The use of dental implants has increased together with increases in the human life span and it has become an imperative subject for dentists to familiarize themselves with this treatment modality. Unfortunately, there has been no practical and quantitative method for in vivo evaluation of the stability of dental implants. In the tooth mobility examination, the tactile sense of natural teeth is different from that of dental implants. The authors have developed an automatic diagnosis system of tooth mobility for clinical use. The biomechanical mobility of peri-implantium is measured with a pseudo-random vibration, from which the viscoelasticity c1, c2, k of peri-implantium is obtained. The diagnosis system has been applied to the quantitative evaluation of the stability of implants : endodontics endosseous implants (titanium pin), endosseous implants (Bioceram). It has also been applied to the evaluation of the long-term prognoses of dental implantation (Bioceram) and the examination of Intramobile implant (IMZ), and the satisfactory results have been obtained

Kawazoe, Takayoshi

Oka, Hisao

Saratani, Keiji

Tanaka, Masahiro

Yamamoto, Tatsuma

Okayama University Digital Information Repository

Tooth Mobility Measurement of Dental Implants

Okayama University Scientific Achievement Repository

Memoirs of the Faculty of Engineering.Okayama University.Vo1.27.No. 2. pp.n-17. March 1993Tooth Mobility Measurement of Dental ImplantsHisao OKA-, Tatsuma YAMAMOTO-KelJI SARATANI--, Masahlro TANAKA-- and Takayoshl KAWAZOE"(Received January 29 . 1993)SYNOPSISThe use of dental implants has increased together With increases in thehuman l1fe span and it has become an imperative subject for dentists tofamiliarize themselves with this treatment modality. Unfortunately,there has been no practical and quantitative method for in vivoevaluation of the stability of dental implants. In the tooth mob1l1tyexamination, the tactIle sense of natural teeth is dillerent from that ofdental implants. The authors have developed an automatic diagnosissystem of tooth mobility for clinical use. The blomechanical mobility ofperi-implantium Is measured with a pseudo-random vibration. fromwhich the viscoelasticity CI, C2. k of peri-implantium Is obtained. Thediagnosis system has been applied to the quantitative evaluation of thestability of implants: endodontics endosseous implants (titanium pin).endosseous implants (Bioceram). It has also been applied to the evaluationof the long-term prognoses of dental implantation (Bloceram) and theexamination of Intramobile implant (lMZl. and the satisfactory resultshave been obtained.L INTRODUCTIONWhen we lose a function and form of a part of lMng body due to injury or disease, we make upfor the local defect in function and form by two methods: (1) transplantology using lMng tissues- Department of Electrical & Electronic Engineering,-- The Second Department of Prosthetic Dentistry, Osaka Dental University1112 Hisao OKA, Tatsuma YAMAMOTO, Keiji SARATANI, Masahiro TANAKA and Takayoshi KAWAZOEand organs (2) implantology using arUficial materials such as plastics, metals and ceramtes [l).As we enter the aging society, the public has high expectations for dental implants which can takethe place of and function just like natural teeth. In order to evaluate a dental implantation, theobservations of support system of implants placed in expertmental animals are madephysiologically and anatomically through a scanning electron microscope [2). Although thematerials and configurations of the implants are important, a biomechanical research of theimplants ts also indtspensable [3). An acoustic tapping method (10 to 150 kHz) was proposed forassessing the inter-facial rigidity of various bone implants [4). There has also been much workusing the finite element method (FEM) [5) on the stress analysts of the tissues surrounding theimplant. However. there has not yet been any reports of diagnostic methods for the clinicalevaluation of dental implants. The evaluation of the implant whether it has succeeded or failedhas been a subjective one by each dentist. A practical, cllnical method for the evaluation of dentalimplants ts needed.Although the mobility test by palpation is the Simplest and most basic cllntcal method, it isd1ffi.cult to evaluate the implant with the same tactile sense used to examine natural tooth.Siemens of Germany now markets a simple instrument, the Periotest, for the objectivemeasurement of periodontal function (6). Thts system has several weak points in diagnosingtooth mobility (7). In particular, the impact force may damage the implant, the surroundingtissue or the prosthetic restoration on the implant. Because the evaluation of mobility of healthyor pertodontally involved natural teeth has been subjective, we developed a diagnosis system forteeth mobility [7.8). and have applied it cltnteally (9). We have also applied this apparatus to theevaluation of different implants and new implant materials.2. MEASUREMENT OF BIOMECHANICAL PROPERTIESThe most common and simplest testing of biomechanical properties would be a manual toothmobility examination with an instrument or forefinger. The mobility is grouped into 4 degrees(MO-M3). A periodontium diagnosed as MO is clinically firm. healthy and within normalphysiological mobility. The higher number indicates both buccolingual and apical movement[l0). The classification by the manual examination involves a subjective estimation based onexperiences. The shock-absorbing system of natural teeth depends on gingiva and periodontalmembrane surrounding the teeth. The manual examination of natural teeth is consideredprtmarily to estimate a viSCoelasticity of periodontium including the periodontal membrane.The periodontal membrane of natural teeth, which is 0.1-0.3 mm in width. ts fibrous connectivetissue composed primarily of collagen fibers. perfused by a rich network of peripheral bloodvessels. The primary function of the periodontal membrane ts support of the tooth in the alveolarbone (II). Together with the gingiva, it moderates the impact force on the teeth. Thebiomechanical charactertstics of the implant, which must support the forces of occlusion andmastication, is extremely important in planning the prosthetic restoration. including theimplant itself. On the other hand, a load-displacement characteristic of the dental implantplaced in alveolar bone depends on a viscoelasticity of peri-implantium. When there is no softtiSsue and is a direct structural and functional connection between the surface of implant bodyand the alveolar bone, which ts considered to have a pure elasticity, the load and displacement ofTooth Mobitity Measurement oj Dentat Imptants 13the implant is in proportion to each other. When not a proportional but a creep characteristic canbe observed in a recovery response after a sudden removal of load. it is assumed that there is softtissue surrounding the implant body but no direct connection. Thus. it is difficult to evaluate theimplant, which does not have such a periodontium as a periodontal membrane of natural teeth.with the same tactile sense used to examine natural tooth.The authors proposed an automatic diagnosis system of tooth mobillty in order to measure abiomechanical properties of periodontium of natural teeth (7). Applying a small randomvibration onto labial crown of a tooth. a mechanical mobility (a reciprocal of mechanicalimpedance) is obtained and then viscoelasticity of periodontium are calculated. The diagnosissystem is detailed as follows : The tooth is randomly vibrated with 30 - 1000 Hz. The accelerationand force of vibrating point are detected and a fast Fourier transform (FIT) processing isperfOImed for both signals. The spectrum of mechanical mobility (an integral of acceleration Iforce) is obtained. Noyes and Solt proposed a biomechanical model [121 (two masses mi. m2. twodashpots Cl. C2 and a spring k) of the periodontal tissues shown in Fig. I. The five parameters arecalculated from the measured spectrum by a curve-fitting method. As CI. C2 and k correspond wellwith viscoelasticity of the periodontal membrane. which dominates the tooth mobility. theseparameters are chosen and expressed as a new mobility triangle figure (MT figure). The MT figureprovides a visual interpretation of the mechanical parameters. The centroid of the equilateraltriangles is 0 and each vertex represents the normalized mean for the parameters in the healthyperiodontium of the tooth. As periodontal disease advances. the MT figure shrinks and theparameters decrease accordingly. CI.C2 and k of healthy periodontium (MO) of maxillary centralincisor are 26.1 [Ns/ml. 310 [Ns/m) and 16.1 [x104 NIml. respectively. The reproducibility of thesystem is 6.89 % in coefficient of variation (standard deviation I mean value).-Fig. I. Biomechanical model proposed by Noyes and Solt [121.3. BIOMECHANICAL PROPERTIES OF THE PERI-IMPLANTIUMWith this diagnosis system. the surface of the prosthetic restoration placed on the implant issubjected to random mechanical vibrations in the faCio-lingual direction. and the mechanicalmobility spectrum is computed from the force and acceleration of the vibrating point. Thebiomechanical properties of the peri-implantium are then evaluated using viscoelasticparameters (7).3.1 Endodontics Endosseous ImplantsFig.2 shows the postoperative radiograph of a titanium pin endodontics endosseous implant ina maxillary right central incisor. The solid line in Fig.3 shows the mechanical mobility spectrum14 lIisao OKA. Tatsuma YAMA~IOTO. Keiji SARATA I. Masahiro TANAKA and Takayoshi KAWAZOE100frequency, Hz.1m1000Fig.2. Postoperative radiograph of atitanium endodontics endosseousImplant for a maxillary right centralIncisor.Fig.3. Mechanical mobility spectra of theendodontics endosseous Implant for theright central incisor (solid line). for thethe healthy left central incisor (brokenline), and after curve fitting using ablomechanlcal model (dotted line).of this Implant 22 days after placement where a bone defect had been restored by hydroxyapatite.The broken line In the figure Is the healthy left central incisor In the same patient. It can be seenthat slml1ar spectra were obtained for the endodontics endosseous Implant and the natural tooth.The dotted line Is the spectrum of the endodontics endosseous Implant follOwing the curve-fittingmethod using the blomechanlcal model. The viscosity constants CI and C2 were 24.3 and 487,respectively, and the elasticity k was 152. The objective tooth mobl1lty (7) was diagnosed as Ml.In contrast. the same three constants for a healthy incisor would be 38.9. 550. and 32.6,respectively.Flg.4 shows pre- (a) and postoperative (b) radiographs of endodontics endosseous Implants Infour maxillary incisors. There was resorption of the roots, reduction of the height of the alveolarbone. and resulting loss of periodontal support In the second premolars and the six anterior teethIn the maxilla. Clinical mobl1lty of the central incisors was diagnosed as M3. Flg.5 shows themechanical mobility spectra of the right (solid line) and left (dotted line) central Incisors afterImplantation. It Is clear that the right central incisor had recovered to an objective toothmobility of M1 and the left to MO. by means of the endodontics endosseous implantation.(a) preoparatlve radiograph (b) postoperative radiographFIg.4. Preoperative (a) and postoperatlve(b) radiographs of endodontics endosseousImplants In the four maxillary Incisors.3.2 End088eoUS ImplantsAs with endodontics endosseous Implants. the mobility of endosseous Implants Is differentfrom that of natural teeth which are supported by a periodontal membrane. This difference Is forthe most part determined by the composition and physical properties of the pseudo-periodontalligament at the Interface of the alveolar bone and the Implant. Although It Is different for eachTooth Mobitity .\teasllrem!!nt of Dental Implants 15endosseous implant. and comparison of individual cases may be dlflkult. qualitative evaluationof the pert-implantium seems possible. It can be conjectured that in cases where the v1scosity isvery small. the pert-implantium has a purely elastic character. and has at least partialosseointegratlon (3). Fig.6 shows the radiograph of a screw endosseous implant (Bioceram. 4AOL)for a maxillary left canine in a case where both the central and lateral incisors and the leftcanine were missing. The solid line in Fig.7 shows the mechanical mobility spectrum for thisimplant and the broken line shows the corresponding values for the natural tooth on the oppositeside. The dotted line represents the mechanical mobility charactertstics of the endosseousimplant following the curve-fitting method using the biomechanical model.As was the case with the endodontics implant. mechanical mobility charactertstics similar tothose for natural teeth were obtained. The clinical mobility was MO and the constants Cl. C2 and kwere 35.9 and 608. 152. respectively. The corresponding values for natural canines are MI. 12.9.311. and 14.0. Since the elasticity k for the implant was very large. it was assumed that theimplant had a pert-implantium. Fig.8 shows the so-called mobility trtangle (MT) for a screwendosseous implant (Bioceram. 3AOL) for a maxillary rtght lateral incisor. The implant had beensplinted to the adjacent central incisor with ceramometal crowns placed with temporary cement.The solid lines in the MT figure are from the first measurement which was obtained 9 monthsafter implantation. The dot-dashed lines represent the second measurement. which was1000100'1~•.001 L---'---'-....l..l.....10.zEi'Ol~tEFIg.5. Mechanical mobility spectra forendodontics endosseous implants in theright central (solid line) and left central(dotted line) incisor.FIg.6. Postoperative radiograph of aBioceram implant for a left canine.frequency. Hzk.~\/1. .,~/' '\? \\I /. ,\I .: \\I I: ,\r ' I \\,,~ ! )...... '~\,,' .J.:::... ........ \ '\IJ, '" --"'-.. \ '\£ .:..&---_'r_':'_=_:.:..~_~.C 1 C 2FIg.S. Mobility trtangle (MT) for ascrew endosseous implant for amaxillary rtght lateral incisor. Thesolid lines were obtained 9 monthsafter implantation. the dot-dashedlines 7 days later. and the dotted lines96 days after that.1000100.1__.001 L-......I.......I...LL.L...I..LU._..L-I....L..l....I.I.JUl10.zE...01.l::EFIg.7. Mechanical mobility spectra for ascrew endosseous implant for maxillaryleft canine (solid line), the natural canineon the opposite side \broken line). and aftercurve fitting using a mechanical model(dotted line).16 Hisao OKA, Tatsuma YAMAMOTO, Keiji SARATANI, Masahiro TANAKA and Takayoshi KAWAZOEmade one week after the first. The dotted lines show the values recorded 96 days after the secondmeasurement. The broken lines show the mean values for a natural tooth with healthyperiodontium. It can be seen that the condition of the peri-implantium recovered to that of ahealthy tooth in about one year. The postoperative course of this endosseous implant splintedwith a natural tooth has been successful. The MT was valuable asset in evaluating the progress ofthis endosseous implant.4. INTRAMOBILECYLINDER IMPLANTSThe intramobile cylinder (IMZ) implant, with its unique stress absorbing element (IME), wasdeSigned in 1970 and has been used in clinical practice since 1978 (l3). It is a stress breakingmechanism which acts as a shock absorber, distributing stresses in the endosseous implant (14).Thus it plays the role of the periodontal membrane for the endosseous implant which hasattained osseointegration. Fig.9 is the graphical representation of an IMZ implant which hasbeen placed in plaster. Fig. 10 shows the MT figure when polyoxymethylene resin IME (solid line)and titanium (dotted line) were used as the insert. The broken lines show the mean values for atooth with healthy periodontium. Although the values of the parameters with the resin wereslightly greater than those of a natural tooth, the elasticity for the titanium was about doublethat of the natural tooth. These results indicate that the IMZ functions as a stress breaker tohorizontal loads and is effective as a buffer for the osseOintegration of endosseous implants.However, tests should be carried out in the future on this system using actual clinical cases sincethe results from implants in plaster are not sufficient.rt:;:;:::r--"~---crownintramobileelementb..,..,...,.+-- implant bodyimproved stoneFIg.9. Intramobile cylinder (IMZ)implant embedded in model plaster.5. CONCLUSIONSFIg.lO. MT for the polyoxymethyleneresin IME (solid line) and titanium element(dotted line).The tactile sense dUring palpation for mobility in natural teeth is different from that in dentalimplants. The automatic diagnosis system for tooth mobility discussed here is very effective inthe quantitative evaluation not only of the condition of an implant but also in the evaluation ofchanges which occur in implants over long periods of time.REFERENCESTooth Mobility Measurement of Dental Implants 17(I]H. Kawahara: Oral Implantology and Biomaterials. Elsevier(1989). p.5.(2]D.E. Steflik. R V. McKinney. D.L. Koth : Oral Implantology and Biomaterials [Histological andultrastructual observations of the tissue responses to endosteal dental implants),Elsevier(1989). pp.75-81.(3]J.B. Brunski : Int. J. Oral Maxillofac. Implants. 3(1988). p.85.(4rr. Kaneko: J. Materials Science. 22(1987). pp.3495-3502.[5]M. Ogino. M. Fujino : Oral Implantology and Biomaterials (Dental Root Implant Coated withBioactive Glass). Elsevier(1989).pp.139-144.(6]B. d'Hoedt. D. Lukas. L. Mfihlbradt. W. Schulte. F. Quante. A. Topkaya : Dtsch zahn<'l.rztl.. z-40(1985). pp.1I3-125.[7]H. Oka. T. Yamamoto. K. Saratani. T. Kawazoe : Med. BioI. Eng. & Comput.• 27(1989). pp.75-81.[8]H. Oka. T. Yamamoto. K. Saratani. T. Kawazoe : Medical Progress through Technology.•16(1990). pp.1I7-124.[9]K. Saratani. S. Yoshida. H. Oka. T. Kawazoe : Oral Implantology and Biomaterials (The clinicalmeasurement of the biomechanical mobllity of dental implants). Elsevier(1989). pp.305-31O.[lO]C.L. Halstead. G.G. Blozis. A.J. Drinnan. RE. Gier : Physical evaluation of the dental patient.C.V. Mosby Co.(1982). p.318.[lI]B.K.B. Berkovitz. B.J. Moxham. H.N. Newman: The periodontal Ligament in Health &Disease, Pergamon Press(l982). p.276.(I2]D.H. Noyes. C.W. Solt : J. Biomechanics. 6(1973). pp.439-442.(I3IA. Kirsch, P.J. Mentag : J. Oral Implantology. 12(1986). pp.576-588.[14]E.J. Richter. B. Orschall. SA Jovanovic: J. Biomechanics. 23(1990). pp.297-306.

Tooth Mobility Measurement of Dental Implants

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