대한치과보철학회지 :Vol. 41, No. 2, 2003 공진주파수분석법에의한임플랜트의안정성측정에관한연구 단국대학교치과대학보철학교실 박 철 임주환 조인호 임헌송 Ⅰ. 서론골지지성골내임플랜트는악안면, 치과및정형외과영역에서점차사용이증가되고있다. 식립후이러한임플랜트는주위의골과밀접한결합 (union) 이형성되며이것을골유착 (osseointegration) 이라한다. 1-4) 임상적으로임플랜트는 90% 의높은성공률을보이지만골질이나쁘거나, 조직이손상된곳에서는임플랜트는현저한성공률의감소를보인다. 65,6-9) 임플랜트의안정성과골유착의임상적측정은임플랜트의성공여부를평가하는데중요하다. 10-13) 임플랜트의안정성은식립시일차안정성과골치유와골형성결과에의한이차안정성으로구분할수있으며, 일차안정성은임플랜트식립부위의골질과골량, 임플랜트의길이, 직경, 형태, 식립방법에따라영향을받는다. 5-7) 지금까지임플랜트식립시초기안정성의측정은경험적이고, 주관적이었다. 따라서매식체식립시에초기안정성과기능시임플랜트의상태를모니터링하는것이가능하고, 정량적으로정확하게측정할수있다면임플랜트의디자인을각각의환자에게최적으로적합하게개량해줄수있으며임플랜트의실패율을줄일수있을것으로사료된다. 이러한임플랜트의안정성을객관적으로수치화하여평가하는방법으로 Shulte 14,15) 에의해서 Periotest 가개발되어임플랜트의동요도를측정함으로써보철물을장착하기전, 치유기간이더필요한지의여부를결정하는데도움을줄수있었다. 그러나이기술은지 대치에대한각도와높이, 임플랜트와측정 rod 사이의거리에민감하다. 16) 따라서생체내에서임플랜트의안정성을정량적으로측정하기위한가역적인실험법을개발하기위해 Meredith 등 10-13) 은특정주파수범위에서주파수를고주파에서저주파혹은저주파에서고주파로연속적으로변화시킨정현파 (sine wave) 를일정한진폭으로가진하는공진주파수분석장치를개발하였다. 이방법은지대주혹은지대치에부착된작은변환기를이용하여공진주파수를측정하게된다. 공진주파수는임플랜트-조직계면의견고도와유효지대주길이에영향을받고, 식립시기의골질, 치유기간동안골의견고도의변화, 임플랜트주위변연골높이의변화를반영하며, 임플랜트식립후의안정성변화측정을가능하게해준다고보고하였다. 10,12) 본연구에서는 Meredith에의해개발된공진주파수측정장치가가지는단점을극복하고균일한측정치를반복적으로재현가능하면서안정된측정데이터가빠른시간내에처리될수있는공진주파수측정장치를개발하였다. 또한변환기에가해진잔류응력이균일한측정에방해를주는요소이므로잔류응력의제거여부를확인할수있는장치를부착하여측정장치의안정성을증가시켰다. 이공진주파수측정장치를이용한생체외실험을통해다른가역적안정성측정방법과비교하여측정장치의안정성을분석하였고, 임플랜트-조직계면의견고도와유효지대주길이가공진주파수와상관관계가있음을검증하였으며, 생 182
체내실험을통해임플랜트식립후시간경과에따른안정성변화측정을하여다소의지견을얻었기에이에보고하는바이다. Ⅱ. 실험재료및방법 1. 실험재료및기구 (1) 임플랜트전체가선반가공되어평활한표면을가지고있는 CP Titanium(Grade Ⅱ) Machined Screw Implant(SooMin Co., KOREA) 를총 72개사용하였다. 직경은모두 3.75 mm 이었고, 길이는 10mm 가 38개, 13mm가 22개, 7mm, 8.5mm, 11.5mm, 15mm, 18mm, 20mm가각각 2개씩으로 12 개가사용되었다. (2) 임플랜트포매재료 1) Epoxy Resin JRA-323 (Jung Do Co., KOREA) 2) PL-2 Photoelastic Resin (Photoelastic Division Measurement Group Inc. N.C., USA) 3) Hot Melt Adhesive (EVA)(Oh Sung Co., KOREA) (3) 골시편신선한우늑골을폭경 10~15mm, 길이 60~70mm 로 10 개의시편을제작한후임플랜트식립부위의피질골두께가 2~3mm가되도록조절하였다 (Fig.1). (4) 골천공에사용된 Drill Kit 임상에서통상적으로사용되는다음과같은 Drill 을사용하였다. (5) 실험동물체중 4kg 이상의성숙한뉴질랜드산가토 16마리를사용하였다. 가토들은분리된장소에서표준식이로사육되었다. (6) Dynamometrical Contra Angle & Torque Driver (Anthogyr CO., FRANCE) 트랜스듀서를지대주에연결시항상일정한실험 조건을부여하기위해 20 Ncm 의 torque driver를이용하여고정하였다. (7) 지대주유효지대주길이에따른공진주파수의변화량을측정하기위해지대주의길이차이를실제임상에서사용되고있는 3, 4, 5.5, 7, 8.5, 10mm로조건을부여하여트랜스듀서의연결이가능하도록지대주나사상부의형태를변형하였고 CP Grade II 타이타늄 (Dynamet Specialty Metal Products, USA) 재질로제작하였다 (Fig. 2). (8) Periotest (Siemens AG, Benshein, Germany) 치주인대의 damping 효과를기본원리로하고 contact time을정량적으로측정하여치아동요도를나타내기위해고안된전자기구로임플랜트안정성연구에도많이이용된다 (Fig. 3). 14,15) 본실험에서는공진주파수측정장치의측정데이터에대한신뢰성을검증하기위해사용되었다. (9) 공진주파수측정장치 (Resonance Frequency Analyser) 1) 트랜스듀서 (Transducer) 트랜스듀서는 CP Grade Ⅱ 타이타늄재질로지대주와연결이용이하도록캔티레버빔을변형, 응용하여폭 5mm, 높이 10mm 그리고두께는각각 0.5mm, 1.0mm, 2.0mm를갖는타이타늄 zig를밀링기계 (HASEGAWA-HPF, Hasegawa Machine Works., JAPAN) 를이용하여정밀선반가공한후타이타늄 zig 두께의정확성검증을위해 Profile Projector V-12A(Nikon Co., JAPAN) 로정밀도검사를시행하였다 (Fig. 4). 타이타늄 zig의상부와동일한크기 ( 폭 5mm, 높이 10mm) 로가공된 Piezo ceramic element를 Metech(Silver Epoxy) Conductive Adhesive 6090 A & B(Electronic Materials Technology,, USA) 를이용하여타이타늄 zig의상부앞뒷면에접착하였다. 제조회사의지시에따라실온에서 24시간의 adhesive의소성기간을거친후타이타늄 zig와 piezo ceramic element 간의비전도성테스트를시행하였다. 완성된트랜스듀서의두께차이에따른공진주파수영역을분석하여효과적이고안정된측정 183
Table I. Material Properties of FEM. Materials Density(g/mm 3 ) Young's Modulus of Elasticity(kg/mm 2 ) Poisson's Ratio Cancellous Bone(75%) 9.75E-4 5.8E+1 0.30 Compact Bone(75%) 9.75E-4 1.4E+3 0.32 Titanium 4.51E-3 1.05E+04 0.30 4) Power & Charge Amplifier 개인용컴퓨터에서발생한디지털신호를증폭하거나트랜스듀서에서발생한전하량을증폭시키기위한장치를제작하였다 (Fig. 6). 2. 유한요소법을이용한예비실험 Fig. 7. Design of Transducer. 치영역을재현할수있도록고안하였다. 2) Piezo ceramic element Piezo ceramic element는전기적신호를주었을때그것을물리적신호인진동으로바꾸거나물리적신호인진동이들어왔을때전기적신호인전하로바꾸는특성을가진 ceramic 물질이다. Plate를가진할때경량구조물에대해가진하는경우는 piezo ceramic element를사용하고큰물체에대해서는 shaker를사용한다 (Fig. 5). 3) NI-DAQ Version 6.51 (National Instruments, USA) Data Acquisition Driver Software를이용하여개인용컴퓨터에서발생한디지털신호를아날로그신호로변환하거나, 증폭기에서발생한아날로그신호를디지털신호로변환시키는장치이다. 특히고유진동수를알기위한가장좋은방법은망치로대상물을치는것인데, 이에가장근접한방식이 impulse 방식으로사료되어본논문에채택하였다. 해석적인방법을이용하여체적형상의설계변수를예측하기위한목적으로유한요소법을이용하게되는데본연구의실험에앞서제작할트랜스듀서에대한설계를하였다. 진동학분야에서일반적으로알려져있는 mechanical vibration model중에하나인 cantilever beam의형태를응용하여 20) 물성체의특성을잘반영할수있도록높이 10mm, 폭 5mm 그리고두께는 0.5mm, 1mm, 2mm로각기다르게설계하였다. 인체의하악에임플랜트가식립된상태를가상하여 mesh 구조를 modeling하여유한요소모델을설계하였다 (Fig. 7). 25) 분석에필요한탄성계수와 Poisson s ratio 등의물리적성질은선학들의보고를기초로하여사용하였다 (Table I). 상기조건을사용하여 3개의삼차원유한요소모형을설계하였으며, 설계된모형은 8절점입방체요소 (8 node brick element) 로이루어지는선형 (linear) 및등방성 (isotronic) 물체로간주하여분석을시행하였다. 상기조건의구조물의역학적해석을위한유한요소프로그램은 workstation용프로그램인 ANSYS V5.5(ANSYS Co., USA) 를사용하여 Workstation HP C240 (Hewlett Packard Co., USA) 상에서시행하였다. Cantilever beam에 impulse 기법으로가진하여물성의변화에따른진동모드와그에따른주파수를측정하였다. 예비실험의결과를보면두께 0.5mm의트랜스듀서에서는진동모드가약하게변화하였고, 주파수영역이 5,000Hz미만에서분포하는양상을보였다 (Fig. 8, 9). 184
Fig. 14. Components and flow chart of resonance frequency analyser. Fig. 15. Components of transducer. 두께 1mm 트랜스듀서에서는진동모드가확연히변화하였고, 주파수영역이 5,000Hz에서 10,000Hz 사이에분포하는양상을보였다 (Fig. 10, 11). 두께 2mm 트랜스듀서에서는진동모드가심하게변화하였고, 주파수영역이 10,000 Hz 이상의영역에분포하는양상을보였다 (Fig. 12, 13). 이상의결과를바탕으로선학들의보고를참조하여 1mm 두께의트랜스듀서가공진주파수측정에적합한영역을나타내는것으로사료되며, 본논문의실험에서트랜스듀서의두께를 0.5mm, 1mm, 2mm로제작후생체외실험의시편상에서예비실험결과와유사한공진주파수가측정되는지를비교검토하였다. 가감지해서진동을전기적신호로바꾼다. 전기적신호가전하 (charge) 이기때문에이를 voltage로바꾸기위해 Charge Amplifier로입력된다. Voltage로바뀌어진신호는 A/D Converter를통해서디지털신호로바뀌게된다. 이디지털신호를개인용컴퓨터가인식해서주파수분석또는진폭을추출하게된다 (Fig. 14). 트랜스듀서는매식체위에지대주나사를이용하여지대주와연결한다 (Fig. 15). 가진방식으로는큰물체 ( 집이나교량등 ) 에대해서가진기혹은 impact machine이이용되고, 2`~3m 이내의작은물체에대한가진방식으로는다음과같은세가지가있고 17-20,52) 본논문에서는 impulse (impact) 가진방식을적용하였다. 3. 실험장치구성공진주파수측정장치를제작하기위해실험장치구성도를설계하였다. 구성도의원리를보면개인용컴퓨터가가진방법을선택해서컴퓨터내에서디지털파형을발생시키고이를 D/A Converter로보낸다. D/A Converter는디지털파형을전압인아날로그파형으로변화시킨다. 이를 Power Amplifier를통해전압을증폭시키고증폭된전압을 piezo ceramic element로보낸다. Piezo ceramic element는전기적신호를진동으로바꿔서그진동이가진을하게되고가진된상태에서진동이트랜스듀서를흔들게된다. 트랜스듀서의주변환경에따라특정한반응으로서진동의진폭변화를일으킨다. 진폭변화가된진동은다시 piezo ceramic element (1) Sine Sweep 특정주파수범위에서주파수를고주파에서저주파혹은저주파에서고주파로연속적으로변화시킨 sine wave를일정한진폭으로가진한다. 그응답으로서각각의가진주파수에대하여진동고유응답으로서진폭변화를일으키게되고, 그진폭변화를측정하여주파수응답으로사용한다 (Fig. 16). 장점은한주파수에대하여가진파워를가장크게낼수있다는점이고, 단점은전원노이즈나외부노이즈에매우민감하기때문에외부노이즈를제거시키기위하여여러번의평균을취하게됨으로써시간이많이걸리게된다. 외부노이즈를제거하기위한다른방법은측정치에대한 curve fitting과 filtering 과정이며, 이또한시간이많이소요되고, 최종적인측정치를불안정하게만드는요소가된다 17-20,52). 185
(2) White Noise 모든주파수성분을갖는노이즈를발생시켜진동의신호원으로사용한다. 그응답으로서는각주파수에해당되는진폭변화를일으킨 white noise 가된다. 처리는측정된 white noise를 Fast Fourier Transform (FFT) 를통하여주파수 data로변환시킨다 (white noise의의미는모든광원을혼합하면백색광이된다는의미이다 )(Fig. 17). 장점은짧은시간에다양한주파수를가진할수있다는점이고, 단점은 FFT 로처리하는과정이시간이걸리고, 가진하는 white noise의주파수성분이일정치않기때문에측정평균횟수를 sine wave에비해서는적지만많이취해야한다는점이다. 17-20,52) (3) Impulse (Impact) 본논문에적용한방식으로가진원은폭이매우적은 pulse 신호를사용한다. Impact pulse 신호는주파수로변환시키면완전하게평탄한주파수특성을얻을수있다. 또한 pulse 신호하나를보내면전주파수로가진된다. 그응답은 impulse response로트랜스듀서와그주변환경을모두포함한다. Impulse response를가지고주파수변환을시키게되면트랜스듀서및주변환경의물성체특성을정확히분석할수있다 (Fig. 18). 장점은주변 noise에매우강하기때문에측정치가정확하다. 따라서관측된데이터가세가지가진방법중가장뛰어나지만, 많은파워를낼수없어파워앰프가반드시필요하다는점과 impulse 방식을사용하기위한프로그래밍이까다롭다는단점을가지고있다 17-20,52 ). 4. 실험방법트랜스듀서는지대주와연결이용이하도록캔티레버빔을변형, 응용하여제작하였다. 캔티레버빔은폭 5mm, 높이 10mm로두께는 0.5mm, 1.0mm, 2.0mm로제작하여트랜스듀서의두께차이에따른공명주파수영역을분석하여안정된측정치를재현할수있도록하였다. 타이타늄 zig 의상부앞뒤면과동일한크기로가공된 piezo ceramic element를 Metech (Silver Epoxy) Conductive Adhesive 6090 A&B를이용하여부착하였다.. 나사형골유착티타늄임플랜트와지대주를연결한상부에트랜스듀서를장착하여공진주파수를측정하였다. 측정된공진주파수는임플랜트계면에서의강직도 (stiffness) 의변화와그것에대항하는감퇴 (damping) 측정치와의관계를나타내고입력된힘에대한출력응답의비율을측정하여진동수응답곡선을그려낼수있다. 다른실험조건으로는지대주의길이차이를실제임상에서사용되고있는 3.0, 4.0, 5.5, 7.0, 8.5, 10.0mm로조건을부여하여노출된길이즉 effective length에따른공진주파수의변화량을측정하고자하였다. (1) in-vitro 실험 1) 에폭시레진시편공진주파수분석장치의검증을위한실험시편은각 3종류의포매재료를이용하고, 5가지의다른실험조건을부여하기위해다음과같이실험시편을제작하였다. 직경 3.75mm, 길이 13.0mm의선반가공된나사형임플랜트를노출량이동일하게포매하기위해알루미늄소재를이용하여금속주형을선반가공하여제작하였다 (Fig. 19). 공진주파수분석장치의성능검증과측정치에대한정확성과일정성을검증하기위해동일한크기의임플랜트 9개를상부의노출량이동일하도록 Hot Melt Adhesive(EVA) 에포매하였다 (Fig. 20). 공진주파수분석을시행하는데정확한동일실험조건부여를위해 Contra Angle & Torque Driver 를이용하여 20Ncm로트랜스듀서와지대주를임플랜트에고정하였고각지대주에대해 10회씩측정하였다. 또한가로 40mm, 세로 10mm, 높이 30mm의금속시편을선반가공하여제작한후시편제작시필요한 silicone mold (Extrude Polyvinyl siloxane Impression Material Type 2 : KERR Co., U.S.A.) 를제작하여 PL-2 Photoelastic Resin (Photoelastic Division Measurement Group Inc. N.C., USA) 시편을제작하였다. PL-2는인체의피질골경도와유사한물성치를가진다. 완성된블록에통법에따른천공을시행한후지름 3.75mm, 길이 13.0mm의선반가공된나사형임플랜트 9 개를 0~8mm가각각 186
노출되도록식립하여 10 회씩측정하였다 (Fig. 21). 다른시편에서는각기길이가다른임플랜트 ( 지름 3.75mm, 길이 7, 8.5, 10, 11.5, 13, 15, 18, 20mm) 를역시통법에따라천공을시행한후식립하여 10 회씩측정하였다 (Fig. 22). 임플랜트의길이에따른차이를측정하기위해길이 7, 8.5, 10, 11.5, 13, 15, 18, 20mm인선반가공된나사형임플랜트를선반가공된알루미늄금속주형에고정시킨후 Epoxy Resin JRA-323에포매하여공진주파수를각 10회씩측정하였다 (Fig. 23). 또한임상에서문제가되는임플랜트의노출량에따른안정성영향평가를위해지름 3.75mm, 길이 13.0mm의선반가공된나사형임플랜트 9개를 0~8mm 가각각노출되도록주형을제작하여 Epoxy Resin JRA-323에포매하여공진주파수를각 10회씩측정하였다 (Fig. 24). 2) 희생된동물뼈시편희생즉시채취한신선한우늑골을피질골두께 2 3mm, 폭경 10 15mm, 길이 60 70mm의조건에맞도록 10개의시편을준비하였다. 선학들의보고를참조하여, 각시편들은골조직의영계수 (Young s modulus) 감소를 2% 이내로하기위해서 50% ethanol/ saline 용액에담가두었다. 26,27) 23 실온에서 3시간동안유지하였으며, 수분을유지하기위해식염수를적신거즈로덮어두었다. 인체에서피질골이얇은상악구치부의골질을재현하기위하여식립부위의피질골을균일하게 2~3mm를남기고삭제하였다. 임플랜트식립부위는제조회사의지시에의해표준화된수술방법에따라우늑골에천공하였다. 각시편당선반가공된임플랜트를 1개씩총 10개의임플랜트를식립하여트랜스듀서를수직, 수평방향으로장착하여공진주파수를 10회씩측정하였다 (Fig. 25). Periotest value (PTV) 의측정은임플랜트식립시골시편상부에서 4mm 상방지점의 fixture mount 에서시행하였으며, Tricio 등 27) 의보고를참조하여 Periotest 의핸드피스를수평으로유지하였고손잡이는 fixture mount에수직으로, 4mm 이상떨어지지않도록하였으며각각의임플랜트에대하여같은높이에서수직, 수평두방향으로 3회반복시행하였 다. 측정값이 ±1이상벗어나지않은경우그값의평균값을얻었고그렇지않은경우에는반복측정하였다 (Fig. 26). (2) in-vivo 실험분리된장소에서표준식이로사육된 4kg 이상의성숙한뉴질랜드산가토 16마리를사용하였다. 가토의경골에지름 3.75mm, 길이 10mm의 machined surface의나사형임플랜트 16개를마리당 1개씩식립하였다 (Fig. 27). 식립직후트랜스듀서를수직, 수평방향으로장착하여각 3회씩측정하였다 (Fig. 28). 시간의경과에따른공진주파수의변화를측정하기위해식립즉시, 4주, 8주, 12 주, 16 주에식립된부위를절개하여공진주파수를측정하였다. (3) 통계처리본논문의통계처리는 Windows용 SPSS V8.0 (SPSS Inc., USA) 을사용하였다. 각측정값들이정규분포를이루는지조사하기위하여 K-S test를시행하였고, 조건에따른각군의유의성 (p<0.01, p<0.05) 을조사하기위해 one-way ANOVA test와 Correlation test를시행하였다. Ⅲ. 실험결과 1. in-vitro 실험결과 (1) 에폭시레진시편 1) 실험조건 1 : 동일길이에따른비교 (Hot Melt) 길이 10mm 임플랜트를동일한노출량으로포매하여각임플랜트, 지대주에대해 10회씩공진주파수를측정하였다 (n=9). 지대주의길이가 3mm인경우공진주파수가 5953.00Hz를나타내었고, 지대주의길이증가에따라공진주파수가점차감소되는경향을보였으며, 지대주길이가 10mm인경우 4967.56Hz를나타내었다 (Table II, Fig. 29). One-way ANOVA test와 Scheffe a test 결과지대주의길이가증가함에따라공진주파수가유의성있게감소되는양상을보였다 (p<0.01)(table III, IV). 187
Table II. The mean & standard deviation of resonance frequency value according to abutment length. (unit : Hz) Abutment Mean Std. N Length (Unit : Hz) Deviation 3.0mm 5953 9 99 4.0mm 5784 9 175 5.5mm 5587 9 157 7.0mm 5333 9 113 8.5mm 5289 9 110 10.0mm 4967 9 43 Fig. 29. The value of resonance frequency according to abutment length (Hot Melt). Table Ⅲ. The result of one-way ANOVA test of resonance frequency according to abutment length(hot Melt). Sum of Squares df Mean Square F Sig. Between Groups 5838276.31 5 1167655.26 75.749.000 Within Groups 739910.222 48 15414.796 Total 6578186.54 53 (p<0.01) Table Ⅳ. The result of Scheffea test of resonance frequency according to abutment length(hot Melt). Abutment Subset for alpha =.01 Length N 1 2 3 4 10 9 4967.5556 8.5 9 5289.2222 7 9 5333.000 5.5 9 5587.7778 4 9 5784.8889 5784.8889 3 9 5953.0000 sig. 1.000.989.062.165 2) 실험조건 2 : 노출량에따른비교 (PL-2, JRA Epoxy Resin) 길이 13mm 임플랜트를 0mm에서 8mm까지 1mm씩증가시키며노출하여포매및식립후각임플랜트, 트랜스듀서, 지대주에대해 10회씩공진주파수를측정하였다. 트랜스듀서의두께가 0.5mm인경우지대주길이가증가되고임플랜트의노출량이증가할수록주파수영역이주로 5,000Hz 미만에서분포하는양상을보였고, 공진주파수가유의성있게감소하였다 (p<0.01)(table V, Fig. 30). 트랜스듀서의두께가 1mm인경우지대주길이가증가되고임플랜트의노출량이증가할수록주파수영역이주로 5,000Hz에서 10,000Hz 사이에분포하는양상을보였고, 공진주파수가유의성있게감소하였다 (p<0.01)(table V, Fig. 31). 트랜스듀서의두께가 2mm인경우지대주길이가증가되고임플랜트의노출량이증가할수록주파수영역이주로 10,000Hz 이상에서분포하는양상을보였고, 공진주파수가유의성있게감소하였다 188
Table Ⅴ. The result of correlation test of resonance frequency according to abutment length, exposure length of implant embeded into epoxy resin and transducer thickness. Transducer Abutment Fixture Thickness Length Exposure Length RF Transducer Pearson Correlation 1.000 0.000 0.000 0.907** Thickness Sig. (2-tailed). 1 1.000 0.000 N 27 27 27 27 Abutment Pearson Correlation 0.000 1.000 0.000-0.183 Length Sig. (2-tailed) 1.000. 1.000 0.360 N 27 27 27 27 Fixture Pearson Correlation 0.000 0.000 1.000-0.280 Length Sig. (2-tailed) 1.000 1.000. 0.157 N 27 27 27 27 Pearson Correlation 0.907** -0.183-0.280 1.000 RF Sig. (2-tailed) 0.000 0.360 0.157. N 27 27 27 27 (p<0.01) Fig. 30. The value of resonance frequency according to abutment length and exposure length of implant embeded into epoxy resin with 0.5mm thickness transducer. Fig. 31. The value of resonance frequency according to abutment length and exposure length of implant embeded into epoxy resin with 1mm thickness transducer. (p<0.01)(table V, Fig. 32). 따라서실험에적합한트랜스듀서의두께는유한요소법을이용한예비실험에서의결과에서와마찬가지로 1mm인것으로사료된다. 트랜스듀서의두께가 1mm인경우 PL-2에노출량이다르게식립된임플랜트의공진주파수측정시공진주파수가 4069Hz에서 7142Hz까지분포하였고 (Table VI, Fig. 33), correlation test 결과지대주길이와임플랜트의노출량이증가함에따라공진주파수가유의성있게감소하였다 (p<0.01)(table VII). 또한트랜스듀서의두께가 1mm인경우에폭시레진 에노출량이다르게식립된임플랜트의공진주파수측정시공진주파수가 5135Hz에서 9151Hz까지분포하였고 (Table VIII, Fig. 34), Correlation test 결과지대주길이와임플랜트의노출량이증가함에따라공진주파수가유의성있게감소하였다 (p<0.01)(table IX). 3) 실험조건 3. : 재료의물성차이에따른비교 (Hot Melt, PL-2, JRA Epoxy Resin) 7, 8.5, 10, 11.5, 13, 15, 18, 20mm의임플랜트를동일한노출량으로포매및식립하여각임플랜 189
Fig. 32. The value of resonance frequency according to abutment length and exposure length of implant embeded into epoxy resin with 2mm thickness transducer. Fig. 33. The value of resonance frequency according to abutment length, exposure length of implant and transducer thickness(pl-2). Fig. 34. The value of resonance frequency according to abutment length, exposure length of implant and transducer thickness (Epoxy Resin). (2) 희생된동물뼈시편희생된동물뼈시편의공진주파수측정결과지대주의길이가증가함에따라 6355Hz에서 8515Hz의분포를보였고 one-way ANOVA test 결과공진주파수가유의성있게증가되었고 (p<0.05), PTV 결과도지대주의길이가증가함에따라 -5.18에서 4.50의분포를보였으며측정치가유의성있게증가되었다 (p<0.05). 트랜스듀서의측정방향에따른공진주파수측정치와 PTV 결과는유의성있는차이를보이지않았다 (Table XI-XIII, Fig. 37,38). 2. in-vivo 실험 트, 트랜스듀서, 지대주에대해 10회씩공진주파수를측정하였다. 트랜스듀서의두께가 0.5mm인경우물성체의경도차이와지대주의길이가증가함에따라 correlation test 결과공진주파수가유의성있게감소되었다 (p<0.05)(table X, Fig. 35). 또한트랜스듀서의두께가 1mm인경우물성체의경도차이와지대주의길이가증가함에따라 correlation test 결과공진주파수가유의성있게감소되었다 (p<0.05)(table X, Fig. 36). 트랜스듀서의두께차이에따른공진주파수의 correlation test 결과는유의성있는차이를보였다 (p<0.01)(table X). 가토의경골에임플랜트매식후식립즉시, 4주에서 16주까지 4주간격으로트랜스듀서를, 우늑골과평행및직각되는두방향으로장착하고공진주파수를측정한결과 5885Hz에서 6452Hz까지의측정범위를나타냈으며, one-way ANOVA test와 Scheffe a test 결과 4주에서 8 주간을제외하고시간의경과에따른공진주파수의유의성있는차이를보였다 (p<0.05)(table XIV~XVI, Fig.39). 공진주파수측정장치의모니터에나타나는피크의최대치가측정하고자하는대상물의고유진동수이고, 트랜스듀서를장착시가해지는조임력의잔류응력이공진주파수에영향을미치게되므로응력의제거여부를알기위한장치를프로그래밍하여측정 190
Table VI. The mean & standard deviation of resonance frequency value according to abutment length (PL-2). (unit : Hz) Abutment Length Mean Standard 3mm 4mm 5.5mm 7mm 8.5mm 10mm Deviation 0mm 7142 6938 6886 6678 6625 5178 6574 709 1mm 6782 6730 6678 6625 5217 4956 6164 840 2mm 6573 6521 6525 6417 5217 5112 6060 696 Exposure 3mm 6312 6252 6104 6478 5112 4904 5860 674 Length 4mm 6521 6469 6365 6260 4747 4539 5816 916 of 5mm 6260 6208 5686 5165 4226 4591 5356 842 Implant 6mm 5843 5739 5634 5112 5112 4486 5321 515 7mm 5739 5686 5582 4747 4591 4330 5112 626 8mm 5634 5582 5530 4591 4382 4069 4964 697 Mean 6311 6236 6110 5785 5025 4685 Standard Deviation 504 480 522 862 704 374 Table VII. The result of correlation test of resonance frequency according to abutment length, exposure length of implant and transducer thickness (PL-2). Abutment Fixture Length Exposure Length RF Abutment Pearson Correlation 1.000 0.000-0.932 Length Sig. (2-tailed). 1.000 0.000 N 54 54 54 Fixture Pearson Correlation 0.000 1.000 0.142 Length Sig. (2-tailed) 1.000. 0.306 N 54 54 54 RF Pearson Correlation -0.932 0.142 1.000 Sig. (2-tailed) 0.000 0.306. N 54 54 54 (p<0.01) Table VIII. The mean & standard deviation of resonance frequency value according to abutment length (Epoxy resin). (unit : Hz) Abutment Length Standard 3mm 4mm 5.5mm 7mm 8.5mm 10mm Mean Deviation 0mm 9151 9007 8033 7829 7219 6914 8025 911 1mm 8745 8084 7423 7040 6833 6315 7406 883 2mm 7829 7575 7372 6884 6626 6152 7073 631 Exposure 3mm 7524 7270 7040 6729 6522 6203 6881 490 Length 4mm 7169 7067 6864 6522 6419 6050 6681 427 of 5mm 7118 6988 6677 6407 6253 5898 6556 461 Implant 6mm 6660 6574 6419 6203 5898 5389 6190 479 7mm 6470 6263 6056 5901 5694 5338 5953 405 8mm 6470 6304 6203 5948 5338 5135 5899 544 Mean 7459 7236 6898 6607 6311 5932 Standard Deviation 965 888 640 603 586 562 191
Table IX. The result of correlation test of resonance frequency according to abutment length, exposure length of implant and transducer thickness(epoxy Resin). Abutment Fixture Length Exposure Length RF Pearson Correlation 1.000 0.000-0.607** Abutment Length Sig. (2-tailed). 1.000 0.000 N 54 54 54 Pearson Correlation 0.000 1.000-0.747** Fixture Sig. (2-tailed) 1.000. 0.000 Exposure Length N 54 54 54 Pearson Correlation -0.607** -0.747** 1.000 RF Sig. (2-tailed) 0.000 0.000. N 54 54 54 Fig. 35. The value of resonance frequency according to abutment length and stiffness of embedding material with 0.5mm transducer thickness. Fig. 36. The value of resonance frequency according to abutment length and stiffness of embedding material with 1mm transducer thickness. Table X. The result of correlation test of resonance frequency according to abutment length, stiffness of specimen and transducer thickness(epoxy Resin). Transducer Abutment Thickness Length Stiffness RF Transducer Pearson Correlation 1.000 0.000 0.000 0.919** Thickness Sig. (2-tailed). 1.000 1.000 0.000 N 27 27 27 23 Abutment Pearson Correlation 0.000 1.000-1.000** -0.456* Length Sig. (2-tailed) 1.000. 1.000 0.029 N 27 27 27 23 Stiffness Pearson Correlation 0.000-1.000** 1.000 0.456* Sig. (2-tailed) 1.000 1.000. 0.029 N 27 27 27 23 RF Pearson Correlation 0.919** -0.456* 0.456* 1.000 Sig. (2-tailed) 0.000 0.029 0.029. N 23 23 23 23 (** : p<0.01, * : p<0.05) 192
Table XI. The mean & standard deviation of resonance frequency according to abutment length at bovine bone specimen. (unit : Hz) Abutment Length Direction Mean±S.D. Mean V 8506.00±210.79 3mm 8514.57 H 8523.13±140.13 V 8397.03±246.93 4mm 8397.37 H 8361.70±247.88 V 8000.47±226.14 5mm 7913.67 H 7826.87±396.89 V 7053.97±496.60 6mm 7082.17 H 7110.37±344.01 V 7073.17±314.78 7mm 6812.62 H 6552.07±284.21 V 6631.33±268.47 8mm 6354.92 H 6078.50±236.32 Table XII. The mean & standard deviation of Periotest according to abutment length & measuring direction at bovine bone specimen. Abutment Length Direction Mean±S.D. Mean V -4.47±0.51 3mm -5.18 H -5.90±0.48 V -3.13±0.68 4mm -3.95 H -4.77±0.43 V -1.33±0.48 5mm -2.20 H -3.07±0.58 V 0.47±0.57 6mm -0.48 H -1.43±0.50 V 3.30±0.70 7mm 2.65 H 2.00±0.59 V 5.33±0.61 8mm 4.50 H 3.67±0.48 Table XIII. The result of one-way ANOVA test of resonance frequency and Periotest according to abutment length, stiffness of specimen (bovine bone). Sum of Squares df Mean Square F Sig. RFA Between 2.35E+08 5 47178006 415.972 0.000* Groups Within 4.01E+08 354 113416 Goups Total 2.76E08 359 PTV Between 4.27E+03 5 854 876.346 0.000* Groups Within 3.45E+02 354 0.975 Groups Total 4.62E+03 359 (p<0.05) 193
V: Transducer installed perpendicular to the bone H: Transducer installed parallel to the bone Fig. 37. The value of resonance frequency value according to abutment length and measuring direction with 1mm transducer thickness(bovine bone). V: Transducer installed perpendicular to the bone H: Transducer installed parallel to the bone Fig. 38. The value of Periotest according to abutment length and measuring direction with 1mm transducer thickness(bovine bone). Table XIV. The mean & standard deviation of resonance frequency according to time at rabbit tibiae. (unit : Hz) Period Mean N Std. Deviation 0 Weeks 5885 96 488 4 Weeks 6316 96 458 8 Weeks 6434 96 360 12 Weeks 6642 96 378 16 Weeks 6982 96 446 Total 6451 480 561 Table XV. The result of one-way ANOVA test of resonance frequency value of implants inserted into rabbit tibia according to the time elapse. Sum of Mean df Squares Square F Sig. Between Groups 18138732.43 15 1209248.829 4.240 0.000 Within Groups 132322085.9 464 285176.9093 Total 150460818.3 479 (p<0.05) Table XVI. The result of Scheffea test of resonance frequency value of implants inserted into rabbit tibia according to the time elapse. Period N Subset for alpha =.05 1 2 3 4 0 Week 96 5884.9792 4 Weeks 96 6315.9583 8 Weeks 96 6434.1771 12 Weeks 96 6642.0313 16 Weeks 96 6981.5104 Sig. 1.000 0.457 1.000 1.000 (p<0.05) 194
가진되며, 물체를통과하여다른위치에서변위나속도가속도로서감지된다. 이때경로에따라전달되는비율이바뀐다. 그리고그전달률은주파수에따라서도바뀐다. 그러므로한점에서다른한점으로의전달되는전달률 H는주파수에대한함수이다. Fig. 39. The change of resonance frequency value of implants inserted into rabbit tibia according to the time elapse. H=H(f) 그리고이상적인물리계에서는전달율 H는입력과출력사이에서선형적인관계를갖는다. 따라서입력 X(f), 출력 Y(f) 과전달율 H(f) 과의관계를수식으로표현하면다음과같다. Y(f)=H(f) X(f) 치에대한정확도에영향을미치는요소를차단하였다 (Fig. 40). 위의수식을 block diagram으로표시하면 Fig. 41과같이표현된다. Ⅳ. 총괄및고안 질량과탄성을갖는모든물체는진동할수있다. 따라서대부분의기계나구조물은정도의차이는있지만진동하게된다. 특히기계나구조물의고유진동수가외부가진주파수와일치하면과도한변형이나파손을일으키는공진현상이발생하기도한다. 예전에는자연현상의이해측면에서물리계의진동을기술하기위한수학적이론을개발하여왔으나요즘에는많은연구들이기계, 기초, 구조물, 엔진, 터빈및제어계의설계와같은진동의공학적응용에역점을두고있다. 17-20,52) 일반적으로진동은자유진동과강제진동으로구분한다. 자유진동은외력이없는경우에계의자체에내재하는힘에의해발생한다. 자유진동인경우계는하나또는그이상의고유진동수를가지고진동하며이고유진동수는질량과강성의분포에의해서결정되는동적계의고유한특성이다. 이러한계에외부에서고유진동수와같은주파수로가진이되면진폭이매우커져서위험상태에도달하게된다. 교량, 빌딩또는비행기의날개와같은구조물의파괴는공진에의한경우가상당히많다. 따라서고유진동수의해석은진동연구에서매우중요하다. 20) 물체의한지점에서일정한진폭의정현파힘으로 Fig. 41. Transfer function in frequency region. 이러한주파수영역의전달계를시간영역에서해석하면, 이상적인물리계에서일정위치에외력 x(t) 를가하고특정위치의응답y(t) 를측정하면외력과응답의관계는 Fig. 42. Transfer function in time region. 여기서 h(t) 는시스템의입력과출력사이의시간영역에서의전달함수로서 x(t) 와 y(t) 의관계식은다음과같다. 이수식은주파수영역에서의전달함수를시간영역으로변환시킨결과이다. 즉시간영역에서 convolution은주파수영역에서곱으로바뀌는성질에의하여단순화된다. 본논문에서는전달함수 H(f) 또는 h(t) 가전달경로의환경에따라결정되는성질을이용하여응답 Y(f) 또는 y(t) 의특성을파악하여진동환경의변화 195
Fig. 43. Degree of freedom(d.o.f.) system. 를추적하고자한다. 17-20,52) 많은진동문제는매우복잡하지만공학적측면에서는복잡한해석과정을보다단순화하여해석을용이하게하면서도실제계의중요한특성을대변할수있는모형화기술이응용된다. 따라서진동이론에서는단순계의거동에대한해석에역점을두게되며이는단순계가실제로많다기보다는실제계를잘반영하기때문이다. 진동계를가장이해하기쉬운계는 1자유도계 (Degree of freedom (D.O.F.) system) 이다. 자유도란대상계의거동을완전히표현하기위해필요한최소한의독립적좌표계총수를의미한다. 1자유도계진동계는 Fig. 43과같이질량, 스프링, 감쇠요소로구성된다. 운동하는질량요소는정지중이거나운동중일때현재상태를계속유지하려는관성을가지며, 스프링요소는힘이가해질경우변형되며공급된일을위치에너지로저장하며, 감쇠요소는공급된에너지의일부를운동에의하여소산시키는역할을한다. 공진과공명의의미가혼용되고있는데공진은진동이특정주파수에대하여 standing wave를유발시켜외부가진력을계속누적시킴으로써진동반응을매우크게나타내는현상이고, 공명은공진에서진동이음향으로바뀐경우를의미한다 ( 초음파는공명에해당 ). 52) 임플랜트의생존과성공의개념은매우다르다. 생존은일반적으로환자의악골안에서임플랜트의유지에관계되고골질의안정성, 하중지지능력등은임상보고에서자주거론되지않는다. Albrektsson과 Sennerby 8) 은정밀하게임플랜트의성공과생존에대한개념을언급했고, 최근에 Roos 등 23) 은다른임플랜트시스템에서의여러가지임상보고를발표보고한바있다. 전체적으로골내임플랜트를더욱더명확히구분지을수있는성공의평가기준을가능토록하기위한정량적인측정기술 (quantitative technique) 이분명히필요하다. 주위골에알맞은임플랜트의안정성은식립후발생되는방해받지않는치유와골형성을가능케하는데필수적이며, 임플랜트와조직계면에서발생되는저작과기능시하중응력을적당히분산시켜주기도한다. 치유와기능을요구하는안정성은더욱다르며, 임플랜트식립에서의초기안정성과기능시의 2차적안정성을고려해야한다. 안정성은국소적골질, 골양, 임플랜트의기하학, 식립기술 ( 고정체의사용등 ), 길이, 직경및형태에관련된다. 5,6) 만일임플랜트가식립되는곳에서불충분한안정성을갖는다면미세동요가발생된것이다. 28,29,30) 미세동요는임플랜트의식립후즉각적으로뒤따르는것일수있으며, 이런경우정상적인치유과정은파괴된것이고, 임플랜트와조직계면에서골의개조와재생이발생되기보다는섬유성결합조직이채워지게된다. 이것은임플랜트의동요를유발시키고실패를가져온다. Brunski 등 30) 은사냥개의하악골에임플랜트를식립한뒤즉각적인교합력은미세동요에의해자극된비미네랄화된결합조직캡슐을형성한다고보고한바있다. 임플랜트의안정성과골유착에대한측정을위해서는가역적인임상적실험방법 (Non-invasive clinical test methods) 들을이용하는데다음과같은방법들이있다. 첫번째로타진반응을보면, 초기에임플랜트의골유착은금속성기구로지대치와임플랜트를타진해서평가할수있다고생각했었다. 그러나귀는음질의감폭혹은증폭된공명주파수를감지하는데불충분하고임플랜트와지대치를타진하는것은근본적으로복잡한계통을단순화해야하는문제점이있다. Wheel Tap Test 21) ( 전통적으로금이간기차바퀴를검사하는방법 ) 는구면실험이고한점에 tap 을가하여전체요소를조사한다. 정상적인것과손상된것을자연적주파수감폭에의해찾아내게된다. 두번째방사선검사는임상적기술중가장널리 196
사용되어진것이며임플랜트식립의술전평가와골유착, 지대치의안착을평가하는데도사용된다. 방사선촬영의목적은임플랜트주의의방사선투과상을찾기위함이며임플랜트주위골의높이를평가하는데사용된다. 가장일반적인것은임플랜트의내부치수가기준으로사용된다. Strid 24) 는임플랜트가치주점막으로덮혀치유과정에있거나후에지대치와연결되었을때 1년평균 0.1mm의골높이소실이발생한다고보고하였고, Roos 등 23) 은계속되는주변골소실은 IMZ 임플랜트에서 1년평균 0.5mm 이상으로발생됨을보고하였다. 이러한보조적인수단을이용한측정결과는신뢰성이떨어지는것으로사료된다. 세번째 Periotest (Siemens AG, Benshein, Germany) 는치아주위치주인대의감폭성향을양적으로측정하고, 그것의동요도를수치로나타내게설계되어개발되어졌다 14,15). 치주인대의 damping 효과를기본원리로하고 contact time을정량적으로측정하여치아동요도를나타내기위해고안된전자기구로임플랜트안정성연구에도많이이용된다. Periotest 는전자석을이용해치아쪽으로진척되는 metal slug가내장된 handpiece로구성되어있고, tapping head가치아에접촉하는시간을 accelerometer로측정한다. 기구에있는 software는접촉시간을치아동요의기능과연관시키도록고안되어있다. 성공적인임플랜트는 -5에서 +5의 PTV 범위를갖는다고보고하였고 14,15), Chavez와 Lance 31) 는56개의성공한나사형임플랜트에서동요도측정결과 -6에서 +2의범위를가지며평균 -3.07을나타낸다고하였다. Van Steenberghe 등 32) 은 321 개의임플랜트를 2 차수술후측정시 -6에서 +5의범위와평균 -2.39 ±2.15의 PTV를보고하였다. 이것은임플랜트가식립된위치, 골질, 길이에의해영향을받는다고보고하였다. Carr 등 33) 은 Periotest 와뒤틀림제거력측정에대해연구하여서로비례관계가있음을보고하였고, 조와임 2) 은 Periotest 를이용한상, 하악각부위의골질평가에관해연구하였다. 본실험의생체외실험에서 PTV 측정결과는지대주의길이차이에따라지대주의길이가 3mm일때 -5.18에서지대주의길이가 10mm일때 4.50의범위를나타내었다. 본연구의생체외실험에서동일길이의임플랜트 를 Hot Melt 에포매하여지대주의길이차이에따른공진주파수를측정한결과 3mm의지대주에서는 5953Hz(n=9, P<0.01), 10mm의지대주에서는 4968Hz(n=9, P<0.01) 의측정치를보였다. 이실험을통해공진주파수측정장치의측정치에대한신뢰성과반복적인재현성을얻었다. 또한유한요소법을통한예비실험결과를확인하기위해에폭시레진에노출길이를다르게임플랜트를식립하고, 지대주의길이차이를다르게준조건하에서공진주파수측정시. 트랜스듀서의두께가 0.5mm인경우공진주파수영역이 5,000Hz 미만에분포하였다 (n=9, P<0.01). 트랜스듀서의두께가 1mm 인경우공진주파수영역이 5,000 Hz에서 10,000Hz 사이에분포하였고 (n=9, P<0.01), 트랜스듀서의두께가 2mm인경우공진주파수영역이 10,000Hz 를초과해서분포하였다 (n=9, P<0.01). 유한요소법을이용한예비실험결과와유사한결과를보였고, 추가적인생체외실험과동물실험에서는두께 1mm의트랜스듀서를사용하였다. 임플랜트가식립된물성체의경도차이와지대주의길이차이에따른비교실험에서는물성체의경도가증가하고지대주의길이가감소함에따라공진주파수가증가되었다 (n=10, P<0.05). 따라서골질의강도는임플랜트의노출길이와지대주의길이와함께공진주파수에영향을미친다고사료된다. Meredith 32) 는임상에서공진주파수를이용한임플랜트안정성분석을하였는데, 임플랜트식립시모든임플랜트의평균공진주파수는 7437± 127Hz(n=56, P<0.05) 이고, 8개월후지대주연결시는 7915±112Hz(n=54, P<0.05) 로공진주파수는평균 427±88Hz(n=54, P<0.05) 증가하였고그차이범위는 -602에서 1047Hz의범위를나타냈다고보고하였다. 본실험에서는 16마리의가토경골에식립직후공진주파수측정결과 5889± 488Hz(n=96, P<0.05) 의측정치를나타냈고, 16주에공진주파수측정결과 6982±446Hz(n=96, P<0.05) 를나타냈다. 시간의경과에따른공진주파수는평균 1097±112Hz(n=96, P<0.05) 의증가를보였다. 본연구에서채택한공진주파수측정방법은트랜스듀서를임플랜트지대주혹은고정체에직접연결하는것으로 Meredith의정현파를이용한공진주파 197
수측정장치와비교시트랜스듀서의연결방법에있어서는유사하지만, 가진방식에있어임펄스방식을채택하였다. 트랜스듀서-지대주-임플랜트시스템은완벽하게재현가능하고반복될수있는요소라는것이핵심사항이며이것은측정과분석을간단하게하기위해매개변수를간단하게만들어야한다. 변환기의디자인은 cabling이편리하고임플랜트와지대주에작은나사를이용해고정되도록고안되었으며, 캔티레버빔을감작시키기위해서는 piezo ceramic element의사용이필수적이었다. 그러나 piezo ceramic element는고저항장치이므로노이즈나발생된공진주파수에예민하다. 14) 따라서트랜스듀서를임플랜트에결합시발생되는응력이잔류되어측정치에영향을미칠수있음을실험을통해입증하였고, 이러한응력의제거여부를측정할수있는프로그램을개발, 장착하여측정치가균일한반복성을가지도록하였다. 공진주파수에대한트랜스듀서의조임토오크의영향은초기단계에서검사되었으며, 변환기가 10Ncm 이상의토오크로조여있다면공진주파수의변화가없음을관찰할수있었다. 유한요소법을이용한가상실험결과와생체외실험을통해얻은결과를바탕으로트랜스듀서의두께를 1 mm로선택하여유효지대주길이, 임플랜트의노출길이혹은임플랜트가식립된골질에따라가장안정된공진주파수영역을확보할수있었다. 또한임펄스가진방식을채택하여정현파의가장큰단점인외부노이즈와전원노이즈로인한측정치의불안정성을해소한것은적절하고성공적이었다고사료된다. 본실험을통한공진주파수측정장치의개발은임플랜트의안정성과골유착측정을정량적으로표준화시키고측정데이터의신뢰성을보완한시도였다. 향후임상에서쉽고편리하게사용할수있으며, 이용효율을향상시키기위해개인용컴퓨터와증폭기를합쳐서소형화시키는것이개발여지로남아있다. 또한지속적인임상실험을거쳐임플랜트안정성에대한표준화된정량분석을시행하고, 이를통해임상에서얻어진공진주파수측정치가임플랜트의성공여부를절대적으로평가할수있고, 향후새로운형태의임플랜트개발에기본적인검증장치가되도록지속적이고집중적인연구가진행되어야할것으로사료된다. Ⅴ. 결론임플랜트의안정성은식립후발생되는방해받지않는치유와골형성을가능케하는데필수적이며, 임플랜트와조직계면에서발생되는저작과기능시하중응력을적당히분산시켜주기도한다. 치유와기능을요구하는안정성은더욱다르며, 임플랜트식립에서의초기안정성과기능시의이차적안정성을고려해야한다. 생체내에서임플랜트의안정성을정량적으로측정하기위한가역적인실험방법을개발하기위해본연구에서는물성체의고유진동수를측정하기위한공진주파수측정장치를개발하였다. 개발된공진주파수분석장치의자체안정성을검증하기위해생체외실험에서는인체의골경도와유사한물성치를가지는에폭시레진과신선한우늑골시편에임플랜트를식립하여공진주파수측정후데이타를분석하고, 측정치의검증을위해 Periotest 를이용한측정치와비교분석하였으며, 생체내실험에서는뉴질랜드산가토 16마리의경골에임플랜트를식립하여 16주까지 4주간격으로 5회공진주파수를측정하여다음과같은결론을얻었다. 1. Hot Melt에식립한동일한길이의임플랜트에서는공진주파수측정시균일한측정치를보였고, 지대주의길이가증가함에따라유의성있는감소를보였으며 (p<0.01), 트랜스듀서의두께가 0.5, 1.0, 2.0mm로증가됨에따라공진주파수는유의성있게증가되었다 (p<0.01). 2. PL-2와에폭시레진에노출량을다르게식립한임플랜트의공진주파수측정시노출량이감소되고지대주길이가감소될수록공진주파수가유의성있게증가되었다 (p<0.01). 3. 재료의물성차이에따른비교에서트랜스듀서의두께가증가할수록공진주파수가유의성있게증가하였고 (p<0.01), 임플랜트가식립된재료의강도가증가하고지대주의길이가감소할수록공진주파수는유의성있게증가하였다 (p<0.05). 4. 골시편에서공진주파수와 Periotest 측정시지대주의길이가증가함에따라두가지측정치모두에서유의성있는차이를보였고, 각각의측정방향에따른비교에서는유의성있는차이를보이지않았다. 198
5. 가토의생체실험에서는동일한길이의임플랜트에대하여공진주파수는일정한양상을보였으며 4주에서 8주간을제외한시간의경과에따라공진주파수가유의성있게증가되었다 (p<0.05). 이상에서공진주파수측정장치의개발은임플랜트의안정성과골유착측정을정량적으로표준화시키고측정데이터의신뢰성을보완한시도이며, 향후임상에서의안정된이용효율향상과임플랜트안정성의표준화된정량분석을위한연구가진행되어야할것으로사료된다. 참고문헌 1. Bra nemark PI. Osseointegration and its experimental background. J Prosthet Dent 1983;50:399. 2. Bra nemark PI. A biomechanical study of osseointegration. Ph.D thesis. Department of Orthopaedics, Institute of Surgical Science and Institute of Anatomy and Cell Biology, University of Gothenburg, Gothenburg, 1996. 3. Bra nemark PI, Hansson BO. Osseointegrated implants in the treatment of the edentulous jaw. Distributed by the Almquist and Wiksell periodical Co. 4. Bra nemark PI, Zarb GA, Albrektsson T. Tissue integrated prosthesis : Osseointegration in clinical dentistry, Chicago, Quintenssence Co, 1985;117. 5. Albrektsson T. Bone tissue response. In Osseointegration in clinical dentistry. Quintessence Co. Chicago 1985;129. 6. Albrektsson T, Bra nemark PI, Hansson HA, Lindstrom J. Osseointegrated titanium implants. Acta Orthop Scand 1981;52:155. 7. Albrektsson T, Jacobsson M. Bonemetal interface in osseoi- ntegration. J Prosthet Dent 1987;57:597. 8. Albrektsson T, Sennerby L. State of the art in oral implants. J Clin Periodontol 1991; 18:474. 9. Albrektsson T, Zarb GA, Worthington P, Eriksson AR. The long term efficacy of currently used dental implants : A review and proposed criteria of success. Int J Oral Maxillofac Implants 1986;1:11. 10. Meredith N. On the clinical measurement of implant stability and osseointegration. Ph.D. Thesis, Department of Biomaterials / Handicap Research, Institude for Surgical Sciences, Gothenburg University, Gothenburg, Sweden. 1997. 11. Meredith N, Alleyne D, Cawley P. Quantitative determination of the stability of the implant-tissue interface using resonance frequecny analysis : Clin Oral Impl Res 1996;7:261. 12. Meredith N, Book K, Friberg B, Jemt T, Sennerby L. Resonance frequency measurements of implant stability in vivo. Clin Oral Implant Research 1997;226. 13. Meredith N, Rasmussen L, Sennerby L, Alleyne D. Mapping implant stability by resonance frequency analysis. Med Sci. Research 1996;24:191. 14. Shulte W. The Periotest periodeontal status. Zahnarztl Mitt. 1986;76:1. 15. Shulte W. A new field of application of the Periotest mathod. The occlusal-periodontal load can now be measured quantitatively. Zahnarztl Mitt. 1988;78:474. 16. Derhami K, Wolfaardt JF, Dent M, Faulkner G, Grace M. Assessment of the periotest device in base line mobility measurements of craniofacial implants. Int J oral Maxillofac Implants 1995;10:221. 17. Theories Practices of Vibration Samsung Institute of Technology of Electon particle.1991;1. 18. Measurement of Vibration & Frequency 30 analysis International Industiral Information system. 1989. 19. Bruel and Kjaer : Model Analysis 1992 199
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U. Identification of bone quality in conjunction with insertion of titanium implants. Clinical Oral Implant Research 1995(a);13 :213. 40. Friberg B, Sennerby L, Roos J, Strid CG, Lekholm U. Evaluation of bone density using cutting resistance measurements and microradiography : an in vitro study in pig ribs. Clin Oral Impl Res 1995(b);6:164. 41. Elias JJ, Brunski JB, Scarton HA. A dynamic modal testing technique for non-invasive assessment of bone-dental implant interface. Int J Oral Maxillofac Implants 1996;11:728. 42. Chavez H, Lance FO. Assessment of oral implant mobility. J Prosthet Dent 1994;70 :421. 43. Lim JH, Cho IH : A study on the evaluation of Bone quality of Maxillo and Mandibule by using peroitest. 1994; 32:7,520. 44. Deutch JE, Brunski JB. Numerical analysis of load distribution among dental implants. AADR Meeting, San Francisco, Calif. 1989;Paper No. 587. 45. Hobo S, Ichida E, Garcia LT. Osseointegration and occlusal rehabilitation. Chicago, Quintessence Publ Co. 1989;265. 46. Lekholm U, Zarb GA. Patient selection and preparation. In Osseointegration in clinical dentistry (Branemark PI, Zarb G, Albrektsson T, eds). Quintessence Co. Chicago. 1985;199. 47. Sennerby L., Thomsen P, Ericson LE. Early tissue response to titanium implants inserted in rabbit cortical bone, Part 1 Light microscopic observations. J Mater Sci. : Mater in Med 1993;4:240. 48. Sennerby L, Thomsen P, Ericson LE. Early tissue response to titanium implants inserted in rabbit cortical bone, Part 2 Ultrastructural observations. J Mater Sci. : Mater in Med 1993;4:494. 49. Tsuboi Y, Sennerby L, Mori K, Matsuhisa H. The dynamic of the osseointegrated implant. Part 1: Theoretical analysis of the osseointegrated implant and the natural tooth by the vibration theory. Personal Communication. 1996. 51. Wennerberg A. On surface roughness and implant incorporation. Ph.D. Thesis. Department of Biomaterials/Handicap Research, Institute for Surgical Sciences, and Department of Prosthetic Dentistry, Gothenburg Universith, Gothenburg, Sweden. 1996. 52. Handbook of Noise & Vibration : The Korean Society for Noise & Vibration Engineers. 1995;221. Reprint request to: In-Ho Cho, D.D.S., M.S.D., Ph.D. Department of Prosthodontics, College of Dentistry, Dankook University 7-1, Shinpoo-Dong, Chunan, Chungnam, 330-716, Korea navydent@kangnung.ac.kr 201
사진부도 1 Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 8 Fig. 9 Fig. 10 Fig. 1. Bone specimen for experiment. Fig. 2. Abutment for experiment. Fig. 3. Periotest. Fig. 4. Transducer. Fig. 5. Piezo ceramic element. Fig. 6. Power & Charge Amplifier. Fig. 8. Finite element model (transducer thickness : 0.5 mm). Fig. 9. Stress distribution due to impulse (transducer thickness : 0.5 mm). Fig. 10. Finite element model (transducer thickness : 1 mm). 202
사진부도 2 Fig. 11 Fig. 12 Fig. 13 Fig. 16 Fig. 17 Fig. 18 Fig. 19 Fig. 20 Fig. 21 Fig. 11. Stress distribution due to impulse(transducer thickness : 1 mm). Fig. 12. Finite element model (transducer thickness : 2 mm). Fig. 13. Stress distribution due to impulse(transducer thickness : 2 mm). Fig. 16. View of sine sweep. Fig. 17. View of white noise. Fig. 18. View of impulse (impact). Fig. 19. Metal mold for fabricating of specimen. Fig. 20. Specimen of Hot Melt Adhesive. Fig. 21. Specimen of PL-2 Photoelastic Resin. 203
사진부도 3 Fig. 22 Fig. 23 Fig. 24 Fig. 25 Fig. 26 Fig. 27 Fig. 28 Fig. 40 Fig. 22. Specimen of PL-2 Photoelastic Resin. Fig. 23. Specimen of Epoxy Resin JRA-323. Fig. 24. Specimen of Epoxy Resin JRA-323. Fig. 25. Measuring of resonance frequency at bone specimen. Fig. 26. Measuring of Periotest value(ptv) at bone specimen. Fig. 27. Implantation on rabbit tibia. Fig. 28. Measuring of resonance frequency at rabbit tibia. Fig. 40. Monitor view of resonance frequency. 204
ABSTRACT A STUDY ON THE MEASUREMENT OF THE IMPLANT STABILITY USING RESONANCE FREQUENCY ANALYSIS Cheol Park, D.D.S., M.S.D., Ju-Hwan Lim, D.D.S., M.S.D., Ph.D. In-Ho Cho, D.D.S., M.S.D., Ph.D., Heon-Song Lim, D.D.S., M.S.D., Ph.D. Department of Prosthodontics College of Dentistry, Dankook University Statement of problem : Successful osseointegration of endosseous threaded implants is dependent on many factors. These may include the surface characteristics and gross geometry of implants, the quality and quantity of bone where implants are placed, and the magnitude and direction of stress in functional occlusion. Therefore clinical quantitative measurement of primary stability at placement and functional state of implant may play a role in prediction of possible clinical symptoms and the renovation of implant geometry, types and surface characteristic according to each patients conditions. Ultimately, it may increase success rate of implants. Purpose : Many available non-invasive techniques used for the clinical measurement of implant stability and osseointegration include percussion, radiography, the Periotest, Dental Fine Tester and so on. There is, however, relatively little research undertaken to standardize quantitative measurement of stability of implant and osseointegration due to the various clinical applications performed by each individual operator. Therefore, in order to develop non-invasive experimental method to measure stability of implant quantitatively, the resonance frequency analyzer to measure the natural frequency of specific substance was developed in the procedure of this study. Material & method : To test the stability of the resonance frequency analyzer developed in this study, following methods and materials were used: 1) In-vitro study: the implant was placed in both epoxy resin of which physical properties are similar to the bone stiffness of human and fresh cow rib bone specimen. Then the resonance frequency values of them were measured and analyzed. In an attempt to test the reliability of the data gathered with the resonance frequency analyzer, comparative analysis with the data from the Periotest was conducted. 2) In-vivo study: the implants were inserted into the tibiae of 10 New Zealand rabbits and the resonance frequency value of them with connected abutments at healing time are measured immediately after insertion and gauged every 4 weeks for 16 weeks. Results : Results from these studies were such as follows: The same length implants placed in Hot Melt showed the repetitive resonance frequency values. As the length of abutment increased, the resonance frequency value changed significantly (p<0.01). 205
As the thickness of transducer increased in order of 0.5, 1.0 and 2.0 mm, the resonance frequency value significantly increased (p<0.05). The implants placed in PL-2 and epoxy resin with different exposure degree resulted in the increase of resonance frequency value as the exposure degree of implants and the length of abutment decreased. In comparative experiment based on physical properties, as the thickness of transducer increased, the resonance frequency value increased significantly(p<0.01). As the stiffness of substances where implants were placed increased, and the effective length of implants decreased, the resonance frequencies value increased significantly (p<0.05). In the experiment with cow rib bone specimen, the increase of the length of abutment resulted in significant difference between the results from resonance frequency analyzer and the Periotest. There was no difference with significant meaning in the comparison based on the direction of measurement between the resonance frequency value and the Periotest value (p<0.05). In-vivo experiment resulted in repetitive patternes of resonance frequency. As the time elapsed, the resonance frequency value increased significantly with the exception of 4th and 8th week (p<0.05). Conclusion : The development of resonance frequency analyzer is an attempt to standardize the quantitative measurement of stability of implant and osseointegration and compensate for the reliability of data from other non-invasive measuring devices. It is considered that further research is needed to improve the efficiency of clinical application of resonance frequency analyzer. In addition, further investigation is warranted on the standardized quantitative analysis of the stability of implant. Key words : Non-invasive, Resonance frequency, Resonance frequency Analyzer 206