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Table of Contents
Year : 2017  |  Volume : 7  |  Issue : 2  |  Page : 80-86

An introduction to the clinically relevant analysis of mastication

1 Department of Prosthodontics, Rajiv Gandhi University of Health Sciences, Bengaluru, Karnataka, India
2 Department of BioResearch, BioResearch Associates, Inc., Milwaukee, WI, USA
3 Department of Dentistry, Dental College and RI, Bengaluru, Karnataka, India
4 Department of Medicine, SIMS and RC, Shivamoga, Karnataka, India

Date of Web Publication9-Aug-2017

Correspondence Address:
Prafulla Thumati
# 296, Orofacial Pain Center, Katriguppa Main Road, Banashankari 3rd Stage, Bengaluru - 560 085, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jid.jid_29_17

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The process of mastication is an essential function for the survival of dentate organisms and has long been a subject of the study in the dental literature. PubMed lists 11,202 references to articles on mastication from 1914 to the present. Moreover, dentistry pays too little attention to a patient's ability to chew food. The teeth that we fill, extract, replace, and by orthodontics move are critical to the mastication of food. Of course, there are many other structures and organs involved as well. Mastication is the initial step in the digestive process of all dentate subjects and necessary for good nutrition and health. Thus, an understanding of mastication is very important in Dental Medicine. Mastication can be analyzed in three ways: (a) analyzing the movements of the mandible, (b) analyzing the activity of the masticatory muscles (electromyography studies) or c) analyzing the results of the mastication process (chewing particle size analysis). Each of these approaches has been studied separately in the past, but the simultaneous analysis of the movements and the muscle activity is the more revealing approach. A discussion is presented here to illustrate how the combination of electrognathography and electromyography can be recorded through a highly sophisticated hardware and software system using a personal computer. Analyzing masticatory movements with simultaneously recorded muscle activity to reveal muscle coordination has become a technique that can be carried out in the average dental practice. The results of these studies can help us diagnose temporomandibular joint internal derangements, identify other temporomandibular disorder conditions, and design prosthetic restorations that function. More uniquely, this process can also reveal the quality of a patient's masticatory function before any treatment and indicate incremental improvement after treatment.

Keywords: Electrognathography, electromyography, mastication analysis, temporomandibular disorders

How to cite this article:
Thumati P, Radke JC, Thumati RP, Thumati PP. An introduction to the clinically relevant analysis of mastication. J Interdiscip Dentistry 2017;7:80-6

How to cite this URL:
Thumati P, Radke JC, Thumati RP, Thumati PP. An introduction to the clinically relevant analysis of mastication. J Interdiscip Dentistry [serial online] 2017 [cited 2023 Mar 30];7:80-6. Available from: https://www.jidonline.com/text.asp?2017/7/2/80/212602

   Clinical Relevance to Interdisciplinary Dentistry Top

Understanding Mastication Analysis is critical for helping an individual to attain good health as Mastication is important for the survival of an individual.

   Introduction Top

The dynamics of moving lower jaw can be expressed by its position (relative to the maxilla), its velocity, its acceleration and the smoothness of its movements, which are all produced by the active and passive forces generated by joints, ligaments, and muscles acting on the mandible.[1],[2],[3],[4],[5],[6]

The resultant forces and torques move the mandible with 6 degrees of freedom (DOF) in relation to the skull, three translations (vertical, antero-posterior, and lateral) and three rotations (yaw, pitch and roll).[7] If the condyles and the interposed disks of both joints maintain articular contact all the time with the fossa (no distraction), translation of the condyle in a direction perpendicular to the articular surface of the temporal bone is restricted. Furthermore, if both joints are assumed to be connected rigidly through the mandibular symphysis, the rotation of the mandible about an anteroposterior axis is also limited to motions away from the mid-sagittal plane. Thus, whereas the mandible can be moved within 6 DOF, the extent of some of those motion degrees are very limited.

Electrognathography (EGN); records and displays mandibular movements using a jaw tracking magnet and a flux-sensing array. Three dimensions of movement can be measured: Vertical, anterior/posterior, and Lateral translations.[8] EGN + electromyography (EMG) studies can be carried out using the model JT-3D Jaw Tracker together with the BioEMG III (BioResearch, Inc., Milwaukee, USA). Similar equipment is also manufactured by Myotronics (Seattle, USA); although, it lacks the sophisticated mastication analysis program (BioPAK) developed jointly by BioResearch and Professor Takao Maruyama of Japan.

Each muscle contraction is associated with force, which is expressed in its magnitude, point of application (the insertion), and its orientation to the origin. Each muscle can produce a translation force on the lower jaw only along its line (or lines) of action and a rotation about an axis more or less perpendicular to it, running through the jaw's center of gravity and together represent two DOF,[6] one translation and one rotation. Hence, the number of DOF of a system of muscles depends on the number of independent lines of action. A fan-shaped muscle, the temporalis, can apply a force to its insertion in a wide variety of directions, depending on which part of the muscle contracts. Jaw movements caused by the masticatory muscles are guided by both active and passive structures. A mathematical model of muscle contraction dynamics widely accepted in the musculoskeletal analysis is called Hill's Muscle Model.[9]

The muscles of mastication are involved in moving the mandible while chewing, swallowing and during the speech. They include the temporalis, masseter, medial pterygoid, (elevators), the lateral pterygoid, and the anterior digastric (depressors), all of which develop from the mesoderm of the first brachial arch and hence are innervated by mandibular division of 5th cranial nerve. In conjunction with the above muscles, the buccinators (VII), suprahyoid muscles including the posterior digastric (VII), stylohyoid (VII), mylohyoid (V), geniohyoid (XII), and the eight muscles of the tongue (X and XII) all contribute to mastication. The infrahyoid muscles, the sternohyoid, omohyoid, sternothyroid, and thyrohyoid (innervated by the ansa cervicalis, C1–C3) stabilize the hyoid bone and actively contribute to the facilitation of both mastication and deglutition. The masticatory system is very complex, and chewing is a highly coordinated task for the central nervous system (CNS). The task of mastication should be learned and the adult it usually does not even begin to mature until about the age of 3 years.[10] It is accomplished by a multiplicity of muscles through several nerves [Figure 1].
Figure 1: (a) Temporalis (b) Medial and Lateral Pterygoids (c) Massetric (d) Suprahyoid

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The significance of masticatory (chewing) motion can be understood by considering three important aspects of it

The purpose of the average chewing pattern (ACP) is to cancel the random variations within the chewing pattern sequence, reveal the size and shape of the underlying average pattern of function and provide a measure of the variability of the pattern (the standard deviation) [Figure 2]. Conveniently, the overall shape of the ACP is usually distorted by stomatognathic dysfunction [Figure 3]. Three changes are most commonly associated with dysfunction; (1) the size of the ACP decreases, (2) the velocity is reduced, and (3) the variability of the chewing pattern is increased by dysfunction.[8],[11] The duration of the chewing cycle (cycle time) is extended by most types of masticatory dysfunction as the patient chews more slowly and more tentatively.[12],[13] When subjects successfully adapt to their dysfunction one or more of these factors (size, shape, or speed) can be ameliorated.[11] Masticatory function after very successful adaptation sometimes appears to be within normal limits., with only an objectively measurable increase in exteroceptive suppression (silent periods [SPs]) occurring during mastication. For a patient with no complaints or without excessive SPs, no treatment may be indicated, even in cases where dysfunction has previously been very well documented.
Figure 2: A normal subject's left and right average chewing pattern of gum chewing. The black line patterns represent the mean patterns of 500 normal subjects scaled in size to this individual for comparison. Note: This subject's average chewing pattern closely matches the mean normal patterns in the frontal, sagittal, horizontal and velocity views. The green vertical bars indicate that the vertical dimensions for these two examples are within 2 standard deviations of the mean normal value

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Figure 3: A dysfunctional subject's left and right average chewing pattern of gum chewing: The black line patterns represent the mean patterns of 500 normal subjects scaled in size to this individual for comparison. Small patterns, Tight angles and too much Variability. The two red vertical bars indicate that the vertical dimension in these two examples are both more than 2 standard deviations below the mean normal value (small patterns)

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The process of averaging removes the variability from the ACP view that is visible graphically in the raw movement data.[14] Consequently, the excessive variability that is caused by dysfunction is most visually obvious in data graphs that show the raw data. Since every cycle must include open-close in the vertical dimension, the vertical motion tends to be less visually indicative of dysfunction. However, the Horizontal View, combining the A/P and Lateral dimensions, provides an excellent view of excessive variability in the raw data.[8] [Figure 4].
Figure 4: Horizontal X-Y graphs of raw movement data: (a) Dysfunctional. (b) Normal. Because the dysfunctional patient cannot find any efficient chewing path, no two cycles even look similar. As a result, you see a pattern of continuous random paths rather than the consistent pattern of the normal subject. Of course, a fracturing bolus does not result in the very consistent pattern of gum due to the unpredictability of its breakdown.

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The significance of masticatory muscle function can also be understood by averaging

The average chewing cycle (ACC) of the masseter and temporalis muscles can be calculated by averaging EMG activity cycles also over a sequence of 10–15 chewing cycles.[8],[11] To accomplish that, a complete sequence must be divided into individual cycles and continuous instantaneous rms values calculated for each muscle for each point in every cycle throughout a sequence. Then, 10–15 cycles are averaged to create an ACC of the muscle activity. This process removes the random variations between individual cycles, reveals the underlying shape of the contraction pattern, provides a measure of variability (standard deviation) and reveals the hierarchy of muscle activity between the four muscles. It is particularly interesting to observe the masseter and temporalis activities since they are the largest muscles that actively apply most of the closing forces that crush food.[15]

A normal pattern of muscle activity can easily be demonstrated by recording a Class I asymptomatic subject during chewing. The most active muscle being the working side masseter muscle (W-Mm), followed by the working temporalis muscle (W-Ta), followed by the nonworking temporalis muscle (NW-Ta), and finally, the nonworking masseter muscle (NW-Mm) [Figure 5a]. It is relevant that when chewing on one side normally the contralateral side is given a rest. This allows the healthy patient to randomly chew left and right, back and forth, without fatiguing any of their muscles.
Figure 5a: Normal subject chewing gum on the left side (typical pattern) and on the right side (slightly altered). The working masseter peaks at the highest level followed by the working temporalis, nonworking temporalis and finally the nonworking masseter

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In the presence of a malocclusion or an internal derangement (ID), the mean area per cycle (summed muscle activity) is increased (usually due to longer cycles), but the Peak Amplitude is usually decreased. The hierarchy of the activity distribution (Ta vs. Mm) is more likely altered by a maxillo-mandibular skeletal mal-relation than by a simple tooth-related malocclusion. Furthermore, the variability of an individual's muscle pattern is increased with muscle dysfunction.[11] With dysfunction, the ACC is modified more for cases that are not well adapted than for those that are well adapted, but the ACC is still modified in all cases of adaptation to an aberrant condition [Figure 5b].
Figure 5b: A patient with masticatory dysfunction, poorly adapted when chewing gum on the left side (a) and better adapted when chewing gum on the right side (b). The hierarchy of intensity is rearranged on both sides for this patient with proportionately more nonworking activity apparent. With poor adaptation the muscles are usually inhibited and show less activity, but with good adaptation they often work harder to compensate for the dysfunction. The area under each curve is proportional to the amount of work done.

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The ACC shows a patient's characteristic pattern of muscle function, including; a) the intensity of each muscle's average contraction, and b) the hierarchy of the activity from the most active to least active muscle (W-Mm, W-Ta, NW-Ta, and NW-Mm), which represents the coordination pattern. In a superimposed view of each muscle's activity, the inconsistency of the activity is visually depicted [Figure 6].
Figure 6: An example of the superimposed view of the electromyography activity all of the cycles overlapped revealing graphically the increase in variability that occurs with dysfunction. While normal subjects have consistent patterns of muscle activity during chewing, in the dysfunctional subject the activity is far more variable, with nonworking side activity sometimes exceeding working side activity (as in this case for Mm and Da)

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In the dysfunctional subject, this hierarchy of muscle can change rather dramatically. In cases of severe muscle dysfunction, the nonworking side muscles are often working more than the working side muscles. In mild dysfunction, the increased variability may be only in the one or two muscles necessary to adapt to a less than ideal situation. In severe dysfunction, the variability will be very high because the patient simply cannot find any coordination pattern that works well. For example, although the working temporalis is very active in the dysfunctional subject [Figure 6], there is no discernable pattern to that muscle activity.

Muscle dysfunction and pain usually accompany temporomandibular disorders (TMDs), whether in the form of an occlusal interference, an occlusal breakdown, or a skeletal misalignment problem. While masticatory muscle pain is common in TMD, it is very rare that a painful masticatory muscle has a primary myopathy or neuropathy. That finding almost never occurs! The pain is usually secondary to a problem or condition outside of the painful muscle. The phenomenon of pain is referred from the true site of the disorder to an often remote other location has been well documented.[16],[17],[18] Just eliminating occlusal interferences or a maxillo-mandibular skeletal mal-alignment will often allow the restoration of good muscle function, creating a more peaceful neuromusculature, and leading to a neuromuscularly oriented maxillo-mandibular condition.

The significance of silent periods during gum chewing

Exteroceptive suppression (the SP) is produced by a nociceptive (protective) monosynaptic (local) neural reflex.[19] A consistently occurring SP during chewing usually indicates one or more unavoidable tooth contacts. SPs can occur either during the end of closure as the teeth approach centric occlusion or in the beginning of the opening with the departure from centric occlusion. An SP represents hard evidence of an unavoidable occlusal interference, which can be reduced or eliminated by Immediate Complete Anterior Guidance Development.[11] The absence of SP does not necessarily mean zero interfering contacts because some patients are able to avoid them. However when an SP is frequently present, it implies that the subject is unable to avoid at least one interfering premature tooth contact.

The SP in the elevator muscles of the masticatory system suppresses elevator activity locally without any input from the CNS. SPs are most commonly recorded only from the masseter and the temporalis, but that is due to those muscles' accessibility to surface EMG, not because they are the only muscles involved. SPs occur when teeth contact with sufficient energy to stimulate the periodontal fibers attached to the specific tooth, and are typically the result of a premature contact during chewing. The contact may be on the working or nonworking side, but the effect of a significant contact will affect all elevator muscles bilaterally [Figure 7]. Occasional SPs of not more than 20% (<3 SP in 15 cycles) of the cycles is considered within normal limits and can usually be observed in some subjects within any thoroughly representative group of asymptomatic control subjects. There are other sensors within the masticatory system that can elicit SP responses, such as the stretch receptors in muscles, but during chewing a soft bolus (gum) the sensors in the periodontal fibers are the dominant initiators.
Figure 7: The silent period can be triggered by interfering tooth contacts during gum chewing. The left pane (a) is an expanded view showing a partial silent period followed by a complete cessation of activity of all four muscles about 40 msonds later. The small arrow denotes a very slight tooth contact which is not sufficiently strong enough to create a full silent period. The large arrow indicates a stronger contact producing a full cessation of activity in all four muscles (for ~25 msonds). The right pane (b) demonstrates that in some patients with occlusion related masticatory dysfunction nearly every cycle includes a silent period

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Types of masticatory function

There are three general types of function that have been observed; (1) Normal-normal includes patients with a normal chewing movement pattern and normal muscle patterns and hierarchy, (2) normal-abnormal includes patients also with a normal movement pattern, but with abnormal muscle function and with an altered contraction hierarchy (these patients are usually well adapted to a dysfunction, but may also have muscle pain) and (3) abnormal-abnormal with an abnormal movement pattern and abnormal muscle function (poorly adapted to a dysfunction). It is worthwhile to note that there is no documented case of a patient with an abnormal movement pattern and normal muscle function. Muscle is accommodative in nature, and the CNS often uses the musculature to adjust for structural deviations. Muscle is quickly adaptive but pays a price, usually with pain with strained exertion.

   Summary Top

Mastication is an oral motor behavior reflecting CNS commands and many peripheral sensory inputs that modulate the rhythmic jaw movements. The action of masticatory muscles during chewing varies between subjects in amplitude, onset timing, and the duration of the chewing cycle. However, it is possible to recognize similarities between muscle actions. Wide variations (within and between individuals) can be explained by differences related to individual occlusal contact features and specific musculoskeletal morphology. The mandible moves not only vertically during mastication, but also antero-posteriorly and especially laterally. These horizontal movements are the most important for the reconstruction of missing teeth.

In a chewing cycle, the approach to tooth contact should be relatively consistent. The chewing pattern is learned function, which is altered by the loss of teeth and often changed by various restorations. Since tooth guidance has an enormous influence on muscle activity during chewing and swallowing, it is advisable to make restorations compatible with the functional movement patterns of the patient rather than expect the patterns of the mastication to adapt to the newly installed restorations.

   Conclusions Top

By recording incisor-point motion and at least some of the associated EMG activity that drives it, the dentist can have a better understanding of the functional or dysfunctional status of a patient's masticatory system. From this discovery, a more valuable treatment can be planned, and the degree of success of the treatment can also be objectively verified. Those patients with the worst masticatory dysfunction are the ones who can benefit the most. The objectives of dental treatment can and should be advanced to include enhancing chewing capacity with complete comfort as much or more than just creating a beautiful smile.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Pickerill HP. On the production of narrow jaws by the mastication of tough and fibrous foods: Synopsis of communication. Proc R Soc Med 1914;7:92-100.  Back to cited text no. 1
Miller FR. The cortical paths for mastication and deglutition. J Physiol 1920;53:473-8.  Back to cited text no. 2
Stilson HH. Mastication and Saliva. J Natl Med Assoc 1920;12:34-54.  Back to cited text no. 3
Koolstra JH, van Eijden TM, Weijs WA, Naeije M. A three-dimensional mathematical model of the human masticatory system predicting maximum possible bite forces. J Biomech 1988;21:563-76.  Back to cited text no. 4
Koolstra JH, van Eijden TM. Three-dimensional dynamical capabilities of the human masticatory muscles. J Biomech 1999;32:145-52.  Back to cited text no. 5
Koolstra JH. Dynamics of the human masticatory system. Crit Rev Oral Biol Med 2002;13:366-76.  Back to cited text no. 6
Nägerl H, Kubein-Meesenburg D, Fanghänel J, Thieme KM, Klamt B, Schwestka-Polly R. Elements of a general theory of joints 6. General kinematical structure of mandibular movements. Anat Anz 1991;173:249-64.  Back to cited text no. 7
Radke JC, Kull RS, Sethi MS. Chewing movements altered in the presence of temporomandibular joint internal derangements. Cranio 2014;32:187-92.  Back to cited text no. 8
Hill AV. The heat of shortening and dynamics constants of muscles. Proc R Soc Lond B Lond Royal Soc 1938;126:136-95.  Back to cited text no. 9
Wilson EM, Green JR. The development of jaw motion for mastication. Early Hum Dev 2009;85:303-11.  Back to cited text no. 10
Kerstein RB, Radke J. Average chewing pattern improvements following Disclusion Time reduction. Cranio 2017;35:135-51.  Back to cited text no. 11
Hansdottir R, Bakke M. Joint tenderness, jaw opening, chewing velocity, and bite force in patients with temporomandibular joint pain and matched healthy control subjects. J Orofac Pain 2004;18:108-13.  Back to cited text no. 12
Buschang PH, Hayasaki H, Throckmorton GS. Quantification of human chewing-cycle kinematics. Arch Oral Biol 2000;45:461-74.  Back to cited text no. 13
Harold RJ. Mathematics: A Human Endeavor. 3rd ed. Cambridge: W. H. Freeman; 1994. p. 547.  Back to cited text no. 14
Hagberg C. The amplitude distribution of electromyographic activity of masticatory muscles during unilateral chewing. J Oral Rehabil 1986;13:567-74.  Back to cited text no. 15
Campbell CD, Loft GH, Davis H, Hart DL. TMJ symptoms and referred pain patterns. J Prosthet Dent 1982;47:430-3.  Back to cited text no. 16
Wright EF. Referred craniofacial pain patterns in patients with temporomandibular disorder. J Am Dent Assoc 2000;131:1307-15.  Back to cited text no. 17
Markman S, Khan J, Howard J. Elusive dental pain. Gen Dent 2010;58:e62-7.  Back to cited text no. 18
Ahlgren J. The silent period in the EMG of the jaw muscles during mastication and its relationship to tooth contact. Acta Odontol Scand 1969;27:219-27.  Back to cited text no. 19


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5a], [Figure 5b], [Figure 6], [Figure 7]


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