tooth contact during chewing

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DOI: 10.1177/00220345570360011301

1957 36: 21J DENT RESD.J. Anderson and D.C.A. Picton

Tooth Contact During Chewing

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TOOTH CONTACT DURING CHEWINGD. J. ANDERSON, PH.D., M.Sc., B.D.S., AND D. C. A. PICTON, B.D.S.

Physiological Laboratory and Dental Department, Guy's Hospital, London, England

INTRODUCTION

THE main justification for the treatment known as bite rehabilitation orlocclusal equilibration appears to be the assumption that the teeth come

into centric ocelusal contact during chewing. If this occurs and if the oc-clusion is normal, the masticatory loads are distributed (not necessarilyequally) throughout the whole dental arch. If the teeth do not come intocontact during chewing, but remain separated by food, then ocelusal equilibra-tion seems to be justified only in gross malposition of the teeth, or in indi-viduals who indulge in bruxism.

The problem of ocelusal contact during chewing has been investigatedby only a few workers. Hildebrand,' using radiographic technics, concludedthat at the commencement of the chewing movement there is slight lateralgliding of the lower denture against the upper, and at the termination of themovement "the mandible reaches the ocelusal position after eventual glidingof the lower denture against the upper." Jankelson, Hoffman and Hendron'reported results obtained by completing an electrical circuit between opposingteeth, which showed that contact during chewing did not occur or was insig-nificant. In some instances it appeared at the first swallow, in others onlyduring the second or third swallow. The record shown in their paper was ob-tained from one subject eating apple. Yurkstas and Emerson,3 using a similartechnic on 12 subjects with artificial dentures showed a surprising frequencyof tooth contact both on the working and balancing sides. The subjectschewed meat and bread sandwiches.

The series of experiments to be reported here was designed to investigatethe frequency of tooth contact in the natural dentition during chewing. Tenmale subjects of ages ranging between 20 and 34 years provided the experi-mental data. All except one (Subject 1) were student volunteers, who werenot chosen on the basis of their dental condition; the only requirement beingthe presence of amalgam restorations in one pair of opposing posterior teeth.In all cases the dentition was complete or nearly so.

METHOD

It was decided to record contact between the teeth by completing an elec-trical circuit through them using a small voltage applied to the circuit todeflect one beam of a double-beam oscilloscope. In order to relate the fre-quency of contact to the number of chewing movements, electromyographic

Received for publication July 13, 1955.

21



22 ANDI)lS;UN ANI) 1IITOJDeUNs. 1 cbrua~rv, 195 7

records fromii one oLf the masseter muscles were obtained on the other oscillo-scope beami. Vine gauge silver or stainless-steel wires were eiubedded inamalgam in existing tooth cavities and were carried on to the buecal surfaceof the teeth without interfering with normal occlusion. In some cases anadditional wire was let into a suitable part of the ocelusal surface of one ofthe existing amtalgams if the wires on the buecal surfaces failed to make a

A.

B.~~~~~~~~~~~~~~~~~.O

4...

D.

B.

Fig. 1.-Oscilloscope records of electrical activity in the masseter on the chexwing sideupperr tracing) and contact between the teeth on the opposite side. Tooth contact is shownby an elevation of the lower tracing. A, Subject 1. Biscuit; B, Subject 2. Carrot; C, Subject 6.Apple; D0, Subject 8. Bread; E, SubJect 10. Meat.

satisfactory contact after adjustment. In every case great care was taken toensure that the wires allowed unhindered movement and closure of the jaws.If an occlusal wire was necessary, a slot was provided for it in the amalgamso that it did not interfere with occlusion.

When an experiment was contemplated, fine insulated leads were attachedto the buceal extensions of the wires embedded in the teeth and passed out of

. -. I . , . , I , " 1. I . 1 -7 1 , , -, , , I "., , , " T, 11,



Volume 36 TOOTH CONTACT DURING CHEWING 23Number I

the mouth to complete the rest of the circuit. Electromyographic records weretaken with surface electrodes applied by suction to the skin over the masseter,and the potentials obtained were suitably amplified. The tooth wires werecarefully adjusted to make contact with the teeth in centric occlusion only;the slightest lateral movement breaking the circuit. This was checked afterevery chewing sequence. The critical nature of the contact and the finenessof the leads from the chosen teeth made it necessary for the records to betaken with the subject chewing on the opposite side of the mouth. The elec-tromyographic records were taken from the chewing side.

Five food materials were chosen for the experiments. These were: short-bread biscuit, raw carrot, apple, cooked meat, and crustless bread. They weregiven in 0.5 inch cubes and the subjects were instructed to chew them withoutincisor biting and to give a signal as soon as the material had been swallowed.

RESULTS

Typical records are shown in Fig. 1. In most subjects contact was leastfrequent with biscuit, none of them making contact on every thrust. Withthe other materials, most subjects brought their teeth into contact for morethan one-half the thrusts, some for all the thrusts with every material. Whencontact occurred it was always more frequent toward the end of the chewingsequence. The results are shown graphically in Fig. 2, the number with eachpoint referring to a particular subject. The means and standard deviationsof the data for each subject were computed and are available from the authors.

It will be observed that Subject 6 executes many more chewing move-ments for every material than the other subjects. There was no gross dentalabnormality which might be held to account for this. His arches were com-

plete save for the loss of 14 and the occlusion was only a mild example

of Angle's Class II, division 1.The frequency of contact in this series is surprisingly high, and in only

2 of the subjects were consistently low values recorded with all materials.It is noteworthy that the duration of each contact increased toward the endof the chewing sequence.

DISCUSSION

The object of the experiments reported here was to determine the fre-quency of contact between the dental arches during chewing, contact beingregistered with the teeth in centric occlusion. The wire used to complete theelectrical circuit between the opposing teeth was approximately 0.5 mm. indiameter and in all cases the smallest possible voluntary gliding movementwith the teeth in contact broke the circuit. In the empty mouth the methodtherefore records centric occlusal contact and an extremely narrow range ofgliding movements out of centric occlusion.

During chewing, the food was on the side opposite to that used for record-ing contact and it is therefore possible that the teeth may have been separated



ANDERSON AND PICTON J. l). Res.February, 1957

A.

()

U

200

1U

B.

15

10'

CHEWSC.

rig. 2.-The relation between the number of chewing movements and the number ofcontacts. The sloping line shows the direction which would be taken by the points if contactoccurred with every chewing movement. The number with each point identifies the subject.A, biscuit; B, carrot; C, apple.

24



Volume 36Number 1

TOOTH CONTACT DURING CHEWING 25

by food on one side while coming into contact on the other. This is con-sidered unlikely for several reasons. Attempts by the subjects to break theelectrical contact while keeping the teeth together on the other side always

20 &QU

15 Z0U

D.

CHEWSE.

Fig. 2.-Cont'd. D, bread; E, meat.

failed. This shows that the jaws are not easily tilted. In some of the sub-jects, separation of the teeth on the chewing side with paper 0.0015 inch thickbroke the contact on the other side while in others paper twice as thick wasnecessary. This shows that although tilting can occur it is only very slight.If it is conceded that contact can be recorded on one side while the other side



96 ANDERSON AND PICTON J. D. Res.16d W ~~~~~~~~~~~~~~~~~~~~~~~February,1957

is slightly separated, then during chewing, this separation would have to bemaintained in spite of the fact that the main muscular effort tended to over-come it. It seems unlikely that any of the food materials used in this inves-tigation, except biscuit, could be capable of this.

In view of the surprisingly high frequency of contact shown by most sub-jects, the teeth were examined for evidence of wear. This was most markedin Subject 1 who made contact on every thrust with all the foods except bis-cuit. This subject, aged 34, was approximately 12 years older than the others.Signs of considerable wear were seen in all the teeth, even the third molars,and the facets suggested that he indulged in nonfunctional grinding of theteeth. Most of the other subjects showed some attrition but it was not pos-sible to grade it accurately. None of the subjects showed any gross ortho-dontic abnormalities, the occlusion conforming with Angle's Class I, or insome cases showing a tendency toward Class II or III. Subject 9, who broughthis teeth into contact most infrequently of all the subjects, showed a consider-able incisor overbite, the lower incisors touching the palate, having drifted backfollowing the loss of 6 16 . The upper incisors just came into contact withthe gingiva in front of the lower incisors. The subject was not conscious ofthis fact.

SUMMARY

1. Contact between opposing teeth during chewing was recorded electri-cally in 10 subjects with 5 food materials.

2. The results confirm the hitherto unsupported assumption by manyperiodontologists that the teeth make contact during chewing.

3. The teeth came into contact for more than one half the chewing thrustsin most subjects. In some subjects every thrust made contact, but this wasnever the case with biscuit.

4. The results strongly suggest that when contact occurred it was centricocclusal contact over the entire arch..

Our thanks are due to the subjects for their co-operation and to the Nuffield Founda-tion for a grant to one of us (D. J. A.) which has supported this work.

REFERENCES

1. Hildebrand, G. Y.: Skand. Arch. Physiol., supply, vol. 61., Studies in the MasticatoryMovements of the Lower Jaw, 1931.

2. Jankelson, B., Hoffman, G. M., and Hendron, J. A.: J. A. D. A. 46: 375-386, 1953.3. Yurkstas, A. A., and Emerson, Wv. H.: J. Pros. Dent. 4: 168-174, 1954.



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