대한치과보철학회지 :Vol. 43, No. 1, 2005 하악구치부에서임플랜트배열방식에따른임플랜트지지고정성국소의치의광탄성응력분석 원광대학교치과대학보철학교실 조혜원 김난영 김유리 Ⅰ. 서론부분무치악환자의보철수복을위하여최근많이이용되는방법은임플랜트를이용하여인접지대치를손상하지

대한치과보철학회지 :Vol. 43, No. 1, 2005 하악구치부에서임플랜트배열방식에따른임플랜트지지고정성국소의치의광탄성응력분석 원광대학교치과대학보철학교실 조혜원 김난영 김유리 Ⅰ. 서론부분무치악환자의보철수복을위하여최근많이이용되는방법은임플랜트를이용하여인접지대치를손상하지않고수복하는방법이다. 임플랜트에의한수복은특히하악구치부에서임플랜트의수와길이, 직경등치료계획과보철물제작방법이다양하게제시되고있으며이에따라임플랜트지지조직에서의응력발생양상과분산에대한비교분석이필요하다. 1-3) Lekholm 등 1) 은고정체의수가충분해야골유착을유지할수있고구치부에서두개보다세개의임플랜트를매식하는것이훨씬유리하다고하였고, Rangert 등 2) 은수뿐아니라위치의중요성을강조하였다. 그들은두개의임플랜트가가운데인공치 (pontic) 로연결되어있는경우의응력상태를 100% 라고가정하면, 같은두개라도캔틸레버 (cantilever) 가전방이나후방에있으면 200% 로증가하고, 세개가연결되어있으면 66% 로감소하여세번째임플랜트의존재가매우중요하다고하였다. 또한중간임플랜트를 2-3 mm 정도협측으로이동하는삼각형배열방식 (tripod implant configulation) 을이용하여지지조직에대한응력을낮추라고권고하였다. 보통완전무치악에임플랜트를매식할경우에는 악골의형태에따라곡선상의배열을보이는경우가많으나하악구치부의부분무치악은보다직선상의배열을보이게된다. 3) 임플랜트의위치가직선화될수록레버효과에의한휨모멘트 (bending moment) 가인장력이나압축력보다더큰영향을미칠수있다. 따라서완전무치악보다부분무치악의구치부에서과하중 (overload) 에따른임플랜트주위골의소실혹은각구성부의파절이발생할확률이높다. 그러나하악구치부에서세개의임플랜트를삼각형으로배열하기위해서는악골의형태가보다풍융해야하고협설측교합면을형성할때주의할필요가있다. 4) 또한잘맞지않는보철물이나설계가잘못된보철물에의해응력분산효과가감소할수있다. 5) 상부보철물을제작하는과정에서연결고정 (splinting) 은응력을분산시키는하나의방법으로사용되어왔다. 자연치의연결고정은동요가있는치아에서인접치를이용해안정성의회복과응력분산을목적으로시술되었다. 6) 임플랜트지지수복물에서도인접임플랜트가있는경우에는적절한하중점과하중방향을설정하고교합압을분산시키기위하여서로연결고정하도록권고해왔다. 7,8) 반면연결고정된수복물이수동적으로적합 (passive fit) 되지못하면치경부골소실을야기하며, 지대주나사와 이논문은 2003 년도원광대학교의교비지원에의해서수행됨. 120

임플랜트의파절까지일으킬수있다. 1,2,9) 이에따라부정확하게연결된다수임플랜트보철물대신인접한임플랜트를개별적으로수복하는방법을제안하는임플랜트시스템이증가하고있며, 10) Fischman 11) 은임플랜트로수복할경우, 연결고정된전악보철물을제작하는대신개별적으로수복된보철물을추천하였다. 이상과같이하악구치부에서직선형배열과삼각형배열에대한실제응력분산효과는명확하게검증되지않고있으며, 연결고정의의미와효과를비교하는것은현재혼란스러운보철물제작유형의확립에일조할수있을것이다. 본연구의목적은하악구치부에서두가지다른배열방식에따라매식했을때연결고정을한고정성국소의치와개별수복한고정성국소의치를제작하고, 각고정체에가해지는응력의크기와분산을비교분석하여임플랜트를이용한고정성국소의치의설계에도움이되고자한다. Ⅱ. 연구재료및방법 1) 고정체식립과광탄성모형의제작하악부분무치악을모사하기위해 3 전치가잔존한우측하악구치부의모형을왁스업해제작하였다. 직선상배열모형과삼각형배열모형을만들기위해실리콘몰드 (KE-1300, Shin-Etsu, Japan) 를제작하고두개의경석고모형을제작하였다. 두모형상에서각각써베이어를이용두개의 4.0 13 mm 직경의고정체 (Lifecore, USA) 와한개의 5.0 10 mm 직경의고정체 (Lifecore, USA) 를모형에식립하였다. 이때직선형배열방식에서는세개 의고정체를써베이어를이용해교합면에수직으로배열하였고, 삼각형배열방식에서는전방임플랜트는 0.5 mm 설측으로위치시키고, 중간임플랜트는 1 mm 협측, 후방임플랜트는 1 mm 설측으로경사시켰다.(Fig. 1, 2) 각고정체에인상용코핑을연결하고복제하여실리콘몰드 (KE-1300, Shin-Etsu, Japan) 를제작하였다. 인상용코핑에실제고정체를연결하고, 실리콘몰드에하악골과유사한탄성계수를보이는광탄성레진 (PL-2, Measurements group, USA) 을부어광탄성모형을제작하였다. 동시에임플랜트고정체에인접한하악견치의실리콘몰드를만들어치아와비슷한광탄성레진 (PLM-2, Measurements group, USA) 을부어완성하였다. 각치아와광탄성모형은빛의투과에영향이없을정도로표면을연마하고응력상태를점검하여완성하였다.(Table I) 2) 나사유지형보철물의제작제작된광탄성모형에인상용코핑을이용하여인상을채득하고주모형을경석고로제작한다음모형상에서육각이있는 UCLA 지대주 (Lifecore, USA) 를이용한 3 개의 single crowns를 straight configuration 모형과 tripoding configuration 모형에서각기제작하였다.(Fig. 3, Table II) 보철물은실리콘인덱스를이용해두가지모두외형이같은규격이되도록조정하고고주파주조기를사용하여금합금 (Dongmyung co., Korea) 으로주조하였다. 보철물의적합도는 20배의기공용현미경을이용하여검사하였다. 동시에육각이없는 UCLA 지대주를이용하여 3-unit bridge(dongmyung co., Korea) 를주조적 Fig. 1. Straight configuration. Fig. 2. Tripoding configuration. 121

합하였으며, 수동적합을이루기위해주조후분리하고납착하였다. 연결후 20 Ncm의토오크로고정하였다. Fig. 3. Fabrication of implant supported FPD. 3) 하중장치각금관의교합면에중심와와협설교두, 전방임플랜트의근심와, 후방임플랜트의원심와에하중점을 # 6 round bur로형성하고정하중기와하중구를이용하여각하중점에 80 N의정하중을가하였다. (Fig. 4) Table I. Materials used in this study Mandible PL-2 Measurements USA Teeth PLM-1 Measurements USA Periodontal ligament Solithane Uniroyal Chemical USA Implant 4.0 13 mm 5.0 10 mm Lifecore USA Table II. Experimental groups Groups Fixture arrangement Restoration Abutment 1 Straight Individualized Hexed 2 Straight Splinted Nonhexed 3 Tripod Individualized Hexed 4 Tripod Splinted Nonhexed Lighte Source CCD Speolmen P1 Q1 Q2 P2 P1 : Polsrlzer P2 : Amalyzer Q1, Q2 : Quart - wave plate Computer image Processor Fig. 4. Loading device. Fig. 5. Schematic representation of polariscope principle. 122

4) 광탄성응력분석하중을가했을때발생하는응력은디지털카메라 (S2 Pro, Fuji FinePix, Japan) 를사용하여촬영하였다. 사진상에나타나는광탄성무늬를관찰하고, 각임플랜트에서경부와근단부로나누어 isochromatic fringe characteristics를참조, 무늬차수 (fringe order) 를계측비교하였다.(Fig. 5) Ⅲ. 연구성적 1) 전방임플랜트에하중을가한경우두배열방식모두개별수복한경우에는전방임플랜트에대한하중시후방으로는하중이전달되지않고전방임플랜트에만응력이발생하였다. 전방임플랜트의중심와에대한하중시, 직선형배열에서는개별수복한경우, 전방임플랜트의근단부에서 2차의응력이발생하였다. 연결고정한경우에는 0.5 차이하의낮은응력이근단부에발생하였다.(Fig. 6, 7) 삼각형배열에서는개별수복한경우, 전방임플랜트의근원심치축을따라좀더길게응력이나타났고특히근심측치조정까지길게연장되었다. 연결고정한경우에는근단부에 1 차이하의낮은응력이발생하였다. 연결고정한경우배열방식에상관없이매우약한응력이세개의고정체주위에걸쳐나타났으며, 중간임플랜트의근원심치조정에서미약한응력증가가일어났다.(Fig. 8, 9) 이런현상은주조과정의오차로생각되어분리, 재납착의과정을시행했으나크게개선되지않았으며, 수동적합에어려움이있었던것으로생각된다. 전방임플랜트에대한근심와하중시중심와에대한하중시보다개별수복한경우, 응력의증가와함께근심부로의이동이나타났으며이런경향은임플랜트가약간설측으로위치된삼각형배열방식에서뚜렷하게나타났으나, 연결고정한경우에는전방임플랜트근단부에미약한응력증가를보인것이외에는큰변화는없어연결고정이유리함을나타내었다. 협설교두에대한하중시에는중심와에가한경우와큰차이가없었다.(Fig. 10-13) 2) 중간임플랜트에하중을가한경우중간임플랜트의중심와에하중을가하면, 직선형배열에서는개별수복한경우전후방임플랜트로의응력분산은거의보이지않았으며, 중간임플랜트의근단부에 1차응력이집중되었다. 동시에근원심치조정에도 1 차의응력이발생하였다. 연결고정한경우에는응력집중이없이고르게분산되었으며협설교두에대한하중시미약한응력전달이전방이나후방임플랜트에나타났다.(Fig. 14-17) 삼각형배열에서는중간임플랜트에대한중심와하중과설측교두하중시몸체전반에서 1.5 차정도의응력이발생하며특히설측교두에대한하중시휨모멘트를보였다. 그러나협측교두하중시에는오히려감소하였으며, 이런현상은연결고정시에는거의나타나지않았으나근원심치조정에서약간의응력증가를나타냈다.(Fig. 18-21) 3) 후방임플랜트에하중을가한경우후방임플랜트의중심와에하중을가하면, 직선형배열에서는개별수복한경우근단부에 1 차, 근단부근심측에 0.5 차의응력을발생하였다. 원심와에하중을가하면, 원심근단부의응력이동이일어났으나크게치축방향을벗어나지않았다. 연결고정한경우에는 0.5 차정도의미약한응력이후방임플랜트의근단부에나타났으나응력분산이일어나응력이거의나타나지않았다.(Fig. 22-25) 삼각형배열에서는중심와에하중을가하면, 개별수복한경우응력발생이근단부원심측으로 1.5 차정도발생하였으나후방임플랜트의직경이크기때문에전방이나중간임플랜트보다유리하였다. 원심변연에하중을가한경우 2 차의응력이원심측으로경사되일어났다. 연결고정한경우에는근단부에 1.5 차의응력이나타났으나개별수복한경우보다치축방향을이루고있으며, 협측교두와원심변연에하중시에는 2차로증가하나개별수복한경우보라치축방향을이루어연결고정효과가있는것으로생각된다.(Fig. 26-29) 123

Ⅳ. 총괄및고찰임플랜트수복을필요로하는환자의 70% 이상이부분무치악환자로이들환자를위한치료계획과보철물제작에대해다양한치료방법이제안되고있다. 특히하악구치부의유리단에서는교합압이타부위에비해크기때문에임플랜트로수복하기위해서그수와위치, 배열을결정할때응력분산을고려해설계해야한다. 하악구치부에서세개의치아가결손되었을때두개의임플랜트로수복하기도하나이갈이와같은부기능이있거나교합압이높을것으로예상되면임플랜트의나사풀림이나파절이일어날확률이높아진다. Rangert 등 2) 은임플랜트를매식할때직선상배열 (linear configuration) 보다삼각형배열 (tripod configuration) 이되어야휨모멘트 (bending moment) 에대한보상이가능하다고하였고, Rangert와 Sullivan 3) 도협측이나설측으로치우치게배열하는방법 (offset placement) 이휨을축방향의힘으로변형시켜응력을감소할수있다고하였다. Weinberg 와 Kruger 12) 는이차원에서토크 (torque value) 를계산하여삼각형배열방식의효과를입증하였다. 반면 Taylor 등 4) 은한개의임플랜트를몸체이동할수있을정도로하악골의협설폭이충분하기가어렵고, 약간의각도변경만해서삼각형배열방식을모방하는경우에는바라는효과를얻기가어렵다고하였다. 또한동물실험결과에서도 non-axial loading이임플랜트의골유착에유해하지않음을입증했다. 13) 그러나 Akca 등 14) 은유한요소법을이용한연구에서직선형배열과삼각형배열을비교한결과삼각형배열방식의잇점이없었고세개의임플랜트를연결한고정성국소의치의협측교두에여러개의하중점을두고동시에 400 N을 30 경사방향으로가한결과모든임플랜트의협측지지골에서는인장력이발생하였고설측지지골에서는압축력이발생하였으며최대인장력은전방임플랜트의근심협측, 최소압축력은후방임플랜트의원심설측이었다고보고했다. 본연구에서도하중방법이다르긴하나같은부위에응력이나타났으며연결고정한경우에두가지배열방식의비교결과, 삼각형배열방식과직선형배열방식사이에큰차이가없으나, 직선형배 열방식이오히려몇가지경우에유리한분산을보였다. Itoh 등 15) 도두배열방식사이에응력양상은약간다르나삼각형배열방식이명확하게응력을감소한다는증거가없다고하였다. 특히수직하중이나협측하중시하중위치에관계없이삼각형배열방식에서중간임플랜트에높은응력을발생하였으며, 하중조건에따른차이가많고그차이도 0.5 fringe 이하로매우작아, 두배열방식의우열을가리기가어렵다고하였다. 본연구에서개별수복한경우에는삼각형배열에서는전방임플랜트의근원심치축을따라좀더길게응력이나타났는데, 직선형배열에비해접촉점의위치가다르고휨모멘트가발생하기때문으로생각된다. 삼각형배열방식에서하중부임플랜트의축이장축방향이아니면그에따른응력의증가와모멘트가발생함을알수있었다. 특히협설교두의수직하중시에배열방식에따른차이가있었다. 전방임플랜트의근심와하중시와후방임플랜트의원심와하중시에는배열방식에상관없이큰응력이각하중부의근단부와치조정에나타났다. 하악골에서협측이나설측으로임플랜트를배열하면주위의잔존골의양이얇아져하중에불리할수있다. 본연구에서도삼각형배열시협측위치된중간임플랜트에서과하중의위험성이증가하였다. 임상적연구와실험적연구에의해과하중이골유착을소실하게할수있다고결론지어졌다. 어떤연구에서는응력집중부위에서골흡수가일어남을입증할수있었지만, 실제로골흡수나골재형성과같은생물학적인변화를일으키는응력치는아직알려져있지않다. 9,13) 다만치밀골의최대인장강도 (UTS) 는 121 MPa 이고, 최대압축강도 (UCS) 는 167 MPa로알려져있으며, 본연구에서도직경이넓은임플랜트가후방에서응력감소에효과적임을보여주었다. 14) 본연구에서후방임플랜트는 5.0 mm 10 mm로전방과중간임플랜트보다직경이크고짧은임플랜트를선택하였다. 이는후방구치부에서하치조관때문에긴임플랜트를매식하기어려울때가많아이를반증하기위한것이었다. 후방임플랜트는중심와에대한하중시에는전방과중간임플랜트보다응력발생부위는감소하고근단부에서축방향으로 124

발생하여길이가짧아도직경이넓은고정체가유리함을보여주었다. 그러나원심와하중시에는직선형배열에연결고정한경우을제외하고원심치조정과원심측근단부에응력이발생하였다. 특히삼각형배열방식에서후방임플랜트는약간설측경사되어있으므로원심으로의응력이높게나타났는데, 연결고정한경우에는응력발생부가좀더축방향으로이동하였다. Acka 등 14) 은 3.75 mm와 4.0 mm의임플랜트를비교한결과조금더넓은 4.0 mm 고정체에서응력이감소하고, 또 8 mm 와 10 mm 고정체를비교한결과, 같은직경에서길이가긴것이응력감소에유리하였다고보고하였다. 임플랜트의직경이작으면, 직경이넓은것보다항복강도가낮고길이가짧으면, 긴임플랜트보다골지지도가낮아불리하다. 넓은직경의임플랜트는직경이증가하면서표면적과질량이증가한다. 면적이증가하면서하중이일정하면응력은감소하며, 질량의증가로인접임플랜트에휨모멘트를유발하는수평력에대한저항도증가할것이다. 세개의임플랜트를연결고정한경우에고정하지않고개별수복한경우보다하중을가하지않은상태의응력은다소크게나타났다. 그러나하중이가해지면하중점의위치에따른차이가크게감소하면서세개의임플랜트에보다균등한응력분포를나타냈다. 전방임플랜트에대한하중시에는전방임플랜트의근심측과치조정에응력이높았다. 중간임플랜트로의하중전달은전방과중간임플랜트사이치조정과원심치조정및근단부에나타났다. Ⅴ. 결론하악구치부에서이상의여러변수에따른보철물을제작하고이를연결했을때임플랜트주위에발생하는응력의크기와분포를광탄성응력분석법으로비교하여실제임상에서임플랜트의위치를선택하고수복물제작시주의해야할점과지속적으로주의관찰해야할점등에대한정보를제공하고자하였다. 본연구의결과는아래와같다. 1. 개별수복한경우두배열방식에서하중위치와방향에따라응력양상이다르게나타났으며인접임플랜트로의응력전달은일어나지않았으나연 결고정한경우하중임플랜트에대한응력은감소하면서응력분산이일어났다. 2. 개별수복한경우, 삼각형배열방식이전방임플랜트와중간임플랜트에대한하중시보다불리하게나타났다. 3. 연결고정시에는중심와에대한수직하중시삼각형배열에서후방임플랜트의응력이높았으나, 두배열방식간의차이는거의없었다. 하악구치부부분무치악에서고정성국소의치로연결고정한경우, 삼각형배열방식은직선형배열방식에비해큰차이가없었다. 개별수복한경우, offset 이길어지면서중간임플랜트에서오히려삼각형배열이불리한것으로나타났다. 참고문헌 1. Lekholm U, van Steenberghe D, Herrmann I, Bolender C, Folmer T, Gunne J et al. Osseointegrated implants in the treatment of partially edentulous jaws. A prospective 5-year multicenter study. Int J Oral Maxillofac Implants 1994;9:627-635. 2. Rangert B, Krogh P, Langer B, and Roekel N. Bending overload and implant fracture: A retrospective clinical analysis Int J Oral Maxillofac Implants 1995;10: 326-334. 3. Rangert BR, Sullivan RM, Jemt TM. Load factor control for implants in the posterior partially edentulous segment. Int J Oral Maxillofac Implants 1997;12:360-370. 4. Taylor TD, Agar JR, Vogiatzi T. Implant prosthodontics: Current perspective and future directions. Int J Oral Maxillofac Implants 2000;15:66-75. 5. Kunavisarut C, Lang LA, Stoner BR, Felton DA. Finite element analysis on dental implant-supported prostheses without passive fit. J Prosthodont 2002; 11:30-40. 6. Serio FG. Clinical rationale for tooth sta- 125

bilization and splinting. Dent Clin North Am 1999;43:1-6. 7. Stegaroiu R, Sato T, KusaKari H, Miyakawa O. Influence of restoration type on stress distribution in bone around implants: a three-dimensional finite element analysis Int J Oral Maxillofac Implants 1998;13: 82-90. 8. Landry KE, Jonhson PF, Parks VJ, Pelleu GB Jr. A photoelastic study to determine the location of the nonrigid connector in a five-unit intermediate abutment prosthesis J Prosthet Dent 1987;57:454-457. 9. Hoshaw SJ, Brunski JB, Cochran GV. Mechanical loading of Bra nemark implants affects interfacial bone modeling and remodeling. Int J Oral Maxillofac Implants 1994;9:345-360. 10. Fleming AE. The Endopore dental implant system: Implant treatment simplified. J Can Dent Res 1994;60:785-789. 11. Fischman B. The rotational aspect of mandibular flexure. J Prosthet Dent 1990; 64:483-485. 12. Weinberg LA, Kruger B. An evaluation of torque (moment) on implant/prosthesis with staggered buccal and lingual offset. Int J Periodontics Restorative Dent 1996;16: 252-265. 13. Celleti R, Pameijer CH, Bracchetti G, Konath K, Persichetti G, Visani I. Histologic evaluation of osseointegrated implants restored in nonaxial functional occlusion with preangled abutments. Int J Periodontics Restorative Dent 1995;15:563-573. 14. Akca K, lplikcioglu H. Finite element stress analysis of the influencde of staggered versus straight placement of dental implants.-5 Int J Oral Maxillofac Implants 2001;16:722-730. 15. Itoh H, Caputo AA, Kuroe T, Nakahara H. Biomechanical comparison of straight and staggered implant placement configurations. Int J Periodontics Restorative Dent 2004; 24:47-55. Reprint request to: Hye-Won Cho, D.D.S., M.S.D., Ph.D. Department of Prosthodontics, College of Dentistry, Wonkwang University 344-2, Shinyong dong, Iksan, Jeonbuk, 570-749, Korea hwcho@wonkwang.ac.kr 126

사진부도 1 Fig. 6. Stresses produced by loading on central fossa of anterior implant in G1. Fig. 7. Stresses produced by loading on central fossa of anterior implant in G2. Fig. 8. Stresses produced by loading on central fossa of anterior implant in G3. Fig. 9. Stresses produced by loading on central fossa of anterior implant in G4. Fig. 10. Stresses produced by loading on mesial fossa of anterior implant in G1. Fig. 11. Stresses produced by loading on mesial fossa of anterior implant in G2. Fig. 12. Stresses produced by loading on mesial fossa of anterior implant in G3. Fig. 13. Stresses produced by loading on mesial fossa of anterior implant in G4. Fig. 14. Stresses produced by loading on central fossa of middle implant in G1. 127

사진부도 2 Fig. 15. Stresses produced by loading on central fossa of middle implant in G2. Fig. 16. Stresses produced by loading on central fossa of middle implant in G3. Fig. 17. Stresses produced by loading on central fossa of middle implant in G4. Fig. 18. Stresses produced by loading on lingual cusp of middle implant in G1. Fig. 19. Stresses produced by loading on lingual cusp of middle implant in G2. Fig. 20. Stresses produced by loading on lingual cusp of middle implant in G3. Fig. 21. Stresses produced by loading on lingual cusp of middle implant in G4. Fig. 22. Stresses produced by loading on central fossa of posterior implant in G1. Fig. 23. Stresses produced by loading on central fossa of posterior implant in G2. 128

사진부도 3 Fig. 24. Stresses produced by loading on central fossa of posterior implant in G3. Fig. 25. Stresses produced by loading on central fossa of posterior implant in G4. Fig. 26. Stresses produced by loading on distal fossa of posterior implant in G1. Fig. 27. Stresses Fig 29. Stresses produced by loading on central fossa of posterior implant in G4. Fig. 28. Stresses produced by loading on distal fossa of posterior implant in G3. Fig. 29. Stresses produced by loading on distal fossa of posterior implant in G4. 129

ABSTRACT PHOTOELASTIC STRESS ANALYSIS OF IMPLANT SUPPORTED FIXED PROSTHESES WITH DIFFERENT PLACEMENT CONFIGURATIONS IN MANDIBULAR POSTERIOR REGION. Hye-Won Cho, D.D.S., M.S.D., Ph.D., Nan-Young Kim, D.D.S., M.S.D., Yu-Lee Kim, D.D.S., M.S.D. Ph.D. Dept. of Prosthodontics, College of Dentistry, Wonkwang University Statement of problem. More than 70% of patients who need the implant supported restoration are parially edentulous. The principles of design for implant supported fixed partial denture in mandibular posterior region are many and varied. Jurisdiction for their use is usually based on clinical evaluation. There are several areas of interest regarding the design of implant supported fixed partial denture in mandibular posterior region. 1) Straight and tripod configuration in implant placement, 2) Two restoration types such as individualized and splinted restorations. Purpose. The purpose of this study was to compare the amount and distribution of stress around the implant fixtures placed in the mandibular posterior region with two different arrangements and to evaluate the effects of splinting using the photoelastic stress analysis. Material & methods. 1) Production of study model: Mandibular partially edentulous model was waxed-up and duplicated with silicone and two models were poured in stone. 2) Fixture installation and photoelastic model construction: Using surveyor(ney, USA), 3 fixtures(two 4.0 13 mm, one 5.0 10 mm, Lifecore, USA) were installed in straight & tripod configurations. Silicone molds were made and poured in photoelastic resin (PL-2. Measurements group, USA). 3) Prostheses construction: Four 3-unit bridges (Type III gold alloy, Dongmyung co., Korea) were produced with nonhexed and hexed UCLA abutments and fitted with conventional methods. The abutments were tightened with 30 Ncm torque and the static loads were applied at 12 points of the occlusal surface. 4) Photoelastic stress analysis: The polarizer analyzer system with digital camera(s-2 Pro, Fujifilm, Japan) was used to take the photoelastic fringes and analysed using computer analysis program. Results. Solitary hexed UCLA restoration developed different stress patterns between two implant arrangement configurations, but there were no stress transfer to adjacent implants from the loaded implant in both configurations. However splinted restorations showed lesser amount of stresses in the loaded implants and showed stress transfer to adjacent implants in both configurations. 130

Solitary hexed UCLA restoration with tripod configuration developed higher stresses in anterior and middle implants under loading than implants with straight configurations.splintied 3 unit fixed partial dentures with tripod configuration showed higher stress development in posterior implant under loading but there were no obvious differences between two configurations. Conclusions. The tripod configuration of implant arrangement didn t show any advantages over the straight configuration. Splinting of 3 unit bridges with nonhexed UCLA abutments showed less stress development around the fixtures. Solitary hexed UCLA restoration developed tilting of implant fixture under offset loads. Key words : Photoelastic stress analysis, Straight configuration, Tripod configuration, Wide diameter implant, Splinting 131