유발시킬수있다. 국소의치가 기능운동을할때지대치와잔존치조직에발생하는 응력양상은많은학자들의관심사였으며직접유 지장치의설계변화에따라지지조직에미치는영향 (3, 5-7, 9, 13, 14, 19, 에대해서다각적으로연구되어왔다 29-32, 37, 40, 44-46, 53, 64-66, 68). 따라서지대치와지지조직의부담을최소화할 수있는이상적인국소의치의설계를필요로하며 (3, 6, 29, 30, 42) 국소의치의주유지를얻는직접유지장치 의형태를변화시킴으로써지대치에미치는힘을 (3, 6, 36, 37, 감소시킬수있는가능성이제시된바있다 41, 47). Applegate (10) 및 Lee (48) 는의치상의연장, Cecconi 등 (18), Maxfield 등 (50) 및 Taylor 등 (64) 은의 치상의적합도, Bec-ker (12), Colman (21), Kaires (42) 및 Levin 등 (49) 은교합면의설계, Plotnick (57) 은대 합치의양상, Kratochvil 등 (45) 및 Eick 등 (27) 은국소 의치주조체의적합도에따른응력분석에관해연 구한바있다. 또한 Cecconi (17, 18), Clayton 등 (20) Kaires (40, 41), Shohet (60) 및 Thomp-son 등 (66) 의연 구에서는어떤클래스프설계가지대치운동을가 장최소로유발하는가에관하여보고하였다. 직접 유지장치의설계시고려할점은교합면레스트의 위치, 유지부의위치, clasp 의접근방향등매우다 양하며그만큼각구성성분에대한상반된견해들 이연구보고되고있다. 국소의치의응력분석에관 한방법은 Mühlemann (54, 55) 이 dial gauge 를이용 한이래기계적또는전기적 strain gauge 를응용 한방법 (28, 31, 33, 34, 39) 으로시작되어서, Kratochvil 379

2 등 (45), Thomp-son 등 (66) 및 White (68) 에의한광탄성응력분석법, Craig 등 (23), Takahashi 등 (62) 에의한유한요소법등으로이어져오고있다. 양측성유리단국소의치에서 back-action 클래스프의근원심연결방법의차이와교합면레스트위치변화에따라지대치및인접치의주위치조골과유리단잔존치조조직에발생하는응력의크기정도와분포양상을구체적으로비교한경우는드물어본연구는하악을생체와유사하게 3차원적인광탄성모형으로재현한후 2차원적인방법으로응력분포양상을관측검토하였다. Back-aciton 클래스프의경우유리단국소의치에서는일반적으로권장하지않는클래스프로간주되고있으나지대치가강한경우에는선별적으로사용될수있으며지대치가약한경우에는 splinting 하여어떻게 back-action 클래스프를설계해야가장유리한것인지 5가지유형의국소의치를각각광탄성모형에장착한후양쪽유리단중편측성수직집중하중을가하여의치상하부의잔존치조조직및지대치주위치조골에발생하는응력분포특성을광탄성응력분석법으로비교관찰한결과다소의지견을얻었기에이에보고하는바이다. 의대구치가결손된유리단국소의치 Kennedy 분류 I 급의실험모형을제작코저, 치아가없는사체의하악골체는알지네이트로인상을채득한후, 끓여서녹인파라핀왁스를주입하여하악골의형태를만들고타이포덴트상의치아를좌우제 1 및 2소구치와전치부위에배열하여양측성유리단파라핀왝스하악모형을제작하였다. 치아가배열된파라핀왝스하악모형을고무인상재를이용하여인상을채득하였다. 이때치아교합면은노출되도록하여 epoxy 레진주입시치아를고정할수있도록경석고로교합면을인기하였다. Epoxy resin(pl-1) 보다훨씬부드러운실리콘인상재를레진치아의치근면에 3-4회도포하여약 0.2mm 두께의치주인대를재현하였고, 끓는물로왝스가제거된인상체공간에미리제작된교합면인기경석고를이용, 치아를고정시킨후, PL-I epoxy 레진을혼합하여주입하였다. 광탄성실험모형을완성한후, 반사형광탄성응력측정법으로관찰하기위해은색분말페인트 (plastic cement- 1) 를광탄성하악실험모형의설측부에도포하였다 (Fig. 1). II. 실험재료및방법 1. 실험재료 1) 실험모형의제작 실험모형을제작하기위해서먼저하악좌우측 Fig. 1. Photoelastic cast coated with plastic cement

3 2) 실험국소의치의제작실험국소의치의제작을위하여광탄성하악모형의최후방지대치인제2소구치에 back action 클래스프가장착되도록설계하고교합면레스트씨트를근심면과원심면에각각형성했으며또한치조제점막을재현하기위하여약 2mm 두께의베이스플레이트왝스를한겹덮은후아가인상으로복제된매몰제모형상에서하악주연결장치는 6게이지의반이형의납형으로설측바금속주조물을각각주조제작하였고간접유지장치는 10 게이지납형으로좌우측제1소구치근심변연부에설계했으며, back-action 클래스프를차츰가늘어지는균일한두께로제작하였고, 의치상의유지부금속구조물은 12 게이지반원형, 왝스 strip 를사용하여열려진격자모양으로제작하였고, 최종지대치인좌우제2소구치에 mesial connection 과원심레스트를갖는 back-action 클래스프의경우, distal connection 과근심레스트를갖는 back-action 클래스프의경우, mesial connection 과근심레스트를갖는 back-action 클래스프의경우, distal connection 과근심및원심레스트를갖는 backaction 클래스프의경우, mesial connection 과근심및원심레스트를갖는 back-action 클래스프의경우인 5가지유형으로분리하였다 (Fig 2 : case 1-5). 그후무치악유리단부위에직접자가중합레진을이용하여레진의치상을부여한후치아배열을완성한실험국소의치를제작한후무치악부위에실리콘고무인상재로치조제점막을재현해주기위하여미리만들어둔약 2mm의레진의치상내면의빈공간에주입하여탄력성있는연조직점막을재현시켰다. Case 1 Case 2 Case 3 381

4 수있는응력이발생되도록우측제 1 대구치중심와 부위에 12.5kg 의편측수직집중하중을가한후, 응력분포상태를관측하였다. Case 4 Case 5 Fig. 2. Removable partial denture frameworks with five diff-erent types of the back-action clasp. Case 1. Mesial connection and distal rest Case 2. Distal connection and mesial rest Case 3. Mesial connection and mesial rest Case 4. Distal connection and the mesial and distal rest Case 5. Mwsial connection and the mesial and distal rest Fig. 3. Unilateral vertical loading on the distal extension remob-able partial denture. 2. 실험방법 1) 하중장치의설치 Fig. 3에보인바와같이하중장치의좌우평형을맞춘후실험모형을고정시켰고, 상호비교할 2) 반사형광탄성응력분석원래 3차원적모형의응력분석을할때는응력동결법을사용하여각모형의입체형상을절개해가면서응력분포를측정분석하는것이원칙이나, 이러한경우에는실험조건의수만큼광탄성하악골의모형을제작하여, 일정조건의하중과동결과정을거쳐야하는데, 실제실험을수행할때는각모형에동일조건을부여한다는것이거의불가능한 382

5 일이다. 따라서본연구에서처럼하나의광탄성하악골모형을만들어그모형에잘적합되는국소의치를여러개제작하면, 실험조건을일정하게유지할수있다는장점이있어상대비교가가능하므로실제광탄성모형의형태는 3차원이나, 입체모형의각 / 부위에발생되는응력을손쉽게관찰하기위하여 2차원적인반사형응력측정방법을선택하였다. 반사형원편광기를사용하기위하여 Fig. 4-1 와같이위치시켜, Model 232 null-balance compensator를이용하여검광자를검정색 (0차무늬차수 ) 이나타나도록조절하였다 (Fig. 4-2). III. 실험성적 유리단국소의치의치상의제1대구치에 12.5kg 의편측의수직집중하중을가한후 5종류의 back-action clasp가장착된광탄성하악골모형에무늬차수의크기와응력의분포상태를관찰해본결과 Fig. 5-Fig.15 에보인바와같은결과를얻었으며, 이때무늬차수의크기를계량하는데는 Table 1에보인 PL-1 재료의표준무늬차수로평가하였다. 1. mesial connection과원심레스트를갖는 back-action 클래스프 (Case 1) Fig 4-1. Reflective circular polar-iscope. (1) 하중측 Fig.6 는 Fig. 2, Case 1에보인형태의금속구조물로만들어진의치상으로 distal rest의직하방부터의치상하방부의후방부를따라서약 8mm폭으로 0.8차의무늬차수가균등히작용하고제2소구치의치근단부에 0.9차무늬차수가나타남을알수있다. 그리고레스트직하의기저면이접하는부위에도상부와유사한폭으로 0.6 차의무늬차수가나타나고있으며제2소구치와제1소구치의치근단끝에 0.2 차의응력집중부위가나타남을볼수있다. Fig Installing the null-balance compensator on the pola-riscope. (2) 비하중측비하중측의제2소구치, 제1소구치, 견치하단에도 차정도의응력집중부위가나타남을볼수있다. 이런결과는한쪽에만가한힘이금속구조물을따라전달되어반대편지대치에다소응력이나타남을볼수있다 (Fig. 7). 383

6 Table 1. Isochromatic fringe characteristics 2. distal connection과근심레스트를갖는 back-action 클래스프 (Case 2) (1) 하중측 Fig. 8은 Fig. 2, Case 2와같은금속구조물로만들어진의치상으로근심레스트의하부에는 Fig.1의경우와유사한 0.8 차의균등한무늬차수 가있으나, Fig.6의경우보다앞뒤로무늬차수의길이가약간더길며, 제2 소구치및제1 소구치치근단에도약간많은응력 ( 약 0.3차 ) 이발생되며제2 소구치의경우는레스트쪽의치근면을따라서약 0.6차정도의응력이발생하고있는데이는레스트쪽으로지대치가기울어지는경향을나타내주는결과이다. 384

7 (2) 비하중측이경우에는하중레스트쪽에서대부분의하중이지지되기때문에반대편지대치에는거의전달되는하중이없음을볼수있다 (Fig. 9). 3. mesial connection과근심레스트를갖는 back-action 클래스프 (Case 3) (1) 하중측 Fig. 10 는 Fig. 2, Case 3와같은금속구조물의의치상의광탄성사진으로, 의치상하부에전자와같은형태의의 0.8차의무늬차수가상하로위치하여분포하는데, 전자의경우보다무늬차수의길이가더짧으며제2소구치및제1 소구치의치근단에걸리는응력도 0.2차무늬차수정도의적은응력집중상태를보이고있다. 그런데이경우에는하중이가해지는쪽의기저부를따라전치부쪽으로반력의분포상태가 Fig. 6, 8의경우보다더길어서, 주로하중작용부하방에응력이분포된다고볼수있다. (2) 비하중측하중이가해지는반대편에는제2소구치치근단에약간의응력 (0.2 차의무늬차수 ) 이걸리는정도로응력의분산상태가가장양호한경우로판단되어진다 (Fig. 11). Fig. 2, Case 4와같은금속구조물의광탄성사진으로, Fig. 8 의경우와유사하게제2소구치의치근면을따라 0.6차정도의응력이발생되나 Fig. 8 의경우보다는치근면의무늬폭이더엷으며치근단직하방쪽에 0.3차정도의집중된응력상태를보이고있다. 또한제1소구치의치근단에도국부적으로 0.3 차의집중응력을볼수있다 (Fig. 12). (2) 비하중측이경우에는 Fig. 9 의경우와는달리비하중축의제2소구치및제 1소구치의치근단에미미하나마 0.2 차정도의집중응력이발생됨을볼수있다 (Fig. 13). 5. mesial connection과근심레스트및원심레스트를갖는 back-action 클래스프 (Case 5) (1) 하중측 Fig.2, Case 5와같은금속구조물의광탄성사진으로근심레스트의하부에 0.8차의무늬차수가분포되는양상은 Fig. 12의경우와유사하다. 제2 소구치에가해지는편중하중의영향은 case 4의경우보다적어서치근단쪽으로집중되는 0.6차의무늬차수를볼수있다 (Fig. 14). 4. distal connection과근심레스트및원심레스트를갖는 back-action 클래스프 (Case 4) (1) 하중측 (2) 비하중측이경우는 Case 4의경우와같이하중이작용하는반대편제2소구치와제1소구치치근단에미미하나마 0.2차정도의응력집중부가나타남을볼수있다 (Fig.15). 385

8 Fig. 5. No residual stress in the photoelastic mandible Fig. 6. Stress distribution under the mandibular distal extension removable partial denture with the mesial connection and the distal rest(loaded side) Fig. 7. Stress distribution under the mandibular distal extension removable partial denture with the mesial connection and the distal rest(unloaded side) Fig. 8. Stress distribution under the mandibular distal extension removable partial denture with the distal connection and mesial rest(loaded side) Fig. 9. Stress distribution under the mandi-bular distal extension removable partial denture with the distal connection and mesial rest(unloaded side) Fig. 10. Stress distribution under the mandibular distal extension removable partial denture with the mesial connection and mesial rest(loaded side) 386

9 Fig. 11. Stress distribution under the mandibular distal extension removable partial denture with the mesial connection and mesial rest(unloaded side) Fig. 12. Stress distribution under the mandibular distal extension removable partial denture with the distal connection and the mesial and distal rest(loaded side) Fig. 13. Stress distribution under the mandibular distal extension removable partial denture with the distal connection and the mesial and distal rest(unloaded side) Fig. 14. Stress distribution under the mandibular distal extension removable partial denture with the mesial connection and the mesial and distal rest(loaded side) IV. 총괄및고안 Fig. 15. Stress distribution under the mandibular distal extension removable partial denture with the mesial connection and the mesial and distal rest(unloaded side) 유리단국소의치에가해지는하중은지대치및 주위치조골, 의치상하방의잔존치조조직에전달 되게되는데, 치근막과치조점막의탄성차이로인 해유리단국소의치하에서발생하는응력의분포 는다양하며유리단국소의치설계의변화에따른 (9, 11, 13, 25, 31, 40, 41, 43, 47, 58, 응력의분석은매우어렵다 60). 그러나기능운동시유리단국소의치에나타나 387

10 는응력분포를분석하므로써, 지대치및치아주위조직등기타구강악계에위해작용없이기능을발휘할수있는이상적인국소의치의설계가고려되어야한다 (1, 5, 9, 22, 26, 32, 36, 45, 52, 59, 66). Taylor 등 (64) 와Tebrock 등 ( 65) 등은의치상의적합도와클래스프설계변화에따른지대치운동을연구하여, 의치상이최대로연장되고잘적합되었을때클래스프설계변화에대한영향은가장적다고보고하였다. Cecconi등 (17) 은클래스프설계의변화가지대치운동에미치는영향에관한연구에서 4종류의클래스프를사용하여지대치운동의방향과크기를측정하였는데, 하중축에서는근심협측으로, 비하중측에서는근심설측으로지대치가주로움직인다고보고하였으며, 또한하중측의지대치운동량은비하중측의지대치운동량보다더크다고보고하였다. 이러한결과는본실험의광탄성모형의응력분포에서보이는바와같이하중측의응력무늬차수가비하중측의무늬차수보다크다는것을관찰하므로써일치한다는것을알수있다. Carlsson 등 (16) 은유리단국소의치를장착한환자의경우, 지대치의동요도가 15% 증가하고장착하지않을경우는 13% 가감소한다고했으며, 또한 12개월동안유리단국소의치를장착하면 65% 의치은염증이발생한것으로보아의치로인한지대치동요도및조직의염증을최소화하기위한국소의치설계가중요하다고보고했다. 윤과장 (3) 은양측성유리단국소의치의설계변화에따른광탄성응력분석에관한연구에서 back-action, R.P.I., Aker s 형의직접유지장치를광탄성분석법을이용하여지대치와인접치및유리단에전달되는응력을분석하였는데, 근심레스트를형성해준 backaction 클래스프와 R.P.I. 클래스프가원심레스트를형성해준 Aker s 클래스프보다다소유리하다고하였으며, 또한 back-action 클래스프는협측에많은응력분포를보이고유리단에서의응력집중현상이가장현저히나타나므로협측과유리단에많은골흡수를야기한다고보고했다. backaction 클래스프의구조를살펴보면근심교합레스트, 원심교합레스트, 유지암, 보상암으로구성되어있고근심설측에서시작하여원심면을돌아근심협측에서끝나게되는것이일반적이며 (2), 유리단국소의치에서 back-action 클래스프를사용할때는지대치에큰외력을전달하므로최후방지대치는적어도두개이상을 splinting (60,61) 하여응력을분산시킬필요가있으며주의깊게계획되고설계제작된국소의치를통해지대치운동을효과적으로줄이고유리단의골흡수를감소시킬수있다고하였다. 그러나 Maxfield 등 (50) 은원심레스트가유리하다고보고했으며 Hend-erson 등 (35) 은근심에이중레스트를설치하는것이유리하다고하였다. 따라서본연구에서는이러한문제점을좀더파악하고자양측성유리단국소의치에서직접유지장치의설계변화즉, mesial connec-tion 과원심레스트를갖는 back-action 클래스프의경우, distal connection 과근심레스트를갖는 backaction 클래스프의경우, mesial connection 과근심레스트를갖는 back-action 클래스프경우, distal connection 과근심레스트및원심레스트를갖는 back-action 클래스프의경우그리고 mesial connection 과근심레스트및원심레스트를갖는 back-action 클래스프의경우인 5가지유형으로분리하여응력분포양상을하중측, 비하중 388

11 측으로나누어비교하고자하였다. 국소의치의응력분석방법은 dial gauge (31, 41, 63), strain gauge (67), 광탄성응력분석 (15, 42, 66), 유한요소법 (69, 70) 등이이용되어왔으며최근에는 stereophotogrammetry (13) 와 laser 를이용한방법도개발되고있다. 본연구에사용된광탄성응력측정법은빛의간섭현상을이용하여변형된물체의응력분포를관찰하는방법을이용하였으며이것은크게두가지방법이이용되고있는데첫번째방법은투과형방법으로서해석대상의물체를빛이투과할수있는투명한광간섭재료로모델을제작하여편광판사이에위치시키면광원으로부터나온빛이첫번째편광판 (polarizer) 를통과함으로써편광판의방향과일치하는편광만빠져나오게되며, 이편광이모델에입사하게되면모델에작용하고있는주변형율의차에비례하여빛이굴절하면서위상지연 (phase retard-ation) 이일어나게되고, 주응력방향으로굴절된빛이두번째놓인편광판에입사되면, 편광축방향의빛만통과되면서빛의간섭을일으키게되며, 두번째방법은빛이투과하지못하는물체의표면응력을검토하는반사형광탄성실험방법으로서빛이물체를통과하지못하므로, 물체의표면에투명한광탄성재료를빛이잘반사될수있는은분말접착제를도포하여물체의표면에서생기는간섭무늬를반사시켜관찰하는방법인데기본원리는투과형방법과동일하나, 빛이표면에도포된광탄성재료에입사되었다가다시반사되어나오기때문에 2회의위상지연이생긴다 (4, 8, 24, 38). 따라서 3차원적인하악골광탄성모형을제작하여투과형으로응력분포를관찰키위해서는모형의 내부에점광원을설치하고, 하악골모형을좌우로회전시키면서, 부분부분의응력분포를관찰해야할것이나, 이방법은장치제작이복잡하며, 응력분포양상을부분적으로만보기때문에한눈에응력분포양상을관찰하기힘든단점이있다 (4). 그러므로본연구에서는두번째방법인반사형광탄성응력측정법 (4, 8, 24, 38) 을이용하여 3차원적인하악골모형의내면에반사가가능한은색분말페인트를도포하여, 모형내에서발생한응력무늬가손쉽게반사될수있게하므로써전면의응력분포양상을한눈에관찰할수있었다. Nally (56) 는양측성유리단국소의치에서지대치를다루는방법에관한연구에서클래스프의종류를 8가지로세분하여지대치와의치의운동량을연구하였는데, mesial connection 과근심레스트를갖는경우와 mesial connection 과원심레스트를갖는경우에가장양호하다고주장했으며, 이는본연구의 Case 1, Case 3에나타난바와같이거의일치하였다. 또한하중측의지대치운동량과비하중측의지대치와의치의운동량을고려해볼때 mesial connection 이 distal connection 에비하여유리하고교합면레스트를비교해보면근심쪽으로위치할수록원심으로이탈하려는경향을감소시키므로보다유리하다고주장했으며, 이는본연구에서 3종류의 mesial conncetion 이 2종류의 distal connection 보다전반적으로유리하게나타난것과일치한다. Back-action 클래스프를사용할경우는본실험의결과에서확증된것같이근심레스트와 mesial connection, 원심레스트와 mesial connection 을갖는 back-action 클래스프가좋은것으로판단되고, Nally (56), Thompson 등 (66), Kratochvil (46), 389

12 McCartney (51) 의주장과일치한다. 또한지대치에레스트 1개가있는경우가근원심레스트가있는경우에비해서더욱유리하다고주장하였는데 (56), 이는본논문의 Case 5 와일치하였다. Swenson 등은근심교합레스트와원심유지부, 유용한주조환형 back-action 클래스프를주장했다 (61). 또한근심레스트와원심레스트를비교해보면, Thompson 등 (66) 은원심레스트를갖는유지장치에서는임상적치관은원심으로이동하고치근단에서는근심으로이동하므로치조골에수평력을유발하고근심레스트를갖는유지장치에서는작용력을수직으로분산한다고하였다. Kratochvil (46) 은교합면레스트의위치와클래스프설계변화에따른지대치운동에대한연구에서원심레스트는치아를후방으로이동시켜서치아동요도증가, 골손실, 교합불균형을초래하고근심레스트는치아를전방으로이동시켜서전방에있는치아와결합하여저항할수있다고보고하였다. 또한 Zach (71) 는국소의치에서근심레스트의장점에관한연구에서근심레스트는악궁에서회전축이전방에위치하므로저작시발생하는 torquing force 가원심레스트에비해적고, 또한연조직에외상이더적으며, 간접유지장치유지력의필요성이더적고, 원심으로탈락하려는힘이더적다고보고했는데, 이러한연구는본연구의 Case 3 와일치하였다. Case 1에서 Case 5까지설계형태에따라교합면레스트하부, 제2 소구치, 제1소구치및하중이작용하는반대편의지대치들에분포되는응력의 pattern이각기조금씩변하는양상을보이고있으며, back-action 클래스프의특징에따라예측되는응력분산형태를검토해보면다음과같다. Case 1 : Mesial connection 과원심레스트를갖는 back-action 클래스프이경우는클래스프에원심레스트가연결되어있으므로클래스프이마치스프링과같은역할을하게되어 I-B의개략도와같이의치상하방의잔존치주조직에응력이주로분포되며잔존치주조직의침하량에따라제2 소구치에 spring force 가수직방향으로원심쪽에편중되어작용하게되므로, 제2소구치에는수직력과원심쪽의회전모멘트 (M1) 가발생하게된다. 1-A 에보인바와같이부연결장치와클래스프와의길이 L과클래스프의단면형상에따라구해지는단면 2차모멘트의크기에따라가상된스프링강성이결정되는데 (K-3EI/L3) 이시뮬레이션스프링이강성이큰경우에는제2소구치에작용하는연직하중이크게되고회전모멘트도크게되는데, 실험결과에의하면제2소구치치근면과치근단에별로큰응력집중부위가발생하지않은것으로보아서스프링강성이별로크지않은상태라고볼수 390

13 있으며, 그결과로작용하중을치주조직에주로받으며, 치주조직의침하량에따라프레임을타고전달된힘이반대편제2 소구치및제1 소구치에까지힘이전달되는것으로판단되어진다. 경우는제2소구치에수직력과모멘트가크게작용하므로지대치가약할때는매우불리한경우이다. Case 3 : Mesial connection 과근심레스트를갖는 back-action 클래스프 그러므로잔존치조골이약한경우에는별로좋지않다. Case 2 : Distal connection 과근심레스트를갖는 back-action 클래스프 이경우는그림 3-B 의힘의개략도에보인것처 이경우는클래스프가 metal mesh frame 에직결되어의치상하방치은, 클래스프및근심레스트에서제2소구치에작용하는하중을지지하는상태이다. 이경우는클래스프와레스트에분포하중이작용되기때문에제2 소구치원심쪽으로약간평향되는분포하중이작용하게되어제2소구치에는수직력과원심방향의모멘트 (M2) 가발생하여제 2소구치를원심방향으로회전하면서침하하게되기때문에치근면주위로는모멘트를지지하는수평응력과수직하중을지지하려는전단응력이발생되며, 치근단에는집중응력이발생되게된다. 따라서이 럼제2소구치에작용하는하중이 metal mesh frame 과근심레스트까지연결된연결절 (L) 에의해제2 소구치근심부에수직력을전달하게되므로제2소구치에는근심쪽으로회전하려는모멘트 (M3) 를받게된다. 그러나제1소구치, 견치가인접되어있기때문에결국작용하중들은각각의치아에분산되므로힘의분산의관점에서매우양호한경우로볼수있다. 이런결과는 Fig.9에서도잘나타나있으며작용하는응력이의치상하방부와제2소구치, 제1소구치, 견치까지고루분산됨을볼수있다. 391

14 Case 4 : Distal connection 과근심레스트및 원심레스트를갖는 back-action 클래스프 Case 5 : Mesial connection 과근심레스트및 원심레스트를갖는 back-action 클래스프 이경우는근심레스트가 metal me-sh frame 에직결되어있으므로, 제2 소구치에작용하는하중이 metal me-sh frame 과원심레스트에주로전달되고근심레스트에는거의작용하지않으므로힘의개략도를그려보면 4-B와같다. 따라서제2소구치에는수직력과원심쪽의회전모멘트 (M4) 가작용하게되어상당히큰응력을받게되며 metal mesh frame 후방부로지지력의중심이약간이동되는경향을보이게된다. 따라서 Fig.11의경우가 Fig.5, 7, 9의경우에비해 0.8 차의무늬차수가 metal mesh frame 후방부쪽으로좀더길게퍼져있음을알수있고, 제2 소구치의치근단을따라서수직응력과굽힘을저항하는수평응력이치근단전후로분포되어있음을알수있다. 이경우는 Case 2의경우처럼제2 소구치에수직력과모멘트가크게작용하므로지대치가약할때는매우불리한경우이다. 이경우는 metal mesh frame 에근심레스트가연결되어있고근심레스트에연결된클래스프에원심레스트가있는상태이므로원심레스트는마치클래스프이스프링역할을하는경우로생각할수있고근심레스트는원심레스트보다더큰강성을갖고있기때문에근심레스트쪽에더큰집중하중이발생하게되어근심쪽으로약한회전모멘트 (M5) 가발생하게될것이다. 따라서응력의분산형태는제2소구치의치근단방향으로상당히큰응력이집중되며회전모멘트의영향으로응력들이제1 소구치, 견치쪽으로약간분산되어지는상태로 Case 3의경우와유사하나제2소구치에더많은지지력을요하는상태이다. 392

15 V. 결론 참고문헌 하악양측성유리단국소의치에서교합면레스트의위치와직접유지장치연결방법변화에따른응력의크기와분포양상을규명하기위하여 epoxy 레진 (PL-1) 과경화제 (PLH-1) 로삼차원적광탄성모형을제작한후, 은색분말제인반사성성질을가진은색분말 (plastic cement-1) 을광탄성하악골모형의내면에도포하여이차원적인반사형광탄성응력측정법을선택하였다. 5종류의실험국소의치를설계제작하고제1대구치의중심와에 12.5kg의편측수직집중하중을가한후 reflective circular polariscope를이용하여광탄성응력분석을한결과다음과같은결론을얻었다. 1. Mesial connection 과근심레스트를갖는 Case 3 경우에서응력의분산효과가가장우수하였다. 2. 근심및원심레스트를갖는 Case 4,5의경우가최종지대치에만은응력분포양상을나타내었다. 3. 일반적으로 mesial connection 을갖는경우가 distal connection 의경우에비하여응력분산효과가더유리하였다. 4. Mesial connection 을갖는 case 1,3,5 인경우에서는근심레스트를가진경우가응력분산효과면에서가장유리하였다. 1. 강승종, 계기성 : 간접유지장치설계변화에따른하악유리단국소의치의광탄성응력분석, 대한치과보철학회지, 28 : 183, 계기성, 가철성국소의치학, 청해사 p 윤성일, 장익태 : 양측성유리단국소의치의설계변화에따른광탄성응력분석에관한연구, 대한치과의사협회지, 23 : 45, 이규칠, 계기성 : 주연결장칠의설계변화에따른하악유리단국소의치의광탄성응력분석에관한연구, 대한치과보철학회지, 29 : 177, 이병태 : clasp 의변형에따른유지가지대치운동에미치는영향에관한실험적연구, 대한치과의사협회지, 14 : 147, 이호용 clast의형태의변화에따라지대치에가해지는수평압력에관한연구, 대한치과의사협회지, 11 : 811, 임순호, 장익태 : 유리단국소의치 clast 설계가지대치운동에미치는영향, 대한치과보철학회지, 25 : 17, 조규종, 김유, 김택 : 차제 body 용접결합부위광탄성적응력에대한연구, 아세아기보, 6 : 53, 조혜원 : 정밀부착형유지장치에따른양측성유리단국소의치의광탄성응력분석, 대한치과보철학회지, 23 : 97, Applegate, O.C. : The partial de-nture 393

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21 =Abstract= A PHOTOELASTIC STRESS ANALYSIS ON THE SUPPOTING STRUCTURE IN THE MANDIBULAR DISTAL EXTENSION REMOVABLE PARTIAL DENTURE WITH VARIOUS DESNGS OF BACK-ACTION CLASPS Soo - Lyoung Lim, D. D. S., M. S. D., Kee - Sung Kay, D. D. S., M. S. D., Ph. D., Yeong - Mu Ko, D. D. S. Department of Prosthodontics, College of Dentistry, Chosun University Department of Dental Materials, College of Dentistry, Chosun University The purpose of this study was to analyze the magnitude and distribution of stress using a photoelastic model from the mandibular distal extension removable partial dentures with the mesial or distal placement of the occlusal rest and the mesial or distal connection in the backaction clasp with the five various designs of the back-action clasp, that is, the mesial connection and the distal rest, the distal connection and mesial rest, the mesial connection and mesial rest, the distal connection and the mesial and distal rest, and the mesial connection,and the mesial and diatal rest. A photoelastic model was made of the epoxy resin(pc-1) and the hardner(plh-1) with the acrylic resin teeth used and was coated with the plastic cement-1 at the lingual surface of the model and then five kinds of the romovable partial dentures on the photoelastic model were set. A unilateral vertical load of 12.5 kg was applied on the central fossa of the first molar with the use of specially designed loading device and the pattern and distribution of the stress of the photoelastic model under each condition was analyzed by the reflective circular polariscope. The following results were obtained : 1. In the back-action clasp with the mesial connection and mesial rest of the case 3, the effect of the stress distribution was the most favorable. 399

22 2. In the back-action clasp with the mesial and distal rest of the case 4 and 5, the stress distribution was more greatly showed in the terminal abutment. 3. Generally, the stress distribution was more favarable in the mesial connection than in the distal connection. 4. In the back-action clasp with the mesial connection of the case 1, 3 and 5, the stress distribution was the most favorable in the mesial rest. 400