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An intra-oral telemetry system for the continuous recording of vertical jaw movement
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1975 Phys. Med. Biol. 20 355 (http://iopscience.iop.org/0031-9155/20/3/001) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 130.102.42.98 This content was downloaded on 03/10/2015 at 10:44
Please note that terms and conditions apply.
PHYS.MED. BIOL.,
1975, VOL. 20,
NO.
3, 355-365. @ 1975
An Intra-oral Telemetry System for the Continuous Recording of Vertical Jaw Movement G. H. DIBDIX,? PH.D and M. J. GRIFFITHS, M.B., B.s., F.D.S, The M.R.C. Dental Unit? and The University of Bristol Dental School, Lower Maudlin Street, Bristol BS1 2LY, England Received 19 August 1974, inJinal f o r m 22 October 1974 Continuous measurement of the separation between upper and lower dental arches, the so-called interocclusal distance ( I O D ) , isof interest in dentistry. Criteria for making such measurements by radio telemetry are discussed. It is concluded that a transmitter small enoughto fit in a molar tooth gapis necessary in order to minimize interference withnormal function;other design factors are related toobtaining adequate frequency stability, on which measurement accuracy depends. A transmitter fulfilling these requirements is described which sensed the instantaneous value of IOD by the frequency change produced when a metallic object (dental filling, gold crown, shorted turn of wire or piece of ferrite) in one dental arch moved relative t o the transmitter in the other. Errors due to lateral and protrusive jaw movements were measured. Careful design and the use of high grade ceramic chip capacitors resulted in a transmitter of good frequency stability ( f 0.030/6 in 10 h, f 0 . 0 2 ~ o / o cand ) small size (10 x 7 x 5 mm). An example is given illustrating IOD movements due to swallowing, speech and respiration.
ABSTRACT.
1. Introduction
Cont'inuous measurementsof the separation bet'ween upper and lower dental arches, the so-called interocclusa,l distance or 'freeway space', are of interest in st'udying many problems in dentistry. Approaches to the problem of making such measurements have varied from the use of unwieldy mechanical devices (Garnick and Ramfjord 1962, Knap, Richardson and Bogstad 1970, Provost and Towle 1972), which musthave interfered greatly with function, to recent more sophisticated methods. These have included: opto-electronic (Geissler 1972, Duxbury and Rothwell 1973), and inductive devices (Laird, Manson,Davies and vonFraunhofer 1971), which nevertheless required rods or wires to project from betweenthe lips; and Fukushima, t'elemetry systems (Thomson and MacDonald 1969, Bando, Kawabata and Kohno 1972, Joniot 1974), which removed the necessityfor wires and, as long as the bulk was kept small, should have int'erferedless with normal function. This paper presents a discussion of some of the important factors governing measurement of interocclusal distance (IOD) by radio telemetry, together with a description of equipment which has been designed with these in mind. 2. Requirements 2.1. Range
The equipment was mainly intended for studies of the resting value of IOD, itsvariationwithtimeandtheeffecton it of changes inbodyposture, 13
356
G. H . Dibdin and
X .J.
Griflths
situations of stress, type of sleep and so on. For these a range of IOD measurement from 0 to 5 mm seemed adequate from preliminary studies; most speech patterns also appeared t o lie within this range, which was therefore taken as the minimum required. 2 . 2 . Accuracy
It is difficult to define the accuracy requirement; a mere indication of IOD wouldbeuseful, althoughreasonableprecision is clearlydesirable.Greater absolute accuracy is required at thelower values O f IOD to make their percentage error reasonably small. An uncertaint'y corresponding to i 5% of reading, or rf: 0.1 mm, whichever is greater, was t'herefore considered adequate. 2.3. Resolution It is desirable to have greaterresolution than implied by theabove accuracy figures, in ordert o make it possible to compare patternsof small IOD movements, as distinct from measuring absolute values. 2.4. Frequency response Under circumstances where, for example, the IOD goes to zero with a resultant sudden tooth contact, there is a rapid deceleration which, if it is to be reproduced faithfully, needs a frequency response up to perhaps 20 or 30 Hz. However, for adequate reproductionof the more gentle movements involved in studiesof the resting value of IOD, a response up to two hertz isgenerally quite adequate. 3. The choice of measuringsystem It is desirable that t'he measuring system should not affect the freedom of movement of the jaws in any way, which in case strain gauges or potentiometers, coupled to the upper and lower jaws simultaneously, are excluded because of the elastic and frictiona'l constraints they impose. There remains the possibility of mounting a transmitter in or on one dental or arch,itsoutput being modified according to separation,byinductive capacitative int'eraction with a component of the other dental arch. Because of the high dielectric constant of water and of soft tissue generally, a capacit'ative dist'ance transducer is subject to severe inaccuracies produced by humidity fluct'uat'ions and movement of the cheek and tongue. The remaining choice is between different types of inductive transducer. Of these, the balanced'variablepermeance'differentialtransformer (see for example in the case of IOD studies Parfitt 1961) is the most accurate and linear, but would require a core attached toone arch tomove wit'hin acoil att'ached to the other, inhibit'ingfreedom of lateral and protrusive movement of the jaw. It is advantageous for the information on IOD to be obtained in the form of a change of transmitt'er frequency,since calibration is then independentof signal strength. It is possible to do this without the limitation of a differential transformer, by making use of the frequency change produced when a magnetic or conductive material moves towards or away from the field of the transmittercoil. This was the system chosen for the present work, and briefly described elsewhere
Telemetry of Vertical Jaw Movement
357
(Griffiths and Dibdin 1973). The transmitter consisted of asmalloscillator (fig. 1) mounted on one dental arch with its coil lying in the occlusal plane, while a non-penetrating ‘core’ was attachedtotheotherarch.The ‘core’ consisted either of high permeability ferrite, increasing the inductance of the coil according to its proximity, or else an amalgam restoration, gold crown or shorted turnof wire, in which case the effective inductance was decreased. The circuit diagram of the transmitter is shown in fig. 2. The main design requirements were (1) minimalinterference withnormalfunction and (2) good
t”-l Receiver
Fig. 1. The telemetry transmitter (T) in a first molar tooth space of the lower jaw, its transmission frequency (f)being altered according to the proximity of the ‘core’ (C) consisting of ferrite, a metallic restoration or a shorted turnof wire. 2.2 -3.3K
Fig. 2. The transmitter circuit : a Hartley oscillator with centre-tapped coil.
frequency stability against all variables other than the one under study. The influence of these factors on the design (frequency of operation, method of construction and so on) are dealt with below. 4. Transmitter design factors
4.1. Interference with function In the absence of external wires, etc., the only factors associated with the transmitter which might interfere with function, and so modify the measurements themselves: are the transmitter bulk and weight. This becomes a more
358
G . H . Dibdin and M . J . Grifiths
important factor if, as in the present case, studies are not confined to denture wearers. It was considered desirable to limit the bulk of the transmitter to about that occupied by molar tooth, so-thatit would be possible to fit it in a good percentage of the commonly found gaps left by routine extraction of a permanent molar. Alternatively, the device had to be small enough to attach to the buccal (cheek) side of a permanent molar tooth, so that it projected as littleas possible. It was also considered desirable to limit the transmitter weight to less than that of an average molar tooth, to avoid influencing the dynamic balance of the jaw unduly. 4.2. Frequency stability
Because of the small frequency shift produced by the variable under study (about 10 kHz in 500 kHz, or 2y0)the frequency had tobe stabilized to within f 100 Hz ( k 0.02yo)for the period of unattended measurement, to reduce errors below f 1% of full scale deflection. This was enough to give the measurement accuracy discussed in section 2 . 2 , taking account of the nonlinearity of the system.The following arethemaindisturbing variables which hadto be considered. (a) Xoft tissue movement. Movement of cheek and tongue cause variation in the stray capacitance of the transmitter, shifting the transmission frequency. This can be minimized by making the tuning capacitance very large in comparison with anystraycapacitance, which in turn necessitatesarelatively low frequency of operation. These considerations led to a choice of transmitter frequency in the region of 500 kHz, with a tuning capacitance of 1500-2200 pF. Under these conditions effects due to soft tissue movement were found Do be negligible. (b) Moisture penetration. A transmitter contained within the mouth must be reasonably insensitiveto frequency drift or damage dueto moisture penetration. The large value of tuning capacitance already described in (a) is a help in this respect, but it is clearly desirable to encapsulate the whole transmitter in as impermeable a covering as possible. However, it is well known that all plastics slowly absorb moisture, the water uptake byepoxy resins being from 0.5 to 1yo by volume after prolonged exposure, and rathermore in the case of cold setting acrylics, Mackay (1970) has shown that moisture uptake for paraffin waxes is, in contrast, verysmall indeed, andsuggests that epoxy encapsulated telemetry transmitters be coated with wax before use to improve their water repellent properties. Early transmitters in the present work were totally encapsulated in aspecial electrical grade of epoxy resin (Araldite MY753 with HY951 hardener). More recently, however, the following procedure has been found simpler and, in view of Mackay’s work, preferable. The complete transmitter-battery system was encapsulated in capacitor grade insulation wax, and then coated with a thin layer of epoxy or cold setting acrylic for mechanical strength. The wires for an external on/off switch were brought to the surface as a bifilar spiral to extend the path length for any moisture tracking preferentially down the wires. This later design has the great advantage that the outer case can be cut away,
Telemetry of Vertical Jaw Movement
359
without damage to the circuitry, and a new battery inserted before re-coating it with plastic. Any voids or cracks in thewax were resealed after encapsulation by placing the area concerned close to the tipof a warm soldering iron. (c) Change in oral temperature. Oral temperature shows some variation due to mouth breathing, etc.,even in healthy subjects.It was found that the temperature of a transmitter in place in the mouth varied by as much as & 1 'c over the period of measurement, necessitating atemperature coefficient of frequency for the transmitter better than & 0.02y0 per degree C, in order to obtain the accuracy required. Until recently this was difficult to achieve in a small low frequency transmitter as required in (a), because of the difficulty of fitting a capacitance as large as 1500 pF andof the required temperature stability, into so small a space. However, with the adventof much smallerNPO grade ceramic chip capacitors it is now possible to obtain a packing density of about 300 p F per mm3 using these high stability components. Frequency stability obtained in the present design was usually in the range & 0 ~ 0 1 - 0 ~ 0 2per ~ 0 degree C, measured with the aid of a constant temperature water bath and a digital frequencymeter,although occasionally transmittershad coefficients which were lower. (d) Battery voltagelbattery age. To minimize slow drift during an experiment it is important that the variationof transmitter frequency with battery age is low. The circuit design chosen had the effect of limiting current drain to between 0.15 and 0.3 mA, given a possible battery life of between 70 and 140 h, using a fully charged RM212H Mallory cell, the smallest available. As can be seen from the battery discharge curves shown in fig. 3 this arrangement led to a greatly 1.4 \ 0.14 mA -
0.26 mA
'
;1.0 -
1.0 rnA
1
0 ~ 8 20~ " 40" " 60" " EO " " 100 ~
120
140
Time (h)
Fig. 3. Voltage-time discharge curves for the Mallory cell type RM212H showing the improved voltage plateau obtained at low discharge currents; this gives better transmitter frequency stability against time.
reduced rate of voltage drop comparedwith that obtained at the 1.5 mA discharge rate(battery life 8-12 h) used byotherauthors(Thomsonand MacDonald 1969, Joniot 1974). I n addition, theinclusion of the 2.2-3.3k collector series resistor shown in fig. 2 stabilized the working point, making the frequency itself less susceptible to battery voltage variation. I n a test on a transmitter completely immersed in normal saline a t 37 5 0.1 'c, the measured frequency drift due to both battery ageing and moisture uptake was less than k 0.03y0 in a 10 h period. Although
360
G. H . Dibdin and
AM.J . Grifiths
ideally this could be even lower, it was adequate to make overnight measurements a possibility without excessive baseline drift. (e) Sensitivity to lateral and protrusive jaw movements. Since it is desirable for the transmitter and 'core' to be as smallaspossible, protrusiveorlateral excursions of the jaw a t constant IOD are likely to cause some change in t'heir mutualinteraction,resultinginmeasurementerrors a t eachvalue of IOD. Fig. 4 shows the errors for a small transmit'ter,measured with a set-up designed
Lateral ( x ) andprotrusive
( y ) dlsplacement (mm)
Fig. 4 . Change in apparent interocclusaldist'ance (IOD) due t o lateral movements (a). and protrusive movements( y ) of the jaw a t three fixed values of true IOD.
t o allow lateral and protrusive movements x and y: a t constant values of IOD. It can be seen that the errors start to become serious a t excursions of more than 2-3 mm, depending upon separation. However, at IOD values less than 1 mm or so, where the percentage error is greatest. interlocking of the teeth tends to inhibit such movement'. Moreover: where the 'core, is in the form of a row of restorations or gold crowns, t'he error due to protrusive (and to a lesser extentlateral)movements can be furtherreducedbyasuitable choice of geometry, involving maximal extension of the coil perpendicular to the line of theserestorations(i.e.towards cheek andtongue):withoutthe device becoming noticeable to the wearer. Constructional details of transmitter Referring to thecircuit diagram infig. 2 the components used were as follows : Transistor: Microelectronics type MT4103 subminiature epoxy. Resist'ors : Ardentehearingaid type RSXOO. Capacit'ors: 1.5-2-2 n F : Vitramon type VJlPlOA XPO grade ceramic chip. 330 pF : Vitramon type VJ0808A NPO gradeceramicchip. Coil : 2 x 28 turns of 48 swg enamelled copper wire, wound as a bifilar coil on a 'i x 10 mm former, waxed and removed. All transmitter components except coils and bat'tery were cemented lightly together in a small rectangular pack 4 x 3 x 2 mm, and interconnections were made using a soldering iron with a 0.8 mm diameter bit. Four wires were left projecting from this pack for connection to the battery, which was positioned immediately a,longside,and t o the coil which was placed on top of t'he combined assembly. Connections to the batterywere made either with conducting paint 5.
Telemetry of Vertical Xovement Jaw
361
(Silver Dag, fromAcheson Colloid, Ltd.) or by means of small pressure contacts. Capacitor wax was melt'ed into the assembly, ta'king care not' t o overheat the of battery, after which it was dip-coated with acrylic or epoxy resin. A pair twisted wires mas brought to t'he surface for switching the power on and off. The met'hod of mounting t'he transmitter in a tooth gap with the required positional stability is shown in fig. 5 . A replica of the st'andard transmitter n
Transmitter
Undercuts
Fig. 5 . Method of mounting the transmitter in a tooth gap. The split retainer was placed in the tooth gap with t'he transmitterposit'ioned in the recess shown, holding the two halves of the split retainer apart so that they located in natural undercuts on t'he adjacent teeth.
shapewasfirstmadeinself-curingacrylicresin, then coatedwith silicone grease or ot'her release agent. X plaster cast of the subject's t'eeth was similarly coated around t'he tooth gap to be used, and into this was pressed the transmitter replica, surrounded by a part'ly cured doughy mass of a dental plastic (Trim, from H. J. Bosworth and Co., Chicago). When cured, this assembly was held firmly in position bJ- the naturally undercut contoursof neighbouring teeth. A vert'ical saw cut through the mid-line of the transmitter replica and the surrounding plastic enabled the assembly to be removed in two halves. Extraction of the replica pieces left a split retainer (fig. 5 ) accurately contoured to the teeth and the transmitter. The ret'ainer was placed inthe subject's toot'h gap, and the actual transmitter inserted. This gave good positional stabilit'y without undue pressure being exerted on the surrounding tissues. 6. Transducer calibration Calibration of the receiver output in terms of IOD was achieved by getting the subject to bite gently into different thicknesses of impression wax, and noting the corresponding output deflection.Measurement of t'heseparationcaused by these wax bites on t'he plaster models of the subject"s teeth then gave t'he IOD and receiver output'. Calibrationchecks requiredrelationshipbetween could be made during a' recording session by asking the subject to close his teeth together, and then to open his mouth as wide as possible. i . The receiver
A block diagram of t,he receiver is shown in fig. 6. The 500 kHz radio signa,l was picked up on a loop aerial worn around the subject,'s neck. This provided
G. H . Dibdin and N . J . Griflths
362
the input for a miniature battery-powered RF preamplifierbasedupon the Mullard 470 kHz I.F. module type LP 1166. The preamplifier was individually coils for 'open', tuned t o each telemetry transmitter by peaking the three tuning 500 kHz
Preampllfler (LP 1166)
1.
Mlxer/IF
10-20kHz
Arnpllfler/ l,miter
-1 1
Frequency divider
L
1-2 kHz Frequency meter
(+Io)
Stereo-cassette
Loudspeaker
+ I
Commentary
I
Chart recorder
Fig. 6. The receiver. The 500 kHz signal was converted t o an IF of 10-20 kHz, frequency divided and fed t'o the linear frequency meter. The 1-2 kHz signal could also be recorded onto stereo casset'te tape, together with a commentary, and replayed as indicated by the pecked lines for later chart recorder display.
'midway' and 'closed' values of IOD. To facilitatetuning,t'he preamplifier carried a miniature moving coil indicator which showed output signal level and also gave an indication of battery condition. The preamplifier output was fed via a lightyeight,low impedance coaxial lead to the main receiver (which could therefore be located some distance away), where it wasmixedwitht'he local oscillatorsignalin the mixer amplifier 6 signal (fig. 6) a t a n (MullardTAD 110). This gave a square wave output the intermediatefrequencyvarying from 10 t o 20 kHzdependingupon instantaneous value of the subject'sIOD. The following circuit (IC type FJJ141) divided t'he frequency by 10 t o give a 1-2 kHz square wave output suitable for recording on one channel of a stereo cassette tape recorder as described elsewhere (Dibdin 1974); a commentary was recorded on the ot'her channel. Finally, Ohis frequency modulated signal was replayed as indicated by t'he pecked lines in met'er (Anderson 1972) which gave an fig. 6, and used t'o drive a linear frequency output voltageproportional to frequency,forcalibrationinterms of the subject's IOD. 8.
Discussion
By following the design criteria which havebeen discussed, transmitters have been produced with the following specifications : 1Ox7x5mm Dimensions : including battery. 750 mg Weight - : 480-530 kHz. Frequency of operation : Frequency deviation : F 5 kHz (typical).
Telemetry of Vertical Jaw Movement Frequencystability
:
363
(a) withtemperature:betterthan i 0.02y0 per degree C . (b) with time: better than f 0.03y0 over a 10 h periodwhenimmersedinnormalsaline at 37
OC.
Battery current: 0.15-0.3 mA. Battery life : (R" 212H) 40 minimum. h Error in IOD measurement due to lateral and protrusive movement : approximately 7% a t IOD = 2 mm for excursions of k 2 mm, increasing for greater excursions. Frequency response : 0-30 Hz with oscilloscope output'. 0-2 Hz with pen recorder output'. Useful measurement' range : 0-6 mm approx. As would be expected from itsmode of operation, the response of the system is nonlinear. This can be seen from the sample trace given in fig. 7, which shows a drop in sensitivitya t larger values of IOD ; usually t'heuseful range of measurement was about 0-6 mm. Inaccuraciesdue to temperature fluctuations and
F"
Fig. 7. A sample of IOD data obtained using the t,elemetry system described. Examples of swallow (S), speech (Sp) and small rhythmic variations due t o respiration (R) can be seen. The parts marked C(C) and C ( 0 ) are calibration checks made during the course of a recording, when the subject was asked to close his teeth toget'her for a, few seconds, and then open as wide as possible.
drift were about k 0.05 mm or k 2.5% of reading (whichever was greater) up to anIOD of 3 mm, increasing to f 6% of reading a t a nIOD of 5 mm. IOD values greater than 12 mm or so caused no further deflection, giving an upper limit (marked infinity in fig. 7) which was used as a calibration datum. A larger version of the transmitter is being used in studies of edentulous subjects, and this results inextension of the range of IOD measurement to 10 or 15 mm, with a useful improvement in accuracy over the range 0-5 mm IOD. However, in the case of normal subjects, the improved range and accuracy of the larger transmitter is more than cancelled by much greater interferencewith the variable being measured. The normal transmitter is considerably smaller than
364
Q.H.Dibdin and X . J. G'rifiths
ones reported elsewhere: that of Bando et al. (197.2) was 32 x 14 x 8 mm. weighing 7 . 5 g with ba'tteries,while that of Joniot (1974) was 27 x 7.6 x 7.6 mm in size. Reduction of bulk was less important in Joniot's studies of edentulous patients, in contrast to most of ours and to those of Bando, where subject's had completeoralmostcomplete dentitions,leaving much less spacefor the transmitter. The resolution of the equipment was limited by the 'dead-band'widt'h of the pen recorder, being about four times better than the figures quoted above for accuracy. Frequency response of the receiver could be adjusted by means of a time constant in t'he output of t'he linear frequency meter, but in the case of potentiometric recorder output was limited to only about 2 Hz: in practice: however, this proved to be sufficient for most purposes. Theapparatushas been successfully used in several studies. Thesehave included recordings made overnight on a subject sleeping with and wit'hout the effect of tranquillizers, studies of t'he effect of posture on t'he value of IOD and of the way in which the jaws move during swallowing. In the example shown in fig. 'i movements due to speech. respiration and swallowing can be seen.
RBSUME Un systeme tblbmbtrique intra-buccal pour l'enregistrement continu du mouvement vertical de la mbchoire La mesure continuedel'bcart entre les arcs dentaires superieur et infbrieur, l'bcartdit interocclusal (EIO), est d'un inthrht en art dentaire. On discute les criteres pour executer ces mesures au moyen de la radiot616metrie. La conclusion obtenue est qu'il est nbcessaire d'avoir un transmetteur tres petit, qui porrait etre place dans l'8cart de la dent molaire, afin de reduire au minimum l'interference avec la fonction normale; d'autres facteurs de construction ont rapport a la nbcessite d'obtenir une stabilite suffisante de frbquence, de laquelle dependla precision de mesure. On dbcrit un transmetteur satisfaisant ces conditions requises, qui btait susceptible ii la valeur instantanbe de E10 par le changement de frbquence, produit quand un objet en metal (plombage dentaire, couronne en or, tour en fil mbtallique en short-circuit, ou piece de ferrite) dans un arc dentaire se deplapait par rapport au transmetteur dans l'autre arc. On a mesure lee erreurs causbes par les mouvements laterauxet protrusifsdela mbchoire. One construction soignee ainsi que l'emploi des condensateurs de haute qualit6 en matiere cbramique ant' result6 en un transmetteur d'une bonne stabilite de frequence ( i.0,03% en 10 heures, O,OP%,deg C ) et de petites dimensions (10 mm x 7 mm x 5 mm). On presente un exemple illustrant les mourements de EIO, causes par l'ingurgitation, la parole et la respiration.
ZUSAMMENFASSUNG Ein intra-orales Telemetriesystem fur kontinuierliche Registrierung senkrechter Kieferbewegung Von einem gewissen Interesse in der Zahnheilkunst ist die kontinuierliche Messung des abstands zwischen dem oberenund dem unteren Zahnbogen, d.h. des sogenannten interokklusalen Abstands (IOA). Es werden Kriterien zur Ausfiihrung solcher Messungen mittels Radiotelemetrie besprochen. Es wird geschlossen, dass ein Sender, welcher genug klein ist um in den Kieferzahnabstand zu passen, benotigt mird, um die Storung der normalen Funktion so klein als moglich zu machen; andere Konstruktionsfaktoren bezeihen sich auf die Moglichkeit, eine entsprechende Frequenz zu erhalten, worauf die Messungsgenauigkeit abhangt. Es wird ein die obigen Anspruche erfullende Sender beschrieben, welcher den Xomentanwert von 10-4mittels der Frequenzhnderung prufte, die entstand, wenn ein Metallgegenstand (Zahnplombe, goldene Krone, kurzgeschlossene Drahtwindung oder ein Ferritstuck) in einem Zahnbogen in Beziehung auf den Sender in dem anderen Bogen sich bewegte. Es sind die v a n seitlichen und Protrusions-Kieferbewegungen verursachten Fehler gemessen warden. Eine sorgfaltige Konstruktion, sowie die Anwendung von hochstgradigen keramischen Kondensatoren ergaben einen Sender van guter Frequenz-stabilitat
Telemetry of Vertical J a w Alovernent
365
( i 0,030,b wahrend 10 Std., 2 0,0'7,'Grad C) und kleinen Abmessungen (10 mm x 7 mm X 5 mm). Es wird ein Beispiel gegeben, welches die IOA-Bewegungen illustriert, melche durch Schlucken,
Reden und Atmen verursacht werden.
REFEREXCES ASDERSOS,D., 1972, W i r e l e s s V o r l d , 78, 38. BASDO,E., FUKCSHIMA, S.,KAWABAT-4, H., and KOHSO,S.: 1972, J . Prosth. Dent., 28, 483.
DIBDIN,G. H., 1974, Lab. Pract., 23, 563. DCXBURY, A . J., and ROTHWELL, P. S.,1973, J . Dent. Res., 52, 932 (Abstract). J.,and RSXFJORD, S . P., 1962, J . Prosth. Dent., 12, 895. GARNICK, GEISSLER, P. R.,1972, in P r o c . B r . Soc. f o r the Study of Prosthetic Dentistry, April 1970 (Bristol: John Wright) p. 21. GRIFFITHS, M.J., and DIBDIK,G. H., 1973, J . DeTzt. Res., 52, 934 (Abstract). JONIOT, B., 1954, J . Prosth. Dent., 31, 4. Ksap, F. J., R'ICHARDSOK, B. L., and BOGSTAD, J., 1970, J . Prosth. Dent., 24, 148. LAIRD,W . R'. E., MASSON,G., DAVIES, E. H., and VOX FRAUNHOFER, J. -A., 1971, Biorned. E n g n g , L o n d . , 6, 504. ?IIACKAY, R. S.,1970, Bio-medicalTelemetry, 2nd edn., (London and S e w York: John Wiley) p. 102. PARFITT, G. J., 1961, J . Periodont., 32, 102. PROVOST, W . A . , and TOWLE,H. J., 1972, J . Prosth. Dent. 27, 377. THOJISOS, J. C., and MACDOKALD, X. S.,1969, J . Biomech., 2, 319.
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An intra-oral telemetry system for the continuous recording of vertical jaw movement
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1975 Phys. Med. Biol. 20 355 (http://iopscience.iop.org/0031-9155/20/3/001) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 130.102.42.98 This content was downloaded on 03/10/2015 at 10:44
Please note that terms and conditions apply.
PHYS.MED. BIOL.,
1975, VOL. 20,
NO.
3, 355-365. @ 1975
An Intra-oral Telemetry System for the Continuous Recording of Vertical Jaw Movement G. H. DIBDIX,? PH.D and M. J. GRIFFITHS, M.B., B.s., F.D.S, The M.R.C. Dental Unit? and The University of Bristol Dental School, Lower Maudlin Street, Bristol BS1 2LY, England Received 19 August 1974, inJinal f o r m 22 October 1974 Continuous measurement of the separation between upper and lower dental arches, the so-called interocclusal distance ( I O D ) , isof interest in dentistry. Criteria for making such measurements by radio telemetry are discussed. It is concluded that a transmitter small enoughto fit in a molar tooth gapis necessary in order to minimize interference withnormal function;other design factors are related toobtaining adequate frequency stability, on which measurement accuracy depends. A transmitter fulfilling these requirements is described which sensed the instantaneous value of IOD by the frequency change produced when a metallic object (dental filling, gold crown, shorted turn of wire or piece of ferrite) in one dental arch moved relative t o the transmitter in the other. Errors due to lateral and protrusive jaw movements were measured. Careful design and the use of high grade ceramic chip capacitors resulted in a transmitter of good frequency stability ( f 0.030/6 in 10 h, f 0 . 0 2 ~ o / o cand ) small size (10 x 7 x 5 mm). An example is given illustrating IOD movements due to swallowing, speech and respiration.
ABSTRACT.
1. Introduction
Cont'inuous measurementsof the separation bet'ween upper and lower dental arches, the so-called interocclusa,l distance or 'freeway space', are of interest in st'udying many problems in dentistry. Approaches to the problem of making such measurements have varied from the use of unwieldy mechanical devices (Garnick and Ramfjord 1962, Knap, Richardson and Bogstad 1970, Provost and Towle 1972), which musthave interfered greatly with function, to recent more sophisticated methods. These have included: opto-electronic (Geissler 1972, Duxbury and Rothwell 1973), and inductive devices (Laird, Manson,Davies and vonFraunhofer 1971), which nevertheless required rods or wires to project from betweenthe lips; and Fukushima, t'elemetry systems (Thomson and MacDonald 1969, Bando, Kawabata and Kohno 1972, Joniot 1974), which removed the necessityfor wires and, as long as the bulk was kept small, should have int'erferedless with normal function. This paper presents a discussion of some of the important factors governing measurement of interocclusal distance (IOD) by radio telemetry, together with a description of equipment which has been designed with these in mind. 2. Requirements 2.1. Range
The equipment was mainly intended for studies of the resting value of IOD, itsvariationwithtimeandtheeffecton it of changes inbodyposture, 13
356
G. H . Dibdin and
X .J.
Griflths
situations of stress, type of sleep and so on. For these a range of IOD measurement from 0 to 5 mm seemed adequate from preliminary studies; most speech patterns also appeared t o lie within this range, which was therefore taken as the minimum required. 2 . 2 . Accuracy
It is difficult to define the accuracy requirement; a mere indication of IOD wouldbeuseful, althoughreasonableprecision is clearlydesirable.Greater absolute accuracy is required at thelower values O f IOD to make their percentage error reasonably small. An uncertaint'y corresponding to i 5% of reading, or rf: 0.1 mm, whichever is greater, was t'herefore considered adequate. 2.3. Resolution It is desirable to have greaterresolution than implied by theabove accuracy figures, in ordert o make it possible to compare patternsof small IOD movements, as distinct from measuring absolute values. 2.4. Frequency response Under circumstances where, for example, the IOD goes to zero with a resultant sudden tooth contact, there is a rapid deceleration which, if it is to be reproduced faithfully, needs a frequency response up to perhaps 20 or 30 Hz. However, for adequate reproductionof the more gentle movements involved in studiesof the resting value of IOD, a response up to two hertz isgenerally quite adequate. 3. The choice of measuringsystem It is desirable that t'he measuring system should not affect the freedom of movement of the jaws in any way, which in case strain gauges or potentiometers, coupled to the upper and lower jaws simultaneously, are excluded because of the elastic and frictiona'l constraints they impose. There remains the possibility of mounting a transmitter in or on one dental or arch,itsoutput being modified according to separation,byinductive capacitative int'eraction with a component of the other dental arch. Because of the high dielectric constant of water and of soft tissue generally, a capacit'ative dist'ance transducer is subject to severe inaccuracies produced by humidity fluct'uat'ions and movement of the cheek and tongue. The remaining choice is between different types of inductive transducer. Of these, the balanced'variablepermeance'differentialtransformer (see for example in the case of IOD studies Parfitt 1961) is the most accurate and linear, but would require a core attached toone arch tomove wit'hin acoil att'ached to the other, inhibit'ingfreedom of lateral and protrusive movement of the jaw. It is advantageous for the information on IOD to be obtained in the form of a change of transmitt'er frequency,since calibration is then independentof signal strength. It is possible to do this without the limitation of a differential transformer, by making use of the frequency change produced when a magnetic or conductive material moves towards or away from the field of the transmittercoil. This was the system chosen for the present work, and briefly described elsewhere
Telemetry of Vertical Jaw Movement
357
(Griffiths and Dibdin 1973). The transmitter consisted of asmalloscillator (fig. 1) mounted on one dental arch with its coil lying in the occlusal plane, while a non-penetrating ‘core’ was attachedtotheotherarch.The ‘core’ consisted either of high permeability ferrite, increasing the inductance of the coil according to its proximity, or else an amalgam restoration, gold crown or shorted turnof wire, in which case the effective inductance was decreased. The circuit diagram of the transmitter is shown in fig. 2. The main design requirements were (1) minimalinterference withnormalfunction and (2) good
t”-l Receiver
Fig. 1. The telemetry transmitter (T) in a first molar tooth space of the lower jaw, its transmission frequency (f)being altered according to the proximity of the ‘core’ (C) consisting of ferrite, a metallic restoration or a shorted turnof wire. 2.2 -3.3K
Fig. 2. The transmitter circuit : a Hartley oscillator with centre-tapped coil.
frequency stability against all variables other than the one under study. The influence of these factors on the design (frequency of operation, method of construction and so on) are dealt with below. 4. Transmitter design factors
4.1. Interference with function In the absence of external wires, etc., the only factors associated with the transmitter which might interfere with function, and so modify the measurements themselves: are the transmitter bulk and weight. This becomes a more
358
G . H . Dibdin and M . J . Grifiths
important factor if, as in the present case, studies are not confined to denture wearers. It was considered desirable to limit the bulk of the transmitter to about that occupied by molar tooth, so-thatit would be possible to fit it in a good percentage of the commonly found gaps left by routine extraction of a permanent molar. Alternatively, the device had to be small enough to attach to the buccal (cheek) side of a permanent molar tooth, so that it projected as littleas possible. It was also considered desirable to limit the transmitter weight to less than that of an average molar tooth, to avoid influencing the dynamic balance of the jaw unduly. 4.2. Frequency stability
Because of the small frequency shift produced by the variable under study (about 10 kHz in 500 kHz, or 2y0)the frequency had tobe stabilized to within f 100 Hz ( k 0.02yo)for the period of unattended measurement, to reduce errors below f 1% of full scale deflection. This was enough to give the measurement accuracy discussed in section 2 . 2 , taking account of the nonlinearity of the system.The following arethemaindisturbing variables which hadto be considered. (a) Xoft tissue movement. Movement of cheek and tongue cause variation in the stray capacitance of the transmitter, shifting the transmission frequency. This can be minimized by making the tuning capacitance very large in comparison with anystraycapacitance, which in turn necessitatesarelatively low frequency of operation. These considerations led to a choice of transmitter frequency in the region of 500 kHz, with a tuning capacitance of 1500-2200 pF. Under these conditions effects due to soft tissue movement were found Do be negligible. (b) Moisture penetration. A transmitter contained within the mouth must be reasonably insensitiveto frequency drift or damage dueto moisture penetration. The large value of tuning capacitance already described in (a) is a help in this respect, but it is clearly desirable to encapsulate the whole transmitter in as impermeable a covering as possible. However, it is well known that all plastics slowly absorb moisture, the water uptake byepoxy resins being from 0.5 to 1yo by volume after prolonged exposure, and rathermore in the case of cold setting acrylics, Mackay (1970) has shown that moisture uptake for paraffin waxes is, in contrast, verysmall indeed, andsuggests that epoxy encapsulated telemetry transmitters be coated with wax before use to improve their water repellent properties. Early transmitters in the present work were totally encapsulated in aspecial electrical grade of epoxy resin (Araldite MY753 with HY951 hardener). More recently, however, the following procedure has been found simpler and, in view of Mackay’s work, preferable. The complete transmitter-battery system was encapsulated in capacitor grade insulation wax, and then coated with a thin layer of epoxy or cold setting acrylic for mechanical strength. The wires for an external on/off switch were brought to the surface as a bifilar spiral to extend the path length for any moisture tracking preferentially down the wires. This later design has the great advantage that the outer case can be cut away,
Telemetry of Vertical Jaw Movement
359
without damage to the circuitry, and a new battery inserted before re-coating it with plastic. Any voids or cracks in thewax were resealed after encapsulation by placing the area concerned close to the tipof a warm soldering iron. (c) Change in oral temperature. Oral temperature shows some variation due to mouth breathing, etc.,even in healthy subjects.It was found that the temperature of a transmitter in place in the mouth varied by as much as & 1 'c over the period of measurement, necessitating atemperature coefficient of frequency for the transmitter better than & 0.02y0 per degree C, in order to obtain the accuracy required. Until recently this was difficult to achieve in a small low frequency transmitter as required in (a), because of the difficulty of fitting a capacitance as large as 1500 pF andof the required temperature stability, into so small a space. However, with the adventof much smallerNPO grade ceramic chip capacitors it is now possible to obtain a packing density of about 300 p F per mm3 using these high stability components. Frequency stability obtained in the present design was usually in the range & 0 ~ 0 1 - 0 ~ 0 2per ~ 0 degree C, measured with the aid of a constant temperature water bath and a digital frequencymeter,although occasionally transmittershad coefficients which were lower. (d) Battery voltagelbattery age. To minimize slow drift during an experiment it is important that the variationof transmitter frequency with battery age is low. The circuit design chosen had the effect of limiting current drain to between 0.15 and 0.3 mA, given a possible battery life of between 70 and 140 h, using a fully charged RM212H Mallory cell, the smallest available. As can be seen from the battery discharge curves shown in fig. 3 this arrangement led to a greatly 1.4 \ 0.14 mA -
0.26 mA
'
;1.0 -
1.0 rnA
1
0 ~ 8 20~ " 40" " 60" " EO " " 100 ~
120
140
Time (h)
Fig. 3. Voltage-time discharge curves for the Mallory cell type RM212H showing the improved voltage plateau obtained at low discharge currents; this gives better transmitter frequency stability against time.
reduced rate of voltage drop comparedwith that obtained at the 1.5 mA discharge rate(battery life 8-12 h) used byotherauthors(Thomsonand MacDonald 1969, Joniot 1974). I n addition, theinclusion of the 2.2-3.3k collector series resistor shown in fig. 2 stabilized the working point, making the frequency itself less susceptible to battery voltage variation. I n a test on a transmitter completely immersed in normal saline a t 37 5 0.1 'c, the measured frequency drift due to both battery ageing and moisture uptake was less than k 0.03y0 in a 10 h period. Although
360
G. H . Dibdin and
AM.J . Grifiths
ideally this could be even lower, it was adequate to make overnight measurements a possibility without excessive baseline drift. (e) Sensitivity to lateral and protrusive jaw movements. Since it is desirable for the transmitter and 'core' to be as smallaspossible, protrusiveorlateral excursions of the jaw a t constant IOD are likely to cause some change in t'heir mutualinteraction,resultinginmeasurementerrors a t eachvalue of IOD. Fig. 4 shows the errors for a small transmit'ter,measured with a set-up designed
Lateral ( x ) andprotrusive
( y ) dlsplacement (mm)
Fig. 4 . Change in apparent interocclusaldist'ance (IOD) due t o lateral movements (a). and protrusive movements( y ) of the jaw a t three fixed values of true IOD.
t o allow lateral and protrusive movements x and y: a t constant values of IOD. It can be seen that the errors start to become serious a t excursions of more than 2-3 mm, depending upon separation. However, at IOD values less than 1 mm or so, where the percentage error is greatest. interlocking of the teeth tends to inhibit such movement'. Moreover: where the 'core, is in the form of a row of restorations or gold crowns, t'he error due to protrusive (and to a lesser extentlateral)movements can be furtherreducedbyasuitable choice of geometry, involving maximal extension of the coil perpendicular to the line of theserestorations(i.e.towards cheek andtongue):withoutthe device becoming noticeable to the wearer. Constructional details of transmitter Referring to thecircuit diagram infig. 2 the components used were as follows : Transistor: Microelectronics type MT4103 subminiature epoxy. Resist'ors : Ardentehearingaid type RSXOO. Capacit'ors: 1.5-2-2 n F : Vitramon type VJlPlOA XPO grade ceramic chip. 330 pF : Vitramon type VJ0808A NPO gradeceramicchip. Coil : 2 x 28 turns of 48 swg enamelled copper wire, wound as a bifilar coil on a 'i x 10 mm former, waxed and removed. All transmitter components except coils and bat'tery were cemented lightly together in a small rectangular pack 4 x 3 x 2 mm, and interconnections were made using a soldering iron with a 0.8 mm diameter bit. Four wires were left projecting from this pack for connection to the battery, which was positioned immediately a,longside,and t o the coil which was placed on top of t'he combined assembly. Connections to the batterywere made either with conducting paint 5.
Telemetry of Vertical Xovement Jaw
361
(Silver Dag, fromAcheson Colloid, Ltd.) or by means of small pressure contacts. Capacitor wax was melt'ed into the assembly, ta'king care not' t o overheat the of battery, after which it was dip-coated with acrylic or epoxy resin. A pair twisted wires mas brought to t'he surface for switching the power on and off. The met'hod of mounting t'he transmitter in a tooth gap with the required positional stability is shown in fig. 5 . A replica of the st'andard transmitter n
Transmitter
Undercuts
Fig. 5 . Method of mounting the transmitter in a tooth gap. The split retainer was placed in the tooth gap with t'he transmitterposit'ioned in the recess shown, holding the two halves of the split retainer apart so that they located in natural undercuts on t'he adjacent teeth.
shapewasfirstmadeinself-curingacrylicresin, then coatedwith silicone grease or ot'her release agent. X plaster cast of the subject's t'eeth was similarly coated around t'he tooth gap to be used, and into this was pressed the transmitter replica, surrounded by a part'ly cured doughy mass of a dental plastic (Trim, from H. J. Bosworth and Co., Chicago). When cured, this assembly was held firmly in position bJ- the naturally undercut contoursof neighbouring teeth. A vert'ical saw cut through the mid-line of the transmitter replica and the surrounding plastic enabled the assembly to be removed in two halves. Extraction of the replica pieces left a split retainer (fig. 5 ) accurately contoured to the teeth and the transmitter. The ret'ainer was placed inthe subject's toot'h gap, and the actual transmitter inserted. This gave good positional stabilit'y without undue pressure being exerted on the surrounding tissues. 6. Transducer calibration Calibration of the receiver output in terms of IOD was achieved by getting the subject to bite gently into different thicknesses of impression wax, and noting the corresponding output deflection.Measurement of t'heseparationcaused by these wax bites on t'he plaster models of the subject"s teeth then gave t'he IOD and receiver output'. Calibrationchecks requiredrelationshipbetween could be made during a' recording session by asking the subject to close his teeth together, and then to open his mouth as wide as possible. i . The receiver
A block diagram of t,he receiver is shown in fig. 6. The 500 kHz radio signa,l was picked up on a loop aerial worn around the subject,'s neck. This provided
G. H . Dibdin and N . J . Griflths
362
the input for a miniature battery-powered RF preamplifierbasedupon the Mullard 470 kHz I.F. module type LP 1166. The preamplifier was individually coils for 'open', tuned t o each telemetry transmitter by peaking the three tuning 500 kHz
Preampllfler (LP 1166)
1.
Mlxer/IF
10-20kHz
Arnpllfler/ l,miter
-1 1
Frequency divider
L
1-2 kHz Frequency meter
(+Io)
Stereo-cassette
Loudspeaker
+ I
Commentary
I
Chart recorder
Fig. 6. The receiver. The 500 kHz signal was converted t o an IF of 10-20 kHz, frequency divided and fed t'o the linear frequency meter. The 1-2 kHz signal could also be recorded onto stereo casset'te tape, together with a commentary, and replayed as indicated by the pecked lines for later chart recorder display.
'midway' and 'closed' values of IOD. To facilitatetuning,t'he preamplifier carried a miniature moving coil indicator which showed output signal level and also gave an indication of battery condition. The preamplifier output was fed via a lightyeight,low impedance coaxial lead to the main receiver (which could therefore be located some distance away), where it wasmixedwitht'he local oscillatorsignalin the mixer amplifier 6 signal (fig. 6) a t a n (MullardTAD 110). This gave a square wave output the intermediatefrequencyvarying from 10 t o 20 kHzdependingupon instantaneous value of the subject'sIOD. The following circuit (IC type FJJ141) divided t'he frequency by 10 t o give a 1-2 kHz square wave output suitable for recording on one channel of a stereo cassette tape recorder as described elsewhere (Dibdin 1974); a commentary was recorded on the ot'her channel. Finally, Ohis frequency modulated signal was replayed as indicated by t'he pecked lines in met'er (Anderson 1972) which gave an fig. 6, and used t'o drive a linear frequency output voltageproportional to frequency,forcalibrationinterms of the subject's IOD. 8.
Discussion
By following the design criteria which havebeen discussed, transmitters have been produced with the following specifications : 1Ox7x5mm Dimensions : including battery. 750 mg Weight - : 480-530 kHz. Frequency of operation : Frequency deviation : F 5 kHz (typical).
Telemetry of Vertical Jaw Movement Frequencystability
:
363
(a) withtemperature:betterthan i 0.02y0 per degree C . (b) with time: better than f 0.03y0 over a 10 h periodwhenimmersedinnormalsaline at 37
OC.
Battery current: 0.15-0.3 mA. Battery life : (R" 212H) 40 minimum. h Error in IOD measurement due to lateral and protrusive movement : approximately 7% a t IOD = 2 mm for excursions of k 2 mm, increasing for greater excursions. Frequency response : 0-30 Hz with oscilloscope output'. 0-2 Hz with pen recorder output'. Useful measurement' range : 0-6 mm approx. As would be expected from itsmode of operation, the response of the system is nonlinear. This can be seen from the sample trace given in fig. 7, which shows a drop in sensitivitya t larger values of IOD ; usually t'heuseful range of measurement was about 0-6 mm. Inaccuraciesdue to temperature fluctuations and
F"
Fig. 7. A sample of IOD data obtained using the t,elemetry system described. Examples of swallow (S), speech (Sp) and small rhythmic variations due t o respiration (R) can be seen. The parts marked C(C) and C ( 0 ) are calibration checks made during the course of a recording, when the subject was asked to close his teeth toget'her for a, few seconds, and then open as wide as possible.
drift were about k 0.05 mm or k 2.5% of reading (whichever was greater) up to anIOD of 3 mm, increasing to f 6% of reading a t a nIOD of 5 mm. IOD values greater than 12 mm or so caused no further deflection, giving an upper limit (marked infinity in fig. 7) which was used as a calibration datum. A larger version of the transmitter is being used in studies of edentulous subjects, and this results inextension of the range of IOD measurement to 10 or 15 mm, with a useful improvement in accuracy over the range 0-5 mm IOD. However, in the case of normal subjects, the improved range and accuracy of the larger transmitter is more than cancelled by much greater interferencewith the variable being measured. The normal transmitter is considerably smaller than
364
Q.H.Dibdin and X . J. G'rifiths
ones reported elsewhere: that of Bando et al. (197.2) was 32 x 14 x 8 mm. weighing 7 . 5 g with ba'tteries,while that of Joniot (1974) was 27 x 7.6 x 7.6 mm in size. Reduction of bulk was less important in Joniot's studies of edentulous patients, in contrast to most of ours and to those of Bando, where subject's had completeoralmostcomplete dentitions,leaving much less spacefor the transmitter. The resolution of the equipment was limited by the 'dead-band'widt'h of the pen recorder, being about four times better than the figures quoted above for accuracy. Frequency response of the receiver could be adjusted by means of a time constant in t'he output of t'he linear frequency meter, but in the case of potentiometric recorder output was limited to only about 2 Hz: in practice: however, this proved to be sufficient for most purposes. Theapparatushas been successfully used in several studies. Thesehave included recordings made overnight on a subject sleeping with and wit'hout the effect of tranquillizers, studies of t'he effect of posture on t'he value of IOD and of the way in which the jaws move during swallowing. In the example shown in fig. 'i movements due to speech. respiration and swallowing can be seen.
RBSUME Un systeme tblbmbtrique intra-buccal pour l'enregistrement continu du mouvement vertical de la mbchoire La mesure continuedel'bcart entre les arcs dentaires superieur et infbrieur, l'bcartdit interocclusal (EIO), est d'un inthrht en art dentaire. On discute les criteres pour executer ces mesures au moyen de la radiot616metrie. La conclusion obtenue est qu'il est nbcessaire d'avoir un transmetteur tres petit, qui porrait etre place dans l'8cart de la dent molaire, afin de reduire au minimum l'interference avec la fonction normale; d'autres facteurs de construction ont rapport a la nbcessite d'obtenir une stabilite suffisante de frbquence, de laquelle dependla precision de mesure. On dbcrit un transmetteur satisfaisant ces conditions requises, qui btait susceptible ii la valeur instantanbe de E10 par le changement de frbquence, produit quand un objet en metal (plombage dentaire, couronne en or, tour en fil mbtallique en short-circuit, ou piece de ferrite) dans un arc dentaire se deplapait par rapport au transmetteur dans l'autre arc. On a mesure lee erreurs causbes par les mouvements laterauxet protrusifsdela mbchoire. One construction soignee ainsi que l'emploi des condensateurs de haute qualit6 en matiere cbramique ant' result6 en un transmetteur d'une bonne stabilite de frequence ( i.0,03% en 10 heures, O,OP%,deg C ) et de petites dimensions (10 mm x 7 mm x 5 mm). On presente un exemple illustrant les mourements de EIO, causes par l'ingurgitation, la parole et la respiration.
ZUSAMMENFASSUNG Ein intra-orales Telemetriesystem fur kontinuierliche Registrierung senkrechter Kieferbewegung Von einem gewissen Interesse in der Zahnheilkunst ist die kontinuierliche Messung des abstands zwischen dem oberenund dem unteren Zahnbogen, d.h. des sogenannten interokklusalen Abstands (IOA). Es werden Kriterien zur Ausfiihrung solcher Messungen mittels Radiotelemetrie besprochen. Es wird geschlossen, dass ein Sender, welcher genug klein ist um in den Kieferzahnabstand zu passen, benotigt mird, um die Storung der normalen Funktion so klein als moglich zu machen; andere Konstruktionsfaktoren bezeihen sich auf die Moglichkeit, eine entsprechende Frequenz zu erhalten, worauf die Messungsgenauigkeit abhangt. Es wird ein die obigen Anspruche erfullende Sender beschrieben, welcher den Xomentanwert von 10-4mittels der Frequenzhnderung prufte, die entstand, wenn ein Metallgegenstand (Zahnplombe, goldene Krone, kurzgeschlossene Drahtwindung oder ein Ferritstuck) in einem Zahnbogen in Beziehung auf den Sender in dem anderen Bogen sich bewegte. Es sind die v a n seitlichen und Protrusions-Kieferbewegungen verursachten Fehler gemessen warden. Eine sorgfaltige Konstruktion, sowie die Anwendung von hochstgradigen keramischen Kondensatoren ergaben einen Sender van guter Frequenz-stabilitat
Telemetry of Vertical J a w Alovernent
365
( i 0,030,b wahrend 10 Std., 2 0,0'7,'Grad C) und kleinen Abmessungen (10 mm x 7 mm X 5 mm). Es wird ein Beispiel gegeben, welches die IOA-Bewegungen illustriert, melche durch Schlucken,
Reden und Atmen verursacht werden.
REFEREXCES ASDERSOS,D., 1972, W i r e l e s s V o r l d , 78, 38. BASDO,E., FUKCSHIMA, S.,KAWABAT-4, H., and KOHSO,S.: 1972, J . Prosth. Dent., 28, 483.
DIBDIN,G. H., 1974, Lab. Pract., 23, 563. DCXBURY, A . J., and ROTHWELL, P. S.,1973, J . Dent. Res., 52, 932 (Abstract). J.,and RSXFJORD, S . P., 1962, J . Prosth. Dent., 12, 895. GARNICK, GEISSLER, P. R.,1972, in P r o c . B r . Soc. f o r the Study of Prosthetic Dentistry, April 1970 (Bristol: John Wright) p. 21. GRIFFITHS, M.J., and DIBDIK,G. H., 1973, J . DeTzt. Res., 52, 934 (Abstract). JONIOT, B., 1954, J . Prosth. Dent., 31, 4. Ksap, F. J., R'ICHARDSOK, B. L., and BOGSTAD, J., 1970, J . Prosth. Dent., 24, 148. LAIRD,W . R'. E., MASSON,G., DAVIES, E. H., and VOX FRAUNHOFER, J. -A., 1971, Biorned. E n g n g , L o n d . , 6, 504. ?IIACKAY, R. S.,1970, Bio-medicalTelemetry, 2nd edn., (London and S e w York: John Wiley) p. 102. PARFITT, G. J., 1961, J . Periodont., 32, 102. PROVOST, W . A . , and TOWLE,H. J., 1972, J . Prosth. Dent. 27, 377. THOJISOS, J. C., and MACDOKALD, X. S.,1969, J . Biomech., 2, 319.
