2 2 20 0 00 0 07 7 7년 년 년 8 8 8월 월 월 석 석 석사 사 사학 학 학위 위 위논 논 논문 문 문
다 다 다양 양 양한 한 한 두 두 두께 께 께로 로 로 T T Ti i iN N N 코 코 코팅 팅 팅된 된 된 지 지 지대 대 대주 주 주 나 나 나사 사 사의 의 의 반 반 반복 복 복 착 착 착탈 탈 탈 후 후 후
풀 풀 풀림 림 림력 력 력에 에 에 관 관 관한 한 한 연 연 연구 구 구
조 조 조 선 선 선 대 대 대 학 학 학 교 교 교 대 대 대 학 학 학 원 원 원
치 치
치 의 의 의 학 학 학 과 과 과
김 김
김 한 한 한 수 수 수
다 다 다양 양 양한 한 한 두 두 두께 께 께로 로 로 T T Ti i iN N N 코 코 코팅 팅 팅된 된 된 지 지 지대 대 대주 주 주 나 나 나사 사 사의 의 의 반 반 반복 복 복 착 착 착탈 탈 탈 후 후 후
풀 풀 풀림 림 림력 력 력에 에 에 관 관 관한 한 한 연 연 연구 구 구
2 2
20 0 00 0 07 7 7년 년 년 8 8 8월 월 월 2 2 24 4 4일 일 일
조 조 조선 선 선대 대 대학 학 학교 교 교 대 대 대학 학 학원 원 원
치 치
치 의 의 의 학 학 학 과 과 과
김 김
김 한 한 한 수 수 수
다 다 다양 양 양한 한 한 두 두 두께 께 께로 로 로 T T Ti i iN N N 코 코 코팅 팅 팅된 된 된 지 지 지대 대 대주 주 주 나 나 나사 사 사의 의 의 반 반 반복 복 복 착 착 착탈 탈 탈 후 후 후
풀 풀 풀림 림 림력 력 력에 에 에 관 관 관한 한 한 연 연 연구 구 구
지 지 지도 도 도 교 교 교수 수 수 정 정 정 재 재 재 헌 헌 헌
이 이 이 논 논 논문 문 문을 을 을 치 치 치의 의 의학 학 학 석 석 석사 사 사학 학 학위 위 위 논 논 논문 문 문으 으 으로 로 로 제 제 제출 출 출함 함 함. . .
2 2
20 0 00 0 07 7 7년 년 년 4 4 4월 월 월 1 1 18 8 8일 일 일
조 조 조선 선 선대 대 대학 학 학교 교 교 대 대 대학 학 학원 원 원
치 치
치 의 의 의 학 학 학 과 과 과
김 김
김 한 한 한 수 수 수
김 김
김한 한 한수 수 수의 의 의 석 석 석사 사 사학 학 학위 위 위 논 논 논문 문 문을 을 을 인 인 인준 준 준함 함 함. . .
위
위 위원 원 원장 장 장 조 조 조선 선 선대 대 대학 학 학교 교 교 교 교 교 수 수 수 계 계 계기 기 기성 성 성 인 인 인 위
위 위 원 원 원 조 조 조선 선 선대 대 대학 학 학교 교 교 교 교 교 수 수 수 김 김 김학 학 학균 균 균 인 인 인 위
위 위 원 원 원 조 조 조선 선 선대 대 대학 학 학교 교 교 교 교 교 수 수 수 정 정 정재 재 재헌 헌 헌 인 인 인
2 2 20 0 00 0 07 7 7년 년 년 5 5 5월 월 월 일 일 일
조 조 조 선 선 선 대 대 대 학 학 학 교 교 교 대 대 대 학 학 학 원 원 원
C C
Co o on n nt t te e en n nt t ts s s
국 국
국문문문초초초록록록ㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ ㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ ⅣⅣⅣ I
I
I...IIINNNTTTRRROOODDDUUUCCCTTTIIIOOONNNㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ 111 I
I
IIII...MMMAAATTTEEERRRIIIAAALLLSSS AAANNNDDD MMMEEETTTHHHOOODDDSSSㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ 444 I
I
IIIIIII...RRREEESSSUUULLLTTTSSSㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ 888 I
I
IVVV...DDDIIISSSCCCUUUSSSSSSIIIOOONNNㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ 111333 V
V
V...CCCOOONNNCCCLLLUUUSSSIIIOOONNNㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ111999 R
R
REEEFFFEEERRREEENNNCCCEEEㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ 222111
L L
Li i is s st t to o of f fT T Ta a ab b bl l le e e
Table1.Classificationofgroupsㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ 4 Table2.Themeanabutmentscrew weightㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ11 Table3.Themeandetorqueforceofeachgroupㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ12
L
L Li i is s st t to o of f fF F Fi i ig g gu u ur r re e es s s
Fig.1.Abutmentscrewsusedinthisstudyㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ5 Fig.2.Fixtureandabutmentconnectionㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ5 Fig.3.Specimen-holdingapparatusformeasurementofdetorqueforce
ㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ7 Fig.4.Digitaltorquegaugeandmeasurementofdetorqueforceㆍ ㆍ ㆍ 7 Fig.5.FE-SEM micrographsshowingcoatingsurfaceofeachgroup
beforerepeatedclosingandopeningㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ8 Fig.6.FE-SEM micrographsshowingcoatingsurfaceofeachgroup
afterrepeatedclosingandopeningㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍㆍ10 Fig.7.Comparisonwithmeandetorqueforceofeachgroupㆍㆍㆍㆍㆍ 12
국
국 국문 문 문초 초 초록 록 록
다다다양양양한한한 두두두께께께로로로 TTTiiiNNN 코코코팅팅팅된된된 지지지대대대주주주 나나나사사사의의의 반반반복복복 착착착탈탈탈 후후후 풀
풀
풀림림림력력력에에에 관관관한한한 연연연구구구
김한수
지도교수 :정재헌,치의학 박사 조선대학교 대학원,치의학과
TiN 코팅은 가장 일반적이고 대중화된 코팅 방법으로 황금과 같은 색깔을 띠므로 심미적으로 우수하며 금속표면에 코팅 시,마찰계수의 감소와 부식에 대한 저항,기계적 취약함의 해소 등이 보고되었으며,산업적으로도 널리 사 용되고 있다.치과계에서도 기구의 수명연장을 위해 TiN 코팅이 사용되어 지 고 있으며,최근 TiN 코팅을 지대주 나사에 적용시키려는 시도들이 이루어지 고 있고 TiN 코팅된 지대주 나사에서 마모와 적합도,풀림력이 향상되었다는 결과들이 보고되고 있다.그러나 임플란트 지대주 나사에 TiN을 코팅 시 정 량화된 코팅 두께에 대한 연구는 보고되지 않고 있는 실정이다.이에 본 연 구에서는 타이타늄 지대주 나사에 TiN 코팅 시간을 달리해 다양한 두께로 TiN을 코팅 처리 한 후,반복 착탈 시 이들의 표면 변화와 풀림력을 조사하 여 TiN 코팅을 지대주 나사에 적용함에 있어 최상의 풀림력과 물리적 성질 을 제공하는 코팅의 두께를 결정하여 임상적으로 문제가 되고 있는 지대주 나사의 풀림현상을 해소하는데 그 목적이 있다.
35개의 코팅되지 않은 타이타늄 지대주 나사가 본 실험에서 사용되었으며 TiN 코팅시간을 달리한 6개의 실험군(30분,60분,90분,120분,150분,180분) 과 TiN 코팅 처리를 하지 않은 1개의 대조군으로 10회의 반복 착탈 시 표면 변화와 풀림력을 평가하여 다음과 같은 결과를 얻었다.
1.코팅되지 않은 지대주 나사에 비해 코팅된 지대주 나사는 비교적 균질하고 매끈한 표면을 보였다.
2.코팅하지 않은 지대주 나사와 30분간 코팅된 지대주 나사에 비해 60분 이상 코팅된 지대주 나사에서 반복 착탈 후의 표면 변화가 없었다.
3.코팅하지 않은 지대주 나사와 30분간 코팅된 지대주 나사에 비해 60분 이상 코팅된 지대주 나사에서 반복 착탈 전과 후의 무게의 변화가 적었다.
4.코팅하지 않은 지대주 나사에 비해 코팅된 지대주 나사의 평균 풀림력이 높은 값을 나타내었다.코팅된 지대주 나사들 중에서 60분간 코팅된 지대주 나사가 평균 풀림력이 가장 높게 나타났으며 평균 풀림력의 감소 경향도 가장 적었다.
결론적으로,균질하고 매끈한 표면 및 반복 착탈 시에 마모 저항성과 풀림 력을 증가시키기 위해서는 적절한 TiN의 코팅 두께가 요구되며.이 실험의 결과를 토대로 지대주 나사의 우수한 기계적 성질을 얻기 위해서는 약 60분 이상의 TiN 코팅이 요구된다고 할 수 있다.
In recentyears,theuseofosseointegratedimplantshasbeen popularin single tooth restoration,and partially edentulous and fully edentulous restoration.Regardlessofthetypeofperformedrestoration,inmostcases, ascrew connection isused between theabutmentand implant.However, implantabutmentscrew loosening hasremained a problem in restorative practices1,2).Abutmentscrew loosening was reported in large numberof studiesandrangedfrom 2% to45% oftheabutment3-6).Screw loosening isarecognizedcomplicationinimplantrestorations7-11).
Themaintenanceofascrew jointisachieved when theclamping force exerted by the screw exceeds the jointseparating forces acting on the assembly12).To reduce the possibility ofscrew loosening,potentialjoint separating forces should be minimized by optimal positioning and angulation ofthe implants.Jointseparating forces may exceed clamping forceswhen implantassembliesaresubjectto non-axialloading because ofimplantpositionorangulation,orexcessiveocclusalforces13).Cantilever designs may amplify forces on screw joints due to thelevereffectand should,whenpossible,beavoided14).
Preload is the term given to the tension generated in the screw upon tightening andisadirectdeterminantofclampingforce.Astheabutment screw istorqueddown,preloadisgeneratedwithinthescrew,placingthe abutment/implantassembly undercompression15,16).This is a function of the frictional forces in the mating threads and screw head, the metallurgicalproperties ofthe screw,and the applied closing torque16). Micromovement, component surface wear, and embedment relaxation during functionalloading may gradually erode the preload and cause progressiveslippageandscrew jointfailure16,17).
Whentorqueisappliedtonew screws,energyisexpendedinsmoothing
surface.After thread engagement,surface asperities are flattened and additionalinput torque is applied toward elongation of the screw and generationofpreload.Itisclaimedthatthreadfrictionishigheroninitial closure,decreasing afterrepeated tightening and loosening cycles16).The process ofscrew loosening underclinicalconditions,whethergradualor sudden,hasto overcomethetension in thetightened screw and friction betweenthematingcomponents.
When torqueisapplied toanew screw,about90% ofinputtorqueis used to overcome friction and only 10% to induce preload18).For that reason,afew manufactureshadalteredthesurfaceofabutmentscrew to reduce the friction coefficient and obtain the higher preload19,20).The well-known abutmentscrews are Gold-Titeof3i(3i® ImplantInovations, INC.,U.S.A.)and TorqTiteofSteri-Oss(NobelBiocareAB,Sweden)and WCC ofOsstem(Osstem.Co.,Ltd.,Korea).
Martin etalreportedthatGold-TiteandTorqTiteabutmentscrewswith enhanced surfaces helped reduce the friction coefficient,and generated greater rotationalangles and preload values than conventionalscrew2). DragoreportedthattheuseofGold-Titesquareabutmentscrews,torqued to 32Ncm,maintained a stable abutment/implant connection that was successfulinclinicalpracticeforoneyear21).
Titanium nitride(TiN)coating is the mostgeneraland popularcoating method and used to improve the properties of metallic surface for industrialpurposes.This coating layer of2-3μm thickness renders the surface scratch-proofand is considered to be clinically stable22).TiN is used as a hard coating formetalcutting tools likedrills and burs,and formingtoolssuchasdiesandpunchesbecauseithashighhardness,low frictioncoefficientandgoodresistancetoadhesivewear22).Additionally,it hasagoldenappearanceandisusefulforornamentalpurposes.
TiN coating hasbeenappliedtoclinicaldentistry sinceearly times.The
clinicaltrials which coated crown,partialfixed denture and removable prosthesesmadefrom casting dentalalloy with TiN had been performed by severaldentists22).Kim etalreported thatTiN coating ofabutment screw helped to reduce the risk ofscrew loosening and improved the stability of screw joint23).When TiN coating applied to the abutment screw,frictionalresistancewould be decreased,asa results,thegreater preload and prevention of the screw loosening could be expected.
However,theproperthicknessofTiN coatingonabutmentscrew hasnot beenreportedyet.
Thepurposeofthisstudywastoevaluatetheremovaltorquevalueand surface change of titanium abutment screw with various TiN coating thickness.
Thirty five non-coated GSII abutment screws(GSASR,Osstem.Co.,Ltd., Korea)wereprepared forTiN coating.Theywererandomlyselectedand divied into 7 groups. According to coating deposition time(CDT), experimentalgroups were divided into 6 groups:group A(CDT 30min), groupB(CDT 60min),groupC(CDT 90min),groupD(CDT 120min),group E(CDT 150min), group F(CDT 180min). TiN was coated for the specimensof6 groupsrespectively,and thoseof1 group(group G)was notcoated asa controlgroup.Each group wasmadeup of5 abutment screws(Fig.1,Table1).
Table1.Classificationofgroups
Group Specimen No. Coating deposition time Applied torque
A 5 30 min 30Ncm
B 5 60 min 30Ncm
C 5 90 min 30Ncm
D 5 120 min 30Ncm
E 5 150 min 30Ncm
F 5 180 min 30Ncm
G* 5 None 30Ncm
* : Control group
1)TiN coatingusingArcionplating
TiN coatings were produced by Arc ion plating on titanium abutment screw.Forcontrolling ofcoating thickness,each group had thevariation ofcoating deposition time,such as30,60,90,120,150,and180minutes.
Temperaturewassupportedto350-380℃ onpurposetoincreaseadhesion degree.
2)Mountingofimplantfixtures
The implant fixtures used in this study were internal conical joint design(GSII, with diameter 4mm and length 13mm, Osstem.Co.,Ltd., Korea).AbutmentsforthisexperimentwereGS TransferAbutment(Hex Standard,with diameter 5mm and gingivalheight 3mm and abutment height 5.5mm, Osstem.Co.,Ltd., Korea). Thirty five pairs of implant fixturesand abutments wereselected respectively.Onefixture,abutment andabutmentscrew comprisedaspecimen.Each fixturewasmountedin liquid unsaturated polyester.Themounting media(Epovia,CrayValley Inc.
Korea) was a 2-part system made up resin and hardener. Two componentsweremixed togetherand cured overnightafterfixtureswere embedded.Aftermounting mediawascompletely hardened,abutmentwas connectedtoeachfixture(Fig.2).
Fig.1.Abutmentscrewsusedin Fig.2.Fixtureandabutmentconnection thisstudy(Osstem.Co.,Ltd.,Korea)
3)Ultrasonic cleansingofspecimens
Abutmentscrews were cleansed with alcoholand aceton in ultrasonic cleaner(Branson3510,Bransonic,USA)for10minutes.
4)FE-SEM and EDX investigation ofthread surface on the abutment screw
FE-SEM(Field Emission Scanning Electron Microscoper)was used to
observe change ofthread surface ofthe abutmentscrew afterrepeated closing andopening 10trials.Thethreadsurfaceofeachabutmentscrew was observed at100 magnifications,and then screw crest,valley,and slope were observed more detailed numerical value, at 1,000, 10,000, 100,000and500,000magnifications.
For examining the changes ofcoating surface,we operated qualitative analysis by EDX(Energy Dispersive X-ray Spectroscopy), when we carriedoutrepeatedopeningandclosingatbeforeandafter.
Care was taken notto touch the thread surface ofabutmentscrew for avoidanceofitscontamination.Theabutmentscrewswerealso cleansed withanultrasoniccleanerbeforetakingphotomicrographs.
5)Measurementofabutmentscrew weight
Forcomparison ofbonding strength andwearresistanceofvariousTiN coating thickness on abutment screw, before and after closing and opening,abutmentscrew weightwasmeasuredbyelectricscales(GENIUS ME,Sartorius,Germany)up to 0.000001g level.Identicalmeasurements wererepeatedlyperformed10timesforeachsample.
6)Measurementofdetorqueforce
Theimplantmounted fixtureblockswerefixed in thespecially devised specimen-holdingapparatusbeforeclosingandopening(Fig.3).
Each abutmentwas secured to the implantfixture by abutmentscrew with recommended torque value(30Ncm)using fingerscrew driver(Hand Driver, Osstem.Co.,Ltd., Korea) and torque wrench(TWMW, Osstem.Co.,Ltd.,Korea).Fingerscrew driverwasusedtofixtheabutment screw tillthread mating components were slightly contact.After that, torquewrench wasused totighten thescrew to30Ncm.Itwasused to insure that an accurate and reproducible force was applied to each abutment screw.The abutment screws were repeatedly tightened and removed 10 trials. The number of trials included several try-in of
abutmentscrew up to finalsetting.One operatorwho had experienced implantprosthetic restorations accomplished this operation.Sample with abutment screw tightened was fixed in the customized jig for the measurement of detorque force.Detorque forces were measured with digitaltorquegauge(MGT 12Ⓡ,Mark-10Corp.,U.S.A,Fig.4).
Fig.3.Specimen-holdingapparatus Fig.4.Digitaltorquegaugeand formeasurementofdetorqueforce measurementofdetorqueforce
SPSS statisticalsoftware forWindows(Release 12.0,SPSS Inc.,Chicago, IL,U.S.A.) was used for statisticalanalysis.One-way ANOVA(Tukey test;levelofsignificance,P<0.05),independentt-test(levelofsignificance, P<0.05),andvaliditytestofMicrosoftExcelwereusedforthecomparison ofthe mean detorque forces and the tendency ofdetorque force change measured from coating groups and uncoating group,between coating groups.
1)Beforerepeatedclosingandopening
As the resultofobserving coating surface with 100 magnifications and 500,000 magnifications, uncoated surfaces of control group(group G) showed somewhat rough surface, TiN particles adhered to coated experimentalgroup surfaces.And,themorecoating thicknesswasthick, the better size of adhered TiN particles were increased at same magnification(Fig.5).
In a resultofqualitative analysis ofcoating surface by using EDX,Ti, Al,and V were detected in uncoated controlgroup(group G),and those wereidentifiedby Ti-6Al-4V alloy.In experimentalgroup,Ti,Al,andV were detected,TiN was additionally detected.Also,the more coating thicknesswasthick,thebetterTiN particleamountswereincreased,and thelessTi,Al,andV detectedamountsweredecreased(Fig.5).
GroupA
GroupB
GroupC
GroupD
GroupE
GroupF
GroupG
Fig.5.FE-SEM micrographs& EDX showingcoatingsurfaceofeach groupbeforerepeatedclosingandopening
(Left:⨯100,Right:⨯500,000,Below:EDX)
2)Afterrepeatedclosingandopening
Comparing to before opening and closing,surface change on allgroups wasnotobservedinlow magnificationFE-SEM.Butinthehigh-powered FE-SEM analysis ofGroup A and Group G had noticeable changes in screw threads aftertest.The separation ofcoated TiN was detected in abutmentscrewsofGroupA,andGroupG wasrevealedthewearsurface andscratches.When observedby high-poweredFE-SEM,surfacechange in other groups was not represented before and after opening and closing(Fig.6).In result of qualitative analysis of coating surface by using EDX,surface ingredients did nothave difference as comparing to beforeopeningandclosing.
GroupA GroupB GroupC GroupD
GroupE GroupF GroupG
Fig.6.FE-SEM micrographs showing coating surface of each group afterrepeatedclosingandopening(⨯500,000)
Inresultofmeasuringweightofabutmentscrew beforeandafteropening andclosing,GroupG representedthemostremarkableweightchange,and Group A represented the most remarkable weight change among TiN
coatedgroups(Table.2).
Table.2.Themeanabutmentscrew weight (Unit:g) Before After Difference GroupA 0.125432±0.000019 0.125420±0.000012 0.000012±0.000016 GroupB 0.125940±0.000089 0.125920±0.000045 0.000020±0.000084 GroupC 0.125912±0.000013 0.125908±0.000016 0.000004±0.000006 GroupD 0.122552±0.000015 0.122540±0.000010 0.000012±0.000022 GroupE 0.125808±0.000011 0.125808±0.000009 0.000000±0.000010 GroupF 0.126018±0.000008 0.128010±0.000007 0.000008±0.000015 GroupG 0.125582±0.000008 0.125456±0.000011 0.000076±0.000011
Table 3.show the mean detorque forces ofeach trial.Group B had a highermeandetorqueforcethanothergroups.TiN coatinggroupsshowed higherdetorqueforcethangroupG.Allgroupshadaincreasing tendency ofdetorqueforceastheclosing andopening wererepeatedby3rdor4th trial.And,When werepeated thenumberoftrialsafter3rd or4th trial, detorqueforcesshoweddecreasedtendency.In3rdor4thtrial,allgroups hadmaximalmeandetorqueforce(Fig.7).
There was a statistically significantdifference between Group B and GroupG(P<0.05,independentt-test).In thecomparison ofmean detorque force from 1st trial to 10th trial, there was statistically significant difference Group B and Group G(P<0.05, One-way ANOVA). About maximalvalue,minimalvalue,andalltrialdetorqueforces,GroupB was higher than Group G.After 4th trial,two groups revealed declining tendency ofmean detorqueforces,and Group G wassteeperthan Group B onslopeofdeclining tendency.Incoating groups,suchasGroupA,B, C,D,E,andF,thougheveryabsolutemeandetorqueforcewasdifferent, thetendencyofdetorqueforcetransitionwasalmostsimilar.Therewasa statistically significantdifference between Group F and Group G(P<0.05,
independentt-test).Although maximaldetorque force ofGroup F was almostsametoGroupG,generaltendency ofdetorqueforcechangewas very different.Additionally,the mean detorque forces between Group F andGroupG exceptfor4thtrialrepresentedconsiderablelargedifference.
Table.3.Themeandetorqueforceofeachgroup (Unit:Ncm) Trial GroupA GroupB GroupCGroupD GroupE GroupFGroupG
1 26.26 27.06 26.6 25.92 25.32 24.84 24.1 2 26.46 27.46 26.8 26 25.58 25.04 24.3 3 26.66 28.08 27.16 26.22 25.78 25.26 25.02 4 26.52 28.4 27.22 26.16 25.7 25.3 25.24 5 26.42 28 26.9 25.82 25.38 25.02 24.54 6 26.16 27.74 26.66 25.66 25.24 24.66 24.36 7 25.88 27.34 26.48 25.5 25.04 24.46 23.88 8 25.58 27.18 26.3 25.24 24.82 24.16 23.36 9 25.44 26.98 26.06 25.14 24.62 23.92 22.84 10 25.2 26.9 25.88 24.94 24.44 23.66 22.48 Mean 26.06 27.51 26.61 25.66 25.19 24.63 24.01 SD ±0.51 ±0.52 ±0.44 ±0.44 ±0.45 ±0.57 ±0.89
20 21 22 23 24 25 26 27 28 29
1 2 3 4 5 6 7 8 9 10
Trial
Detorque force Group A
Group B Group C Group D Group E Group F Group G
Fig.7.Comparisonwithmeandetorqueforceofeachgroup
Theprevalentmethodtoreducethescrew loosening istheapplication of drylubricantcoating onabutmentscrew24).Thepurposeoflubricantisto reduce a frictionalcoefficientand obtain a higherpreload.The need for coatingwithlubricanthaslongsinceintroduced.
When titanium slidesin contactwith othermetalsofsimilarhardness, the friction coefficient is initially fairly low.However,the values of frictioncoefficientgradually increasetothatfortitanium againsttitanium, as tightening and loosening are repeatedly performed.Abkowitz et al found this increase in the frictionalcoefficientto be attributable to the galling and seizing tendency of titanium25).TiN film has low friction coefficient,high hardness and good wear resistance.Considering these properties ofTiN coating,itseems to be an alternative coating method according to result.Koo etaloperated TiN coating to abutmentscrews and examined thosesurfacecharacteristics.Asaresult,abutmentscrews revealed salient improvement of mechanical properties26). Also, Kim reported thattitanium abutmentscrew coated with TiN scored a higher meandetorquevaluethantitanium abutmentscrew27).
Researching aboutproper TiN coating thickness,Lee operated various thickness TiN coating to titanium alloy disk and examined on that mechanical property.In result of that study,he reported thatwhen CDT(coating deposition time) was 30min,coating thickness was 0.5㎛, CDT 60minwas1.05,CDT 90min was1.32,CDT 120min was1.40,CDT 150minwas1.72,CDT 180minwas2.10andcoatingthicknesswasthicker than 2㎛ forabutment screw had homogeneous and smooth coating surface and the high-quality mechanical property28). However, we considered that Lee's study had limitation of experiment as not mechanicalproperty ofabutmentscrew butthatofdisk.Therefore,the purpose ofthis study was to investigate the removaltorque value and
surface change of titanium abutment screw of various TiN coating thickness.
According to researchers including Mezger, TiN coating was good propertiesonwear-resistance,corrosion-resistance,andsurfacehardness22). But,researchersmentionedthatcoatingfilm hadneedofhomogeneityand consistency because defect of coating surface such as pores or micro-crackswereobserved.
When clamping torqueforcewasapplied tomicro-roughnessscrew,the points of loading application over yield strength generated and plastic deformationhappenedatthesepoints.
Settling effect,isthephenomenonthatearlycontactareaofsurfacewas deformed and flattened at the points of loading application over yield strength29).Plastic deformation happened untilcontactarea thatcan be stabilize screw,and ifthe whole settling effectwas largerthan elastic extension ofscrew,then loading appliedpointsofthreadscouldnotseize screw.Consequently,theloosening ofscrew occurred30).Sakaguchietal, they reported that2-10% preload disappearedby theinfluenceofsettling effect31).Binon etal,reported thatthe intensity ofsettling effectwas controled by early surface roughness, surface hardness, and applied force19).Thelessroughnessofcoatingsurfacewas,thelesssettlingeffect happened. Consistent and smooth coating surface was needed for decreasingofscrew looseningpossibility.
In this study,when we observed abutment screw surface,especially upper3-4screw threads,according toSopwithstudy thelengthofscrew only performed secondary roleforscrew fixation on technologicalaspect, andhesuggestedthatabout3-4screw threadswasenough tofix upper structuretight32).Intheresultofobservingabutmentscrew surfacebefore
openingandclosing,weobservedArcionplatingTiN film surfacebyuse of FE-SEM, Group G surfaces represented traces that happened on grinding process,other coated groups were observed relative consistent and smooth surfaces.And,the more coating thickness was thick,the bettersizeofadheredTiN particleswereincreasedatsamemagnification.
AstheresultofEDX ingredientsanalysis,TiN ingredientswereincreased bygetting along coating time.Thisfactrepresentedthatsurface-attached TiN ingredients were increased as coating time was increased.When analyzed ingredients by EDX,TiN proportion beyond certain thickness levelwas observed equally by depth limitation thatincidentbeam from FE-SEM couldcollide.
WhensurfaceofTiN coatedabutmentscrew wasobservedafteropening and closing,as the result,abutmentscrews coated with TiN over 60 minutesdid nothavesurfacechange,and theexfoliation ofTiN coating wasobservedatGroupA.Inprocessoftherepeatedopening andclosing ofabutmentscrew,forpreventing coating layerfrom exfoliating easily, adhesion strength should be high,and abutment screw needed to be coated for60minutes.Afteropening and closing,ThedifferenceofEDX value was notrevealed as comparing to before opening and closing.
Accordingtothisresult,itisconsideredthatrepeatedopeningandclosing didnotaffecttheingredientcompositionchangeofcoatingsurface.
Onthebasisofthisresult,whenabutmentscrew wascoatedwithTiN, ifyou wantabutmentscrew to be homogeneity and consistency and to minimize the plastic deformation of TiN coating surface at repeated openingandclosing,abutmentscrew neededtobecoatedwithTiN for60 minutes. And clinically, it is considered that further studies about quantitativenumericalvalueofproperadhesionstrengthwasneeded.
Ifcoated materials ofabutmentscrew had the low abrasion resistance, plastic deformation happened easily,and the abrasion or exfoliation of coating film was occurred.Also this resultcan cause screw tightening problem.Finally,coating materialofabutmentscrew had to begreatin abrasion resistance,thereforetheminimization ofscrew loosening can be accomplished.
Abrasion resistance was not directly measured on abutment screw becausesizeofscrew istoosmallandshapeiswinding.Thus,thisstudy evaluatedtheabrasion resistanceascomparing with changesofabutment screw weightatbeforeandafteropeningandclosing.
As shown in Table.2,the reduction of weight at before and after opening andclosing wasremarkableinGroupA andGroupG,therewas a statistically significantdifference between allgroups(P>0.05,One-way ANOVA). However, weight difference was very small. Therefore, abutment screw needed minimal coating time over 60 minutes for decreasingofabutmentscrew abrasionatrepeatedopeningandclosing.
In allgroups,detorque force value up to 3rd or 4th trialrepresented increasing tendency, and detorque force value represented declining tendency from 3rdor4th trialto10trial.Thereasonthatdetorqueforce represented these tendency was settling effect,mechanicalor adhesive wear.The reason of increasing tendency of detorque force was that irregularity between fixture surface and coating surface was gradually decreased by settling effect.From 3rd or4th trialto10trial,thereason ofdeclining tendencywasthatfrictionbetweenscrew surfaceandfixture surfacewasincreased,andthatdetorqueforcewasconsequentlydecreased because preload was decreased by adhesive or mechanicalwear33) In
analysisofthetendency ofdetorqueforcetransition,thepointwehaving in mindwasthatsettling effectandadhesivewearwerenotindependent phenomenons.Two effects simultaneously acted like two sides of the samecoin,butthesedetorqueforcetendency wasrevealed becauseeach effectdifferentlyaffectedtosurfacefrom rangetorange.Theinfluenceof settling effectwas more remarkable up to 3rd or4th trial,influence of adhesiveormechanicalwearwasmoreremarkablefrom 3rd or4th trial to 10 trial.Also,especially settling effectaffected to show the maximal detorqueforceat3rdor4thtrial.
There was a statistically significant difference between Group F and Group G(P<0.05,independentt-test).In every trial,detorque forces of GroupF werehigherthanGroupG detorqueforces,andalsointendency of detorque force change Group F was more gentle. This result representedthatTiN coatedabutmentscrew wasbetterthanraw titanium abutmentscrew oneveryaspect34).
Ascoating to abutmentscrew with TiN oflow friction coefficientand good hardness,itis considered thatdetorque force was increased and loosening of abutment screw was decreased.According to studies of researchers including Lee, those studies suggested that TiN coating thickness ofpropermechanicalproperties was over2㎛28).Butin actual fact,GroupB(1.05㎛)representedthehighestaveragedetorqueforcewhen researched detorque force on abutmentscrew at repeated opening and closing.
There were severalpotentiallimitations to this study.The specimens were randomly selected and tested by one researcher.The number of samplewasafew and thefrictioncoefficientcouldnotbefoundbecause sizeofscrew wastoosmallandshapewaswinding.
TiN coating had influence on detorque force,tightening-turning angle, and clamping force.However,This study didn't measure compression
forceandtightening-turningangle.Inthisstudy,weassumedthatsetting value of torque-generating device was always 30Ncm.But the force generated by torque-generating device might be not regular35). The possibilitygeneratingthiserrorwaspassedoveronprocessofthisstudy.
Therefore,these factors could make the errors of experimental data.
Finally,test was performed under only repeated closing and opening withoutocclusalloading.
In this study,fordetermining on properTiN coating thickness when TiN coating applied to abutmentscrew,weused implantsystem having internalconicaltypebetweenimplantandabutmentconnectionjoint.After various TiN thickness was coated to titanium abutmentscrew,surface change and detorque force of abutment screw was measured for evaluating proper coating thickness at repeated opening and closing.
Accordingtothisstudyresult,weobtainedthefollowingconclusions.
1.Themorecoating deposition timeincreased,themoresurfacebecame consistentandsmooth.
2. In abutment screw TiN coated over 60 minutes, surface change wasnotfoundedafterrepeatedopeningandclosing.
3.In abutmentscrew coated over60 minutes,little weightchange was foundedbetweenbeforeandafterrepeatedopeningandclosing.
4.TheTiN coatedabutmentscrew wasbetterthannon-coated abutment screw on the mean detorque value.In TiN coated groups,abutment screw mustbe coated during 60 minutes foraccomplishing maximal detorqueforceandgentledecliningtendencyofmeandetorqueforce.
Forobtainingconsistentandsmoothcoatingsurface,resistingabrasionat repeated opening and closing of screw,and increasing detorque force, coating layer of proper thickness was demanded. Conclusively, when titanium abutmentscrew was coated with TiN,thickness ofGroup B condition represented the distinguished improvement of mechanical property.This factis considered thatwe can improve screw loosening
problem asTiN coatingofimplantabutmentscrew.
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