muscles of mastication.pptx

MUSCLES OF MASTICATION & PHYSIOLOGY OF MASTICATION

PRESENTED BY: DR. POOJA BHASALE

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CONTENTS

MASTICATION MASTICATORY SYSTEM MUSCLES OF MASTICATION PHYSIOLOGY OF MASTICATION

APPLIED ANATOMY

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MASTICATION DEFINITION:

The act of chewing accomplished by coordinated activity of tongue, mandible, mandibular musculature and structural components of temporo mandibular joint and controlled by neuromuscular components. (MOSBY MEDICALGLOSSARY 2000)

The objective of mastication is to crush, triturate and mix food with saliva, so that food can be transported by deglutition down the digestive canal.3

MASTICATORY SYSTEM

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MASTICATORY SYSTEM, composes of the Teeth and their investing structures.

The skeletal TMJ, mandible and maxilla. The neuromascular components muscle of mastication and the so-mato sensory system.5

MUSCLES OF MASTICATION

They are functionally classified as: Jaw elevators: Masseter, Temporalis, Medial pterygoid ,Upper head of lateral pterygoid Jaw depressors: Lower head of lateral pterygoid, Anterior digastric ,Geniohyoid Mylohyoid .

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PRIMARY MUSCLES OF MASTICATION: The Masseter The Temporalis The Lateral Pterygoid The Medial Pterygoid SECONDARY MUSCLES OF Digastric Geniohyoid Buccinator Mylohyoid MASTICATION:

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DevelopmentThe muscular system develops from intra embryonic mesoderm. Muscle tissues develop from embryonic cells called myoblast. Muscular component of Branchial arch form many striated muscles in the head and neck region. Muscles of mastication are derived from first brachial arch that is the MANDIBULAR ARCH8

MASSETERORIGIN1.

Superficial layer : Anterior 2/3rd of the lower border of the zygomatic arch and from the zygomatic process of the maxilla. Middle layer : From anterior 2/3rd of the deep surface and posterior 1/3rd of the lower border of the zygomatic arch. Deep layer : From the deep surface of the zygomatic9

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INSERTION :Superficial layer lower part of lateral surface of ramus of mandible Middle layer middle part of ramus

Deep layer upper part of the ramus & coronoid process10

ACTIONS: Elevation of the mandible lateral movements of the mandible for efficient chewing and grinding of the food unilateral chewing Retraction of the mandibleNERVE SUPPLY Massetric Nerve A branch of the anterior division of the mandibular nerve.

VASCULAR SUPPLY Massetric branch of maxillary artery. Facial artery. Transverse facial branch of superficial facial artery.

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Clinical Importance of Masseter Muscle of Mastication

Masseter muscle can be palpated both intraorally and extraorally.Most common muscle involved in Myositis Ossificans. The muscle that commonly undergoes Hypertrophy in Bruxism is Masseter Because of the Multipennate arrangement of fibers masseter is a very powerful muscle.12

THE TEMPORALIS

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ORIGINTemporal fossa , excluding the zygomatic bone. Temporal fascia (Fascia arising from the superior temporal line)

INSERTION

The margins and the deep surface of the coronoid process.

The anterior border of the ramus of the mandible.

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NERVE SUPPLY

Deep temporal branches from the anterior division of the mandibular nerve

VASCULAR SUPPLY

Deep temporal branches from the second part of maxillary artery

ACTIONS

Elevates the mandible.

Side to side grinding movements.Retracts the mandible

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LATERAL PTERYGOIDORIGIN: Upper head- from the infratemporal surface and crest of greater wing of sphenoid bone. Lower head: from the lateral surface of the lateral pterygoid plate. INSERTION Pterygoid fovea on the surface of the neck of the mandible.(upper head insertion) Ant. Margin of the articular disk of of the capsule of the TMJ.16

VASCULAR SUPPLY

Pterygoid branches of maxillary artery. NERVE SUPPLY

A branch from the anterior division of the mandibular nerve.

ACTIONS

Depresses the mandible to open the mouth. Lateral and medial pterygoid protrude mandible.

Turn the chin to left side as part of grinding movements.Translation of the condylar head onto the articular eminence is produced by contraction of the lateral pterygoid17

MEDIAL PTERYGOID

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MEDIAL PTERYGOID

ORIGIN Superficial head : from the tuberosity of maxilla and adjoining bone. Deep head from the medial surface of the lateral pterygoid plate and the adjoining part of the palatine bone. INSERTION Insertion is seen on the Medial angle of the Mandible

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VASCULAR SUPPLY

Pterygoid branches of maxillary arteryNERVE SUPPLY

Nerve to the medial pterygoid, which is a branch of the main trunk of the mandibular nerveACTIONS

Elevates mandible. Helps protrude mandible Right medial pterygoid and lateral pterygoid cause left lateral excursion of mandible.20

Clinical Importance of Medial Pterygoid Muscle:

Medial Pterygoid muscle can be palpated only intraorallyMost commonly involved in MPDS. Trismus following inferior alveolar nerve block is mostly due to involvement of medial pterygoid muscle

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MANDIBULAR MASTICATORY MOVEMENT The range of mandibular masticatory movements were first described by Ulrich and Bennet. The movement about the horizontal axis, which occurs in the Saggital plane can be demonstrated when the retruded mandible produces purely rotational opening and closing

movements around the hinge axis which extends throughboth the condyles,

The movement along the vertical axis which occurs the horizontal plane, can be demonstrated when the mandible moves in the lateral excursion. The movement about the sagittal axis, occurs when the mandible moves to one side and cause the condyle on the

contralateral side travels forward

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CHEWING CYCLEThe chewing cycle comprises of 3 phases: 1. Opening phase. 2. Closing phase. 3. Occlusal phase.

REF: APPLIED ORAL PHYSIOLOGY 2ND EDITION (C.L.B. LAVELLE)

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OPENING PHASEDuring opening phase the masticatory muscles undergo isotonic contraction or relaxation.During this phase the temporalis and the pterygoid muscles are active. There is usually a lateral mandibular shift to the working/functional side.REF: APPLIED ORAL PHYSIOLOGY 2ND EDITION (C.L.B. LAVELLE)

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CLOSING PHASE

During the closing phase of mastication the temporalis muscle on the working side is first to become active followed by both masseters and temporalis of the balancing side. Tooth contact glides may occur as the opposing teeth contact one another during the terminal phase of closing.REF: APPLIED ORAL PHYSIOLOGY 2ND EDITION (C.L.B. LAVELLE)25

OCCLUSAL PHASE

In this phase the elevator muscular contraction is strictly isometric only when the teeth are in contact or when there is a hard unyielding object in between them. Each chewing cycle has duration of about 700 ms and tooth contact of about 200 ms. In the intercuspal position the jaw is stationary for approxiamately 100ms before next cycle begins.


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TOOTH CONTACT

A maximum force of about 50kg can be developed between the molar teeth of a dentate patient although forces of upto 150kg have been recoded between the molar teeth in eskimos.


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OCCLUSAL RELATIONS AND MASTICATIONStudy done by: Samuel Adam and Helmut Zander Three test food was used, bread, lettuce and peanut, in analyzing the functional tooth contact in four adults. The frequency of contact was least in the early phase of mastication, increased in the middle third of mastication and was greatest during the last part for both the intercuspal position and lateral position.28

Another study was done by Henry Beyron on the Australian aborigines. The purpose of this investigations is to obtain information on occlusion and mandibular function concerning the anatomic size and shape of the dental arch, the intercuspal position, occlusal contacts and the mandibular movements and its shape and size during mastication- Envelope movement The study concluded, the envelope movement of mastication was registered during chewing, began on one side with 2.3.and 4 cycles, then move on the other side after an opening movement . The means for the vertical dimension of the masticatory cycle were: 18mm- young 17 mm middle age 15mm- old age

Showed that there is loss of vertical dimensions as one ages.29

PHYSIOLOGY OF MASTICATIONMastication Involves

1. Contraction of muscles that control the a. mandible b. tongue c. cheeks and lips2. Afferent (sensory) feedback from oral structures

3. Brainstem reflexes4. Central generation of the appropriate pattern of muscle excitation

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Unique features of Masticatory MusclesHave shorter contraction times than most other body muscles. Incorporate more of muscle spindles to monitor their activity. Do not have golgi tendon organs to monitor tension. Elevators predominantly white fibres which perform fast twitching. Do not get fatigued easily. Psychological stress increases the activity of jaw closing muscles. Occlusal interferences cause a hypertonic synchronous muscle activity. Closing movement also determined by the height of the teeth.31

NEURAL MASTICATORY RECEPTORS

Muscle spindles.Golgi tendon organs.

Periodontal mechanoreceptors.Mucus membrane receptors. Joint receptors.


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MUSCLE SPINDLES

Mandibular elevators have large number of spindles where as the digastric ,facial and lateral pterygoid muscle are few.33

GOLGI TENDON ORGAN

There is no evidence of such units within the masticatory muscles or tension receptor afferents in the trigeminal ganglion.


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1. 2. 3. 4. 5. 6. 7.8.

The periodontal ligament contains mechanoreceptors that respond to the forces applied to the teeth. These mechanoreceptors have a wide range of properties: Some are excited by just a few microns of tooth displacement. Some are less sensitive and respond only to much larger forces. Some exhibit directional sensitivity. Some are slowly adapting and produce continuous discharge when a constant stimulus is applied. Some adapt more rapidly producing only a few impulses immediately when stimulated. Some are rapidly adapting units. Some are very slowly adapting units and provide a constant discharge that can be increased or decreased.The conduction velocities of the periodontal membrane menachanorecptor fibers range from 25-80m/s

PERIODONTAL MECHANORECEPTORS


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MUCOUS MEMBRANE RECEPTORS

There are some cells in the mesencephalic nucleus, main sensory and spinal trigeminal nuclei that respond to pressure in the palate, particularly in the region just distal to the central incisors.

REF: APPLIED ORAL PHYSIOLOGY 2ND EDITION (C.L.B. LAVELLE)36

JOINT RECEPTORSFree nerve fibres comprise the predominant receptors in the TMJ capsule These appear to be on the lateral aspect of the joint capsule and lateral ligament and supplied by a branch of the auriculotemporal nerve These fibers are small in diameter (upto 2 m).37

JAW REFLEXES

Jaw closing reflex. Jaw opening reflex. Tooth contact reflexes. Jaw unloading reflex. Horizontal jaw reflex.


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The existence of jaw reflexes ( jaw jerks , jaw opening and jaw closing ) suggest that neural connections could provide the following: 1. Length servo mechanisms for jaw movement control.Positive feedback mechanisms to reinforce muscular contraction forces when teeth contact a bolus. Protective mechanisms which limit the maximum forces developed on the teeth and mucus membranes.

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3.

4.

REF: APPLIED ORAL PHYSIOLOGY 2ND EDITION (C.L.B. LAVELLE39

The coordination and rhythmicity of mastication has been attributed to the alternate activation of two simple brain stem reflexes. These are the jaw opening reflex, activated by tooth pressure or tactile stimulation of wide areas of the mouth and lips, and the jaw-closing reflex, which follows stretching of the elevator muscles during opening.Stomatologija, Baltic Dental and Maxillofacial Journal, 2005, Vol. 7., N. 3.

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JAW JERK REFLEX

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JAW JERK REFLEXSimple jaw closing reflex has a 6ms latency period between stimulus and movement. The monosynaptic reflex involves stretch induced masseter/ temporalis muscle spindle activation Similar to knee jerk reflex This reflex is thought to relate to the fine control of jaw movements to take into account different consistencies of food. (Mckay G, Yemm R, Cadden Br Dent J 1992)

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JAW OPENING REFLEX

The jaw opening reflex is a response to orofacial stimuli and involves two or more synapses and excitation of the motor neurons that supply the digastric and the inferior head of the lateral pterygoid muscles. The interneurons, relaying the sensory afferents from the orofacial region to the digastric motor neurons. These are located in the trigeminal spinal tract nucleus and adjacent reticular formation. The trigeminal spinal tract nucleus also relays afferent input from the face, oral mucosa, teeth and TMJ to the motor neurons This reflex is thought to help prevent injury when biting or chewing objects that may cause damage. 43

TOOTH CONTACT REFLEX

Reflex changes that occur in the elevator muscles when the upper & lower teeth are snapped together. There is transient activation followed by a silent period & then a phase of increased & decreased activity in the elevators A silent period may comprise a frequent occurrence in normal masticatory tooth contacts reflecting periodontal mechanoreceptor activity, although muscle spindle may also be involved.

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JAW UNLOADING REFLEX

When the jaw is suddenly unloaded(eg. Cracking a nut), a protective reflex limits further jaw closing muscular activity. This sudden reduction is associated with reflex excitement of the jaw depressor muscles.


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HORIZONTAL JAW REFLEXES

Lateral, protrusive and retrusive reflex mandibular reflexes are important in finely controlled masticatory mandibular movements.


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CENTRAL PATTERN GENERATORCentral Pattern Generator: Group of neurons in the CNS which can automatically execute a complex motor act either spontaneously (e.g. respiration) or other stimulus (e.g. swallowing, walking). without additional conscious input. General Theory: Mastication excitation is due to a brain stem Central Pattern Generator (CPG) that spontaneously stimulates jaw openers and jaw closers in sequence. Once an efficient chewing pattern is found, it is learned and repeated. This learned pattern is called a muscle engram.47

APPLIED ANATOMY

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Direction of muscle pull on the depressors: the anterior belly of the diagastric muscle the pterygoid muscle and to a lesser degree the mylohyoid muscle function as mandibular depressors and retractors in the fractured mandible, these muscles pull the fragments downward, medially and posteriorly50

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Masseter muscle and direction of pull on malar eminence : The masster muscle is short, strong muscle that elevates the mandible. It tends to distract the malar eminence inferiorly and medially after a trimalar fracture .53

TEMPORAL TENDONITISTemporal Tendonitis, "The Migraine Mimic A very common headache disorder. Whiplash injuries from auto accidents. Jaw joint hurts and aches; jaw opening may be restricted due to painful tendon not stretching freely. Temple aches and hurts (temple headache) with pain radiating over the ear to the back of the head and into the neck.54

TEMPORAL TENDONITISPain Reference Sites of Temporal TendinitisPain at TM Joint. 2. Ear pain, stuffiness in ear 3. Retro-orbital pain sometimes radiating to occiput and shoulder 4. Upper and lower molar teeth ache 5. Pain at or near the eye 6. Lateral temple1.

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MASSETER HYPERTROPHY

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MASSETER HYPERTROPHYMasseter hypertrophy is usually an asymptomatic enlargement of one or both masseter muscles. Majority of cases, etiology is idiopathic. Numerous factors such as malocclusion, bruxism, clenching, or temporomandibular joint disorders, have been cited. Muscle function may also be impaired, thus causing conditions such as trismus, protrusion, and bruxism57

TEMPORAL MUSCLE HYPERTROPHY

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TEMPORAL MUSCLE HYPERTROPHYTemporalis muscle hypertrophy is rare and may present unilaterally or bilaterally. Variable combinations with masseteric hypertrophy are also reported. It may be associated with a parafunctional habit or occur as an idiopathic entity.59

BRUXISM

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BRUXISM(Tooth grinding,Occlusal Neurosis)A habit of grinding, clenching, or clamping the teeth. The force so generated may damage both tooth and attachment apparatus. (Glossary of Periodontal Terms 4thedition)

Bruxism often occurs during deep sleep or while under stress. In some circumstances, nightime grinding and clenching can wear down tooth enamel, increase temperature sensitivity, and cause severe facial pain and jaw problems, such as temporomandibular joint disease (TMJ). Bruxomania is similar to but occurs when a person is awake.61

TRISMUS

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MASTICATORY MUSCLES PAIN

Myofascial Pain Myositis Myospasm Local Myalgia Myofibrotic Contracture Protective Muscle Splinting

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MYOFACIAL PAINETIOLOGY

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MYOFACIAL PAIN

When the nerve that is connected to the muscle becomes irritated small nodules or contractures form causing the muscle to become tight and painful. These contractures are called trigger points. Trigger points will often refer pain into distant

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MYOSITISArises from direct trauma or infection close to the muscle. Associated pain increases with mandibular movement, thereby limited range of motion .

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MYALGIAPain in localised area of one masticatory muscle( usually masster or temporalis) May result from ischemia or fatigue. May present as delayed-onset muscle soreness and protective cocontraction Fatigue while chewing Tender muscles upon mastication.68

MYOFIBROTIC CONTRACTURE

Extended period of limited range of mandibular movement results in fibrosis of the muscle and related attachments, creating painless condition callled myofibrotic contracture.

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PROTECTIVE MUSCLE SPLINTINGIt is the rigidity of the muscle occuring as a means of avoiding pain caused by movement of a part. It is a protective reflex mechanism May act as a proctective mechanism in conditions such as toothache,trauma and effect of local anesthetics.

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MYOSITIS OSSIFICANS

This is a benign conditon which results in reactive heterotopic bone formation, usually producing limitation of opening of the jaws. CLINICAL FEATURES: Limited mouth opening(trismus) TYPES: MYOSITIS OSSIFICANS TRAUMATICA MYOSITIS OSSIFICANS PROGRESSIVA M O ASSOCIATED WITH PARAPLEGIA M O ASSOCIATED WITH POLIOMYELITIS ETIOPATHOLOGY: Trauma leads to intramuscular hemmorhage which results in reactive heterotrophic bone formation within the muscle.71

Impaired Masticatory Behavior in Subjects With Reduced Periodontal Tissue SupportAnders S. Johansson,* Krister G. Svensson,* and Mats Trulsson* Background: Mechanoreceptors situated in the periodontal ligament provide detailed information about intensive and spatial aspects of tooth loads, which support the neural control of masticatory forces. We asked whether a reduced periodontal ligament due to periodontitis, and, thus, an altered mechanoreceptive innervation of the teeth, would affect masticatory behavior when subjects used incisors to hold and split food. Methods: We tested 11 subjects with reduced periodontal tissue support that rendered 30% to 70% alveolar bone loss for at least one pair of opposing anterior incisors. Forces were recorded when subjects used their affected incisors to hold half of a peanut for 4 seconds and then split it. Age- and gender-matched healthy subjects served as the control group. None of the participants showed acute oral symptoms or massive periodontal inflammation. Results: The test group used greater force when holding food between the teeth (1.1 0.4 N [ mean 1 SD]) compared to the control group (0.4 0.2 N). Hold forces used by subjects in the test group were also more variable, both within and between trials. The increase in bite force applied to split the peanut was slower and more hesitant for subjects in the test group compared to the control group.

Conclusions: Reduced periodontal tissue support accompanies impaired regulation of masticatory forces. Faulty mechanoreceptive innervation of the periodontal ligament explains the elevated hold force, whereas a change in biting strategy due to the weakened support of the teeth may account for the more defensive food-splitting behavior.

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Correlation between periodontal status and biting force in patients with chronic periodontitis during the maintenance phase of therapyNoriko Takeuchi,

Tatsuo Yamamoto Article first published online: 7 JAN 2008

Aim: The association between periodontal status and biting force is unclear. The aim of this study was to investigate the relation between periodontal status and biting force in patients with chronic periodontitis during the maintenance phase of periodontal treatment. Material and Methods: A total of 198 patients, who had entered a periodontal maintenance programme, were examined for the presence of restorations on the occlusal surface, probing pocket depth, clinical attachment loss (CAL), bleeding on probing, and mobility of teeth. Quantitative analysis of total biting force, occlusal contact area and biting pressure (defined by biting force per 1 mm2 of occlusal contact area) was performed using microcapsular pressure-sensitive sheets. Results: A multiple stepwise regression analysis showed that total biting force and occlusal contact area were positively associated with the number of present teeth and negatively associated with female gender, mean CAL and mean probing pocket depth. Biting pressure was positively associated with CAL.

Conclusions: Reduced periodontal support was found to be associated with decreased total biting force and with increased biting pressure (defined as force per 1 mm2 of occlusal contact area).73

CONCLUSION

Mastication is oral motor behavior reflecting central nervous system commands, and many peripheral sensory inputs to modulate the rhythmic jaw movements. 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 new made restorations.

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REFERENCESGRAYS ANATOMY HUMAN ANATOMY BY B.D. CHAURASIA. VOL. III GUYTONS TEXT BOOK OF PHYSIOLOGY. APPLIED ORAL PHYSIOLOGY 2ND EDITION(C.L.B. LAVELLE)

BURKETS ORAL MEDICINE DIAGNOSIS AND TREATMENT (TENTH EDITION)75

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