Seminar 2 Stomatognathic System

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The stomatognathic systemPart -1

10/22/2012Dr. Akshi S GvalaniP.G. Dept. of ProsthodonticsTerna Dental College, Nerul, Navi Mumbai

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The stomatognathic system

System: a set or series of interconnected or interdependent parts or entities (objects, organs, or organisms) that act together in a common purpose or produce results impossible by action of one alone.

A biological system (or organ system or body system) is a group of organs that work together to perform a certain task


The combination of organs, structures, and nerves involved in speech, mastication, and deglutition of food. This system is composed of the teeth, the jaws, the masticatory muscles, the tongue, the lips, the surrounding tissues, and the nerves that control these structures.

Mosby's Medical Dictionary, 8th edition. © 2009, Elsevier.

BASIC MUSCLES:

Temporalis

Masseter

Medial pterygoid

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joint

muscles

teeth


Lateral pterygoid

Jaw elevators

Masseter

Temporalis

Medial pterygoid

Jaw depressors

Lateral pterygoid

Anterior digastric

Geniohyoid

Mylohyoid

Masticatory muscles

Anatomically the muscles of mastication can be divided into simple and complex muscles (Hannam 1994, 1997).

The lateral pterygoid and the digastric muscles are counted among the simple muscles.

In contrast, the complex muscles include the temporal, masseter, and medial pterygoid muscles with their many aponeuroses and varying sizes

Embryology

The basic muscles of mastication develop from the mesoderm of the first pharyngeal arch.

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Innervation

So they receive all their innervations from the mandibular branch of the trigeminal nerve, all from the anterior division except the medial pterygoid which gets its nerve supply from the main trunk.

Temporal muscle

ORIGIN

The temporal fossa on the lateral aspect of the skull and adjoining temporal fascia, bounded above by temporal line and below by the zygomatic arch.

Anterior fibers – downward

Posterior fibers – forward tendon

Intermediate fibers – obliquely

INSERTION

Coronoid process of the mandible and the anterior border of the ramus.

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INNERVATION AND ARTERIAL SUPPLY

ACTION

Three functional parts can be distinguished.

The anterior part has muscle fibers that pull upward and serve as elevators.

The middle part effects closure of the jaws and, with a posterior vector, retrusion

According to DuBrul (1980) the posterior part is involved primarily with jaw closure and only to a minimal extent with retrusion

During normal opening and closing movements,

During chewing

Working side balancing side

PALPATION

A healthy muscle does not elicit sensations of pain or tenderness when palpated.

Usually accomplished with the palmar surface of the middle finger

A single firm thrust of 1 to 2 seconds duration

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Specific palpation is usually accomplished by laying the palpating finger parallel with the muscle fibers to be tested.

The actual palpating movements then take place at right angles to the direction of the fibers. In this way even lesions in different layers of a muscle, such as the pars profunda and pars superficialis of the masseter, can be reliably differentiated

A force of approximately 40 N/cm2 should be used during specific palpation

DEGREES OF MUSCLE TENDERNESS

0 - no pain or tenderness

1 – palpation is uncomfortable

2 – definite discomfort or pain

3 – evasive action or verbal desire to not palpate the area

Palpating the lateral aspect of the tendon of the temporal muscle

1 o'clock position.

Little finger or the middle finger, tip of the coronoid process or the lateral side of the retromolar triangle may be selected as the starting point.

Palpation of the medial aspect of the temporal tendon

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The little finger of the right hand is used with the examiner in the 11 or 12 o'clock position

The anterior region is palpated above the zygomatic arch and anterior to the TMJ

The middle region is palpated directly above the TMJ and superior to the zygomatic arch

The posterior region is palpated above and behind the ear.

If uncertainty arises regarding the proper finger placement. The patient is asked to clench the teeth together so that the temporal muscle contracts and the fibers should be felt beneath the finger tips.

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CLINICAL IMPORTANCE

Recording coronoid process area

The patient is instructed to close and move his mandible from side to side and then immediately asked to open wide.

The side to side motion records the activity of the coronoid process in a closed position whereas opening causes the coronoid to sweep past the denture periphery

Content of retromolar pad

Masseter

ORIGIN

Anterior fibers - zygomatic process of maxilla

Superficial fibers – anterior 2/3 of the lower border of the zygomatic arch

Deeper fibers - deeper surface and posterior 1/3 of the lower border

INSERTION

Lateral surface of the ramus and angle of the mandible

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ACTION

The masseter elevates the mandible to cause closing of the mouth

Anterior fibers help in protraction of the mandible

When mandible is protruded the deep fibers stabilize the condyle against the articular eminence

PALPATION

The muscle is palpated bilaterally moving from the zygomatic arch downwards to the inferior border of the ramus .The patient is asked to clench their teeth.

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CLINICAL IMPORTANCE

An active masseter muscle will create a concavity in the outline of the distobuccal border and a less active muscle may result in a convex border. In this area the buccal flange must converge medially .The muscle fibers in that area are vertical and oblique.

Effect of masseter muscle on the distobuccal border

A Moderate activity will create a straight line

B. An active muscle will create a concavity.

C An inactive muscle will create a convexity

Instruct the patient to open wide and then to close against the resting force of your fingers It causes masseter muscle to contract and push against the medially situated buccinator muscle

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Lateral pterygoid

ORIGIN

Upper head - infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone

Lower head - lateral surface of the pterygoid plate

INSERTION

Pterygoid fovea on the anterior aspect of the neck of the mandible

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Intraarticular disc and capsule of the TMJ


ACTION

Inferior head -

1. Unilateral contraction causes a mediotrusive movement of the condyle thus the mandible moves laterally

2. Bilateral contraction leads to mandibular protrusion

3. Along with the mandibular depressors it causes condyle to slide downwards along articular eminence and mouth opens

Superior head – inactive during opening of the mouth

Works in conjunction with the elevator muscles in the power stroke.

FUNCTIONAL MANIPULATION

The patient is asked to protrude the mandible against resistance and Clench on maximum intercuspation The muscle contracts and stretches on clenching.

In order to differentiate pain arising from elevator muscle, the patient is asked to open the jaw wide.

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CLINICAL IMPORTANCE

Unilateral failure of lateral pterygoid muscle to contract results in deviation of the mandible toward the affected side on opening.

Bilateral failure results in limited opening, loss of protrusion and loss of full lateral deviation.

The insertion of the lateral pterygoid in the articular disc occurs in the medial aspect of the anterior border of the disc and thus it plays a role in the TM.J diseases especially internal derangement.

Some of the TM.J. diseases have been due to an attributed variation of the function and attachment of the superior head as an etiological factor in TM.J.diseases.

Medial pterygoid

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ORIGIN

Deep head - Medial surface of the lateral pterygoid plate

Superficial head - Adjoining part of the pyramidal process of the palatine bone and maxillary tuberosity

INSERTION

Medial surface of angle of the mandible

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ACTION

The pull of the muscle is opposite to the direction of its fibers

Fibers of the lateral pterygoid run backwards and laterally

Fibers of the medial pterygoid pass downwards backwards and laterally

Both muscles together protract the mandible

Both pterygoids of one side move one mandibular condyle forwards

Therefore chin moves forward and to the opposite side

FUNCTIONAL MANIPULATION/PALPATION

It can be palpated by placing the finger on the lateral aspect of the pharyngeal wall of the throat, this palpation is difficult and sometimes uncomfortable for the patient

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CLINICAL IMPORTANCE

The medial pterygoid muscle is not usually involved in gnathic dysfunctions but when they are hypertonic, the patient is usually conscious of a feeling of fullness in the throat and an occasionally pain on swallowing

Muscles of the tongue

Extrinsic muscles (associated with functions of mastication deglutition and speech)

Styloglossus

Genioglossus: elevates and protrudes the tongue therefore affects denture in anterior lingual vestibule

Hyoglossus

Palatoglossus

Intrinsic muscles(alter the shape of the tongue)

Transverse

Horizontal

Vertical

Muscles of the face

Buccinator (One who blows the trumpet)

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ORIGIN

C shaped line of origin

1. Outer aspect of maxilla just above the 3 molar teeth

2. Pterygomandibular raphe

3. Outer aspect of mandible just below 3 molar teeth

INSERTION

Fibres run forward and are continuous with the Orbicularis Oris muscle

INNERVATION

ACTION

Aids in mastication by pushing food between the teeth and bringing food to the occlusal table

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Increases air pressure within the mouth as in blowing

CLINICAL IMPORTANCE

The buccal vestibular extent of the mandibular denture is affected mainly by the modiolus and buccinator muscles

The buccal shelf area is intact cortical area and tends not to resorb due to the the constant stimulation of of attachment of buccinator muscle

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The cheek is manually molded in anterior posterior direction using slight finger pressure against the compound or the patient is instructed to control the amount of movement by sucking action.

Orbicularis oris

It has two parts

Intrinsic and extrinsic part.

Intrinsic part is a very thin sheet and originates from superior and inferior incisivus from maxilla & mandible. It inserts into the angle of mouth.

The extrinsic part is actually formed by elevator and depressor muscles of the lips and inserts into the angle of the mouth.

The orbicularis oris FUNCTION IS to compress the lips against the teeth and close the oral orifice

CLINICAL IMPORTANCE

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For mandibular impressions

On recording Labial flange and labial frenum The lip is massaged from side to side to mold the compound to desired functional extension. In order to activate the mentalis muscle the patient is asked to pout or lick his lower lip

For maxillary impressions

In labial flange and labial frenum area.Lift the patients upper lip and vertically place the frenum into the softened compound and mold with your fingers using a side to side external motion

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The modiolus muscle controls the thickness of the denture flange in the mandibular premolar region.

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SUPRAHYOID MUSCLES

Mylohyoid/oral diaphragm

ORIGIN

Mylohyoid line on the medial surface of the body of the mandible.

INSERTION

Most anterior fibers – anterior aspect of the hyoid bone

Remaining fibers – median fibrous raphe

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INNERVATION

ACTION

Helps in deglutition by raising the floor of the mouth

Separates the submandibular and sublingual gland

PALPATION

The mylohyoid muscles can be palpated intraorally while the opposite hand supports the floor of the mouth extraorally.

The index finger of the palpating hand is positioned lateral to the geniohyoid muscle

CLINICAL IMPORTANCE

The middle lingual vestibule is mainly affected by action of the mylohyoid muscle Its intraoral apperance is somewhat misleading

Nagel and Sears have shown that in maximum contraction the fibers are still in the downward and forward direction so that the denture can be extended below the muscle attachment along the mylohyoid ridge

The average mylohyoid border is 4 to 6 mm below the mylohyoid ridge

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Recording the mylohyoid in function

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The tongue movements raise the level of the floor of the mouth through contraction of the mylohyoid muscle. Instruct the patient to place the tip of his tongue into the upper and lower vestibules on the right and left side

Geniohyoid

ORIGIN

Posterior aspect of the symphysis menti below the genioglossus

INSERTION

Anterior aspect of the hyoid bone

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INNERVATION

ACTION

Draws the hyoid bone upwards and forwards

When the hyoid bone is fixed it can depress the mandible

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Anterior belly of the digastric

ORIGIN

Anterior belly - anterior part of base of mandible near midline

Posterior belly – mastoid notch of temporal bone

Intermediate tendon - junction of body and greater cornua of hyoid bone

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PALPATION

Having the patient swallow makes it much easier to locate the muscle at this stage.

Stylohyoid

ORIGIN AND INSERTION

1. Posterior aspect of the styloid process

2. It runs forwards and downwards to end in a tendon that splits to enclose the intermediate tendon of the digastric muscle

3. The tendon is then inserted into the hyoid bone

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Infrahyoid muscles

The origin and insertion of this group of muscles have no particular significance in complete denture prosthodontics

Their action is to fix or depress the hyoid bone so that the suprahyoid muscles can act.

Syllabus of complete dentures Charles Heartwell

Masticatory muscle disorders

Myalgia

Myofascial pain

Myosistis

Splinting and spasm

Contracture

Hypertrophy

Parafunction

Muscle pain

It usually occurs as a result of reflex protective mechanism and myofacial triggers

1. Local muscle soreness2. Muscle splinting pain3. Non -spastic myofacial pains

Referred myofacial pain

The temporal muscle refers only to the temple, orbit and maxillary teeth

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The masseter muscle only to the upper and lower posterior teeth, the ear and the TMJ

The anterior belly of the digastric muscle only to the lower anterior teeth, may radiate to the mastoid region

The medial pterygoid refers pain to the infraauricular and postmandibular area

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The lateral pterygoid muscle refers pain to the TMJ area

Physiologic functions

The three major functions of the masticatory system are

Mastication

Swallowing

Speech

Secondary functions are

Respiration

Expression of emotions

Mastication

The act of chewing food

The time “during which the food is mechanically broken down and mixed with saliva to create a slurry of small particles or bolus that can be easily swallowed” (Lund & Kolta, 2006).

Automatic, practically involuntary

It consists of three phases

Opening phase

Closing phase

Occlusal phase

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Preparatory

Particle reduction

Preswallowing

NEURAL CONTROL

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,

jaw-closing reflex,

Chewing must be learned, and occurs only after tooth eruption.It is possible that periodontal ligament receptors and their stimulation are essential for this learning process

Sensory feedback

epithelial mechanoreceptor afferents,

periodontal afferents,

Temporomandibular joint afferents and muscle afferents

Within the brain-stem is a pool of neurons – central pattern generator (CPG) responsible for the precise timing of activity between synergetic and antagonistic muscles

CHEWING STROKE

The masticatory envelope is usually described as a "tear-drop shape" with a slight displacement at the beginning of the opening phase

Usually the closing phase is lateral to the opening phase although often this relationship is reversed; a reversed masticatory stroke takes place

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The character of the food influences the chewing pattern.

Each chewing cycle has duration of about 700 ms and tooth contact of about 200 ms (1).

EMG ACTIVITY DURING MASTICATION

Ipsilateral inferior head of the lateral pterygoid muscle approximately halfway through the tooth contact period.

Inferior head of the contralateral pterygoid muscle.

These two muscles are active through the entire duration of the opening phase

Digastric muscles

The opening phase ends medial pterygoid muscle contracts

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At the beginning of the closing phase the ipsilateral temporal muscle contracts first, and thereafter the contralateral temporal muscle and both masseter muscles become active simultaneously.

Perioral facial muscles, are active during normal mastication

Electromyographic records taken before the loss of posterior teeth, after the loss of posterior teeth

Deglutition / swallowing

It consists of three phases

Voluntary oral phase

Involuntary pharyngeal phase

Involuntary esophageal phase

ORAL PHASE

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Spoon shaped depression on dorsum contains food bolus

Pharyngeal portion of tongue meets the posterior palate

Lips are apart and teeth do not touch

Tip of tongue is placed on anterior alveolar ridge (anterior alveolar phase)

Posterior seal opens ,lips close and teeth contact

Bolus moves posteriorly on dorsum of tongue toward the fauces

Soft palate elevates and contacts pharyngeal wall to close off the nasopharynx

PHARYNGEAL PHASE

Hyoid is elevated

Respiration is arrested

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Tongue moves posteriorly and superiorly to convey bolus into pharynx

Pharyngeal constrictors move upwards and forwards.

Larynx is raised and pulled under tongue

Epiglottis covers laryngeal aperture and vocal cord contraction also narrows the aperture

Tooth contact stabilizes the mandible while the hyoid and larynx move

Phase ends with the return of soft palate to original position and larynx reopens to restore respiration

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Important muscles in deglutition

MUSCLE ACTION

Buccinator Holds food in contact with teeth

Levator veli palatini ,Tensor veli palatini Raises soft palate

Palatoglossus, styloglossus, hyoglossus. Raises back of tongue during first phase of swallowing

Palatopharyngeus Shuts of nasopharynx during second stage of swallowing

Mylohyoid ,Geniohyoid ,Digastric Elevates tongue and floor of mouth, initiate deglutition

NEURAL CONTROL

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IMMATURE SWALLOW

Alveolar ridges are apart

Tongue protrudes between them

Mandible is stabilized by facial and tongue muscles

DISORDERS IN SWALLOWING

1. Dysphagia – difficulty in swallowing

2. Odynophagia – painful swallowing

3. Aphagia – absence of swallowing due to paralysis of muscles of deglutition or muscle of mastication

4. Abnormal growth on the esophagus (tumor, cancer, outgrowth & overgrowth

Speech

It occurs when a volume of air is forced from the lungs by the diaphragm through the larynx and oral cavity and simultaneous contraction or relaxation of vocal cords.

Occurs during the expiration phase

Form of the mouth determines the exact articulation of sound

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VOICE PRODUCTION

Source of energy – air in the lungs

Vibrators - vocal chords

Resonators /reinforcers –larynx, pharynx, nasal and oral cavity

ARTICULATION

Usually considered to be the joining of parts but in speech it is the movement or approximation of articulators to constrict, impede, or divert the airstream.

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CONCLUSION

The masticatory muscles include a vital part of the orofacial structure and are important both functionally and structurally to the prosthodontist-

1. During functional impression making

2. Accurate recording of various clinical parameters like vertical dimension, centric relation

3. Maintenance of arch form

REFERENCES

Textbook and color atlas of human anatomy

IB Singh

Impressions in complete dentures

Bernard Levin

Complete denture prosthodontics

John J Sharry

Management of TMJ disorders and occlusion

Jeffrey P Okeson

Applied oral physiology

Christopher B Lavelle

Syllabus of complete dentures

Charles Heartwell

TMJ Disorders and Orofacial Pain The Role of Dentistry in a Multidisciplinary Diagnostic Approach

Axel Bumann and Ulrich Lotzmann

Stomatologija, Baltic Dental and Maxillofacial Journal, 2005, Vol. 7. N. 3.

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Seminar 2 Stomatognathic System

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