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An Introduction to Mastication Analysis in General Practice

March 1, 2013
by Larry Hill, DDS


Mastication is an essential function for survival of dentate organisms and has long been a subject of study in the dental literature.1-3 For dentists, understanding mastication is of utmost importance. The teeth we repair, restore, move or periodically extract and replace, masticate food for our patients. This mastication provides the initial step in the digestive process necessary for survival of the human organism.

There are basically three ways of analysing mastication: analysing the movements, analysing the muscle activity (EMG studies) or analysing the results of the mastication process (chewing particle analysis). This paper will focus on the analysis of mastication movements.

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With the appearance of the computer and development of sophisticated hardware and software by John Radke and others, analysing masticatory movements and even simultaneous recording of muscle activity and muscle coordination has become something that can be carried out in the average dental practice. The results of these studies can help us diagnose TMJ derangements, identify TMD causes and design even better prosthetic restorations. Shimshak and DeFuria showed that TMD patients have, on average, 112% more digestive complaints (in terms of cost of medical treatment) than a comparable normal group.4 It is important, therefore, to analyse our patients’ ability to masticate. The results of these studies have overturned some long held tenets of dentistry.

In my office Electrognathology (EGN) studies are carried out using the Jaw Tracker (BioResearch Inc., Milwaukee, USA). Similar equipment is also manufactured by Myotronics (Seatle, USA) although they lack the sophisticated mastication analysis program developed jointly by BioResearch and Professor Takao Maruyama of Japan and used with the Jaw Tracker.

To record masticatory movements a small magnet is placed on the outside of the lower incisor teeth using a sticky wax (with a deep bite the magnet can be placed on the lingual surface). A headgear containing bilateral sensors senses the position and movement of the magnet in three dimensions and records this movement with an accuracy of 0.1 mm. This headgear is placed on the patient and aligned. Besides mastication analysis this equipment can be used to measure and record range of motion, motions of the jaw during speech, freeway space measurements (with extreme accuracy), velocity (discussed below) and bite registrations. Used simultaneously with Joint Vibration Analysis (JVA) one can see exactly in the opening cycle where jaw joint vibrations occur (Fig. 1).

The patient chews according to directions using varying boli; gum or a harder licorice. The patient’s movements are recorded by the software program which then creates an average chewing cycle which is represented graphically. The cycle can be compared to a data base of over five hundred “normal subjects.”

A Mastication Cycle is comprised of three phases: Opening Time (OT), Closing Time (CT) and Occlusal Time (OcT). Normal cycle time varies from 600-900 milliseconds. Of this total cycle time, OT is roughly 1/3, CT is slightly more than 1/3 (as the bolus is compressed) and OcT is a bit less than 1/3. The movements of the jaw are presented graphically in three views: Frontal, Sagittal and Horizontal. The Turning Point (TP) is the point at which the jaw ceases opening and begins closing. This TP is shown in millimeters in three dimensions relative to CO. (The entire record begins with the patient in Centric Occlusion with teeth together). The Terminal Chewing Position (TCP) Point is the point at which the teeth cease moving together (maximum bolus compression). It is also shown relative to CO.

Let’s look at a representation of an average mastication trace using gum as a bolus. Gum is the softest constant bolus available. As the bolus becomes harder the movements become more erratic as the bolus is moved around. Most diagnostic traces are done using gum; if someone cannot chew gum, they cannot chew! This trace illustrates a right-sided mastication: (Fig. 2)

Note that both opening and closing movements are convex to each other and the Turning Point is on the side the patient is chewing on. This will become important when we look at TMJ dysfunction and its effect on Mastication patterns (Fig. 3).

The patient is instructed to begin chewing with the teeth in contact and the operator observes 15-20 cycles and then ends the capture function. (These 15-20 movements can be analysed individually or analysed using the Average Chewing Pattern (ACP) provided by the software.)

In this ACP trace of a normal patient you can observe the convexity of both opening (red) and closing (blue) movements and that the terminal point is on the working side. The black line is the average pattern of 500 normal subjects. This is provided by the software as a reference (Fig. 4).

This is the summation of the average data for the above Mastication trace provided by the Maruyama Mastication software. The values are within the normal parameters.

Note the Terminal Chewing Position. This position is 0.3mm + – 0.1mm. This is a surprising finding; the teeth do not touch while masticating! A gum bolus is probably the smallest bolus possible. With food the bolus would be much larger and the TCP would be even larger.

Our North American diet is a relatively soft diet. Where, therefore, does most of our tooth wear come from if it’s not from food abrasion or tooth to tooth contact during mastication? Most tooth wear comes from erosive phenomena such as GERD or dietary input (acidic erosion) or from parafunctional movement: clenching and bruxing. The author believes this parafunctional movement produces the largest portion of the wear we observe in most of our patients (Fig. 5).

If we look again at the normal frontal view of a chewing cycle (above left) we note that from the Terminal Chewing Position the jaw drops vertically. Most lateral movements occur below this with most movement occurring at about 50% opening. There is virtually no lateral movement with the teeth in contact or near contact. Evans and Lewin carried out mastication analysis of a group of San people in the Kalahari dessert.5 This group of nomadic hunter/gatherers eat a diet very much coarser than our diet yet had much the same pattern as we do with only slightly more lateral movement. A multi-cycle recording of their chewing pattern is shown (Fig. 6).

Where, therefore, does the emphasis of centric occlusion and grinding movements originating from that position derive (something that we all ask our patients to do)? It has very little to do with chewing food. As it turns out it is very important for parafunctional movements. A good cuspid rise disclusion of the posterior teeth in lateral parafunctional movement is of paramount importance. Kerstein and Radke, in studies using simultaneous T-Scan (a computer bite pressure recording device) and EMG, has shown that this disclusion of the posterior teeth reduces the prolonged muscle activity of Masseter and Temporalis muscles.6 This prolongued muscle activity is probably the source of much of our TMD patients’ pain and discomfort that is not Temporo-Mandibular Joint based (Fig. 7).

The sagittal view is added here for your interest. This is the normal mastication trace shown above. The black line is, again, the composite norm for five hundred patients inserted for comparison. The sagittal view shows the opening and closing jaw movements from the Terminal Chewing position. This view is not as useful as the frontal view but it can help diagnosing tooth interferences in dysfunctional patients.

Let’s turn now to a trace of a dysfunctional patient. Dysfunctional mastication traces can have several causes: TM joint pathologies, muscle pathology, tooth interferences or tooth pain avoidance. Mastication analysis can be another tool in diagnosing these problems (Figs. 8 & 9).

Note in this left chewing pattern that the (red) opening line has lost the conv
exity of a normal trace. The closing line (blue) is convex. The turning point remains on the working side although it has moved slightly away from the ideal and toward the midline. Note the cycle times are close to normal (indicating good adaptation) although the deviations are larger. The Turning Point is (vertically) shorter than normal. This patient has right disk displacement with reduction. Mastication traces show the effect of the TM joint opposite to the working side. One can imagine that as the patient opens the movement of the jaw toward the working side is affected by the opposite joint translating and as this happens the Turning Point is brought closer to the midline and the arc is turned from convex to concave. This limitation to normal movement is brought about as the disk impedes the movement and then is recaptured. There are four frontal patterns possible as outlined by Maruyama: (Fig. 10)

The Frontal-1 (F-1) pattern is normal as we have discussed. The F-2 pattern is that of a disk displacement with reduction which we saw in the patient above. The F-3 pattern is that of a disk displacement without reduction that is acute or recent. The lack of reduction of the opposite joint impedes the translational movement on that side and moves the Turning Point across the midline away from the working side. The F-4 pattern is that of a disk displacement without reduction that is chronic or long standing. Here the adaptability of the Temporomandibular Joint complex is in play. The Turning Point has come back toward the midline (but still on the wrong side) and the arcs have regained their convexity. This pattern represents an adapted condition.

As in any classification system the gradual transition from one classification to another (i.e. F-2 to F-3) can be blurry, since it is really a continuous process. Nevertheless, this system works well in day to day analysis.

Velocity is another useful parameter to analyse with mastication traces. As the Jaw Tracker records the movement the velocity of the magnet attached to the lower jaw is recorded in mm/sec. This recording is presented in a graphic form: (Fig. 11)

This normal mastication velocity pattern shows the opening movement (red) accelerate as the jaw drops and then decelerate as the turning point is reached. On closing the reverse occurs. The closing jaw accelerates rapidly and then slows as occlusion is reached. On closing the rapid acceleration occurs early and then slows as the teeth come closer together. This velocity graph is shown over a vertical axis showing mm of opening (Fig. 12).

Compare the normal velocity recording with that of a dysfunctional patient shown here: a top velocity of 50 mm/sec compared to the maximum velocity above of close to 200 mm/sec. Also, the opening range has decreased. The appearance of this trace would indicate that something is dysfunctional. This would not be obvious except to the most astute observer. Velocity is an excellent way to track improvements in a patient’s function as therapy is carried out.

Mastication Analysis is simple procedure which can be completed by a dental assistant along with a battery of other jaw movement recordings, in about 10 minutes. The results of these tests can be a useful diagnostic tool and can also be used to monitor post treatment changes. Through these studies several fundamental tenets of dentistry have been overturned:

(1) Teeth rarely contact when chewing or swallowing, therefore most of our tooth wear comes from parafunctional movements or erosion.

(2) There is little lateral movement close to the intercuspal position while masticating. Most lateral movement occurs while the teeth are relatively farther apart.

(3) Incisal guidance has little function in mastication except when anterior interferences cause a disruption of the pattern. Incisal guidance, however, does have a strong role during the production of speech. Evans and Lewin studied an African tribe who removed their anterior teeth for cultural display.7 Their mastication recordings match ours very closely indicating anterior guidance is not used during normal mastication.

(4) Mastication appears to have no preferred side (as in right or left handedness). If your patient does have a preferred side to chew on it means that there is some limitation to chewing on the other side. There may be joint pathology on the side they prefer since that condyle is the non-translating condyle in the chewing pattern. The patient prefers the chewing side that avoids translational movements of a pathological joint complex or some other cause. A right side preference means that the right TMJ cannot translate properly (as would occur in a left sided chewing). Other causes of having a preferred side may be occlusal interferences (which would be apparent in the mastication trace), muscle pathology or even a sensitive tooth.OH

Oral Health welcomes this original article.

 REFERENCES

1. The Chewing Apparatus. An Electromyographic Study of the Action of the Muscles of Mastication and its Correlation to Facial Morphology. Moller E., Acta Physiol Scand Suppl. 1966;1 229-280.

2. Chewing Pattern Analysis in TMD Patients with and without Internal Derangements: Part I, Kuwahara t., Bessette R., Maruyama T., J Craniomandibular Prac. 1994, Vol 13(1) 8-14.

3. Development of an Ultra-Miniaturized Inertial Measurement Unit for Jaw Movement Analysis During Free Chewing, Zhuohua L. et al.,Journal of Computer Science 2010, 8, 896-903.

4. Health Care Utilization by Patients with Temporomandibular Joint Disorders, D.G. Shimshack and M. DeFuria, J. Craniomandibular Practice 1998, Vol. 16 (3) , 185-193.

5. Some characteristics of mandibular movement in a group of San, W.G. Evans and A. Lewin, J Dent Ass. of S. Africa, 1986, 41,543-548.

6. The Effect of Disclusion Time Reduction on Maximal Clench Muscle Activity Levels, Kerstein, R., Radke, J., J. Craniomandibular Prac., Jul 2006, 24(3), 156-165.

7. Lower incisors and Mandibular movement, W.G. Evans and A. Lewin, J. Dent Ass of S. Africa 1987 42. 469-74.


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1 Comment » for An Introduction to Mastication Analysis in General Practice
  1. Teresa says:

    My comment is that of a “patient” not a medical professional so I’m not sure that this comment is helpful or appropriate. I have been struggling with an issue of food feeling as though it is going into my sinus area when I eat, and this has been happening for the last year or more. Just lately I have come to believe it is because my most functional molar on my left side was removed and I began chewing on my right. Lately I have been playing with it a bit when I chew and feel that I “chew backwards” on my right with my food being “pushed up” rather than down. I have searched everywhere and can’t find anything on this. My dentist didn’t mention this would be a problem. Is this something that happens?

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