Etiology of functional disturbances in masticatory system
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lecture for Post Grad. students (Courtesy Management of Temporomandibular Disorders and Occlusion by Jeffrey P Okeson)
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Etiology of functional disturbances in masticatory system
- 1. Etiology of Functional Disturbances in the Masticatory System
- 2. Etiologic Considerations in Temporomandibular Disorders No single etiology that accounts for all signs and symptoms Only one therapy of a disorder = treatment is quite effective Multiple treatments for the same disorder = none of the suggested therapies will always be effective 1/5/2018 2
- 3. Etiologic Considerations in Temporomandibular Disorders Two explanations for these findings: The disorder has multiple etiologies and no single treatment can affect all the etiologies the disorder is not a single problem but represents an umbrella term under which there are multiple disorders In the case of TMD, both these explanations are true 1/5/2018 3
- 4. Etiologic Considerations in Temporomandibular Disorders Numerous factors can contribute to TMD: Factors that increase the risk of TMD are called predisposing factors Factors that cause the onset of TMD are called initiating factors Factors that interfere with healing or enhance the progression of TMD are called perpetuating factors In some instances, a single factor may serve one or all of these roles 1/5/2018 4
- 5. Etiologic Factors Underlying Temporomandibular Disorders 1/5/2018 5
- 6. The Occlusal Condition As An Etiology Of Temporomandibular Disorder Early concept = occlusion is the most important contributing factor Recent concept = occlusal factors play little to no role Controversial 1/5/2018 6
- 7. Trauma As An Etiology Of Temporomandibular Disorder Trauma to the facial structures can lead to functional disturbances in the masticatory system Greater impact on intracapsular disorders than on muscular disorders Two general types: Macrotrauma is any sudden force that can result in structural alterations, such as a direct blow to the face Microtrauma is any small force that is repeatedly applied to the structures over a long period of time. Activities such as bruxism or clenching can produce microtrauma to the tissues that are being loaded (i.e., teeth, joints, or muscles) 1/5/2018 7
- 8. Emotional Stress As An Etiology Of Temporomandibular Disorder Emotional centers of the brain have an influence on muscle function Commonly plays an important role in TMD The patient’s emotional state is largely dependent on the psychological stress being experienced Circumstances or experiences that create stress are known as stressors. These can be unpleasant (like losing one’s job) or pleasant (like leaving for a vacation) 1/5/2018 8
- 9. Emotional Stress As An Etiology Of Temporomandibular Disorder The significant fact is that the body reacts to the stressor by creating certain demands for readjustment or adaptation (the “fight-or-flight” response) These demands are related in degree to the intensity of the stressor When a stressful situation is encountered, energy is generated within the body and must be released in some way 1/5/2018 9
- 10. Emotional Stress As An Etiology Of Temporomandibular Disorder There are basically two types of releasing mechanisms The first is external and is represented by activities such as shouting, cursing, hitting, or throwing objects Another source of external stress release is physical exercise This type of release is a healthy way in which to deal with stress 1/5/2018 10
- 11. Emotional Stress As An Etiology Of Temporomandibular Disorder A second mechanism by which stress is released is an internal mechanism Person releases the stress internally and develops a psychophysiologic disorder such as irritable bowel syndrome, hypertension, certain cardiac arrhythmias, asthma, or an increase in the tonicity of the head and neck musculature This type of stress-releasing mechanism is by far the most common It is important to remember that the perception of the stressor, in both type and intensity, varies greatly from person to person 1/5/2018 11
- 12. Emotional Stress As An Etiology Of Temporomandibular Disorder Increased levels of emotional stress experienced not only increases the tonicity of the head and neck muscles but it can also increase levels of nonfunctional muscle activity, such as bruxism or tooth clenching Emotional stress can also influence the individual’s sympathetic activity or tone In the presence of stress the capillary blood flow in the outer tissues is constricted, permitting increased blood flow to the more important musculoskeletal structures and internal organs 1/5/2018 12
- 13. Emotional Stress As An Etiology Of Temporomandibular Disorder The results are a cooling of the skin such as the hands Prolonged activity of the sympathetic nervous system can affect certain tissues such as the muscles Increased sympathetic activity or tone therefore represents an etiologic factor that can influence TMD symptoms 1/5/2018 13
- 14. Deep Pain Input As An Etiology Of Temporomandibular Disorder Common yet often overlooked concept is that sources of deep pain input can cause altered muscle function Can centrally excite the brainstem, producing a muscle response known as protective co- contraction Represents a normal, healthy manner in which the body responds to injury or threat of injury 1/5/2018 14
- 15. Deep Pain Input As An Etiology Of Temporomandibular Disorder This represents the body’s response to protect the injured part by limiting its use The limited mouth opening is merely a secondary response to the experience of the deep pain If the clinician does not recognize this phenomenon, however, he or she may conclude that the limited mouth opening is a primary TMD problem and treatment would be misdirected 1/5/2018 15
- 16. Parafunctional Activity As An Etiology Of Temporomandibular Disorder Parafunctional activities include clenching or grinding the teeth (referred to as bruxism) as well as various other oral habits Some of these activities may be responsible for creating TMD symptoms Subdivided into two general types: Diurnal (occurs through the day) nocturnal (occurs at night) 1/5/2018 16
- 17. Diurnal Activity Consists of clenching and grinding as well as many other oral habits This type of diurnal activity may be seen in someone who is concentrating on a task or performing a strenuous physical chore Masseter muscle contracts periodically in a manner that is totally irrelevant to the task at hand Most parafunctional activities occur at a subconscious level 1/5/2018 17
- 18. Diurnal Activity Therefore merely questioning the patient is not a reliable way to assess the presence or absence of these activities In many instances, once the clinician makes the patient aware of the possibility of these diurnal activities, he or she will recognize them and can than decrease them 1/5/2018 18
- 19. Nocturnal Activity Parafunctional activity during sleep is quite common Take the form of single episodes (referred to as clenching) and rhythmic contractions (known as bruxing) 1/5/2018 19
- 22. Nocturnal Bruxism Sleep 4 stages Stages 1 and 2 represent the early phases of light sleep Stages 3 and 4 represent the deeper stages of sleep The subject will then pass through a stage of sleep that is quite different from the others (REM) Approximately 80% of the sleep period of an adult is made up of non-REM sleep, with only 20% being REM sleep 1/5/2018 22
- 23. Nocturnal Bruxism Sleep Non-REM sleep is thought to be important in restoring the function of body systems REM sleep, on the other hand, seems to be important in restoring the function of the cerebral cortex and brainstem 1/5/2018 23
- 24. Nocturnal Bruxism Stages of sleep and bruxing events Controversial Lighter stages (1 and 2), of non-REM sleep Change from deeper to lighter sleep Bruxing may be closely associated with the arousal phases of sleep 1/5/2018 24
- 25. Nocturnal Bruxism Duration of bruxing events Vary greatly Uncertainty as to the number and duration of bruxing events that can create muscle symptoms 1/5/2018 25
- 26. Nocturnal Bruxism Intensity of bruxing events An average bruxing event involved 60% of the maximal clenching power before the person went to sleep Significant amount of force Maximal clench far exceeds the normal forces used during mastication 1/5/2018 26
- 27. Muscle activities and masticatory symptoms Forces of tooth contacts (3 times more) Direction of applied forces Mandibular position Type of muscle contraction Influences of protective reflexes 1/5/2018 27
- 28. Bruxism in children Very common finding Data on children are very scarce Rarely associated with symptoms self-limiting phenomenon 1/5/2018 28
- 29. THE PRECISE RELATIONSHIP BETWEEN OCCLUSAL FACTORS AND TEMPOROMANDIBULAR DISORDERS Pullinger et al concluded that no single occlusal factor could differentiate patients from healthy subjects Four occlusal features the presence of a skeletal anterior open bite retruded contact position to intercuspal contact position slides of greater than 2 mm overjets of greater than 4mm five or more missing and unreplaced posterior teeth 1/5/2018 29
- 30. The effects of acute changes in the occlusal condition and temporomandibular disorders Activities of the masticatory system Occlusal contacts and muscle hyperactivity 1/5/2018 30
Editor's Notes
- For example, if one refers to a medical textbook for suggested treatments of a disorder and only one therapy is listed, one usually will find that this treatment is quite effective if the textbook lists multiple treatments for the same disorder, the therapist can assume that none of the suggested therapies will always be effective
- The hypothalamus, the reticular system, and particularly the limbic system are primarily responsible for an individual’s emotional state. These centers influence muscle activity in many ways, one of which is through the gamma efferent pathways. Stress affects the body by activating the hypothalamic-pituitary- adrenal (HPA) axis, which in turn prepares the body to respond (through the autonomic nervous system)
- As far as the body is concerned, whether the stressor is pleasant or unpleasant is not important
- Although these activities are common and almost a natural response to stress, they are not generally well accepted in our society
- As previously mentioned, emotional stress is part of the human existence. We are built to handle stress, as demonstrated by the body’s fight-or-flight response to the challenges of our environment. The acute response to a sudden environmental challenge is healthy and necessary for survival—for example, running from a burning building or jumping away from an oncoming car. The issues of concern are not these acute responses but those that expose us to prolonged emotional stress, especially without the ability to escape—for example, negative work environments, unhappy marriages, or compromised family situations.
- Therefore it is reasonable to find a patient who is suffering with pain, such as toothache (i.e., necrotic pulp), to have limited mouth opening
- This clinical finding is common in many toothache patients. Once the tooth pain has been resolved, normal mouth opening returns
- Activities of the masticatory muscles can be divided into two basic types: functional, including chewing, speaking, and swallowing, and parafunctional (i.e., nonfunctional), including clenching or grinding the teeth (referred to as bruxism) as well as various other oral habits. The term muscle hyperactivity has also been used to describe any increased muscular activity over and above that necessary for function
- that are often performed without the individual’s awareness, such as cheek and tongue biting, finger and thumb sucking, unusual postural habits, and many occupation-related activities such as biting on pencils, pins, or nails or holding objects under the chin (a telephone or violin)
- Whether these activities result from different etiologic factors or are the same phenomenon in two different presentations is not known. In many patients both activities occur and are sometimes difficult to separate. For that reason clenching and bruxism are often referred as bruxing events.
- Evidence of cheek biting during sleep.
- Here the lateral borders of the tongue are scalloped, conforming to the lingual surfaces of mandibular teeth. During sleep a combination of negative intraoral pressure and forcing of the tongue against the teeth produces this altered tongue shape. This is a form of parafunctional activity
- This stage appears as a desynchronized activity in which other physiologic events occur, such as twitching of the muscles of the face and extremities, alterations in the heart rhythm and rate of breathing, and rapid movement of the eyes beneath the eyelids—thus the name REM sleep. It is during REM sleep that dreaming most commonly occurs. After the REM period the person typically moves back into a lighter stage, and the cycle repeats itself throughout the night
- When an individual is experimentally deprived of REM sleep, certain emotional states become predominant. The subjects show greater anxiety and irritability When a normal subject is experimentally deprived of non-REM sleep for several nights, he or she will often begin to complain of musculoskeletal tenderness, aching, and stiffness
- pain was produced in subjects’ jaw muscles after 20 to 60 s of voluntary clenching
- This is a significant amount of force, since the maximal clench far exceeds the normal forces used during mastication or any other functional activity
- the condyles are translated far from a stable position Parafunctional activity, by contrast, often results in sustained muscle contraction over long periods. This type of isometric activity inhibits normal blood flow within the muscle tissues. As a result there is an increase in metabolic by-products within the muscle tissues, creating the symptoms of fatigue, pain, and spasms less influence over muscle activity
- it is important to remember that occlusal factors are certainly not the only etiologic factors that can contribute to TMD Orthopedic instability is the critical factor that must be considered in assessing relative risk factors for TMD. Also, a small discrepancy of 1 to 3 mm is epidemiologically normal and not apparently a risk factor. Small discrepancies appear to be well within the individual’s adaptability. Shifts of greater than 3 to 4 mm present more significant risk factors for TMD
- parafunctional activities were actually provoked by certain tooth contacts As an occlusal interference becomes chronic, the muscle response is altered. A chronic occlusal interference may affect functional activity in one of two ways. The most common is to alter muscle engrams so as to avoid the potentially damaging contact and get on with the task of function.