GOOD MORNING

Muscles ofMastication

Dr Jamshid UsmanPG Prosthodontics

Royal Dental CollegeChalissery,Palakkad

• Introduction• Types• Palpation• Clinical significance• Literature review• Summary• Conclusion

DEFNITIONSGPT 8

• Muscle:• an organ that by contraction producesmovements of an

animal; a tissue composed of contractile cells or fibersthat effect movement of an organ or part of the body.

•  Mastication• is defined as the process of chewing food in preparation

for swallowing and digestion.

• Mastication- four muscles of mastication (or musculi masticatorii) - adduction and lateral motion of the jaw.

• Muscles associated hyoid also responsible for opening the jaw

Primary Muscles Of Mastication

• Temporalis• Masseter• Lateral Pterigoid• Medial pterigoid

Accessory Muscles Of Mastication

• Suprahyoid • Digastric• Stylohyoid• Mylohyoid• Geniohyoid

• Infrahyoid muscles• Sternohyoid• Thyrohyoid• Omohyoid

• Functionally, the muscles of mastication are classified as

• Jaw elevators • Masseter• Temporalis• Medial pterygoid

• Jaw depressors• :Lateral pterygoid• Anterior digastric• Geniohyoid• Mylohyoid

Functionally, the muscles of mastication are classified as

Jaw elevators

• Masseter• Temporalis• Medial pterygoid

Jaw depressors

• Lateral pterygoid• Anterior digastric• Geniohyoid• M ylohyoid

Temporalis Muscle

Temporalis Muscle

• elevation of the mandible.• Large fan shaped.• Origin and Insertion:• From the Parietal bone of the skull and is

inserted on the coronoid process of the mandible.

• Arterial supply:• The Deep Temporal• Nerve Supply:• Deep temporal n

Functions:

• Elevation of the mandible• Retraction of the mandible.• Crushing of food between the molars.• Posterior fibers draw the

mandible backwards after it has been protruded.

• It is also a contribute side to side grinding movement

TemporalisMuscle

Palpation

• To locate the muscle ,have the patient clench.• Apply two pounds of pressure

• 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

•

Clinical Importance of Temporalis Muscle:

• Sudden contraction of temporalis muscle will result in coronoid fracture, which is rare.

• 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

LITERATURE REVIEW

• Antje Tallgren, Dr.Odont, et al. studied jaw muscle activity incomplete denture wearers :A longitudinal ectromyographic study . J ProsthetDent August 1980 Vol44 (2) Pg 123-32

• Tallgren studied the patterns of activity of some masticatory muscles in partially edentulous subjects & fully edentulous.

• The study indicated that loss of posterior teeth causes imbalance in muscular patterns concerning masseter, anterior temporal muscle and digastrics muscle and wearing immediate complete upper and lower dentures revealed inactivity of the jaw closing muscles during the biting actions.

• Bengt ,Ingervall, Dr Odontet al. did an electromyographic study of masticatory and lip function in patient with complete dentures (J ProsthetDent March 1980 Vol43(3) pg 266-71

• T wo groups of patients having new and old dentures were studied.

• The results showed muscle activity during maximal biting was markedly lower in patients with new denture than in patients using the old ones

• No difference in chewing activity was seen with old and new dentures

Masseter muscle

Masseter muscle

• The second most efficient masticatory muscle.

• Multipennate arrangement of fibers• Superficial• Middle• Deep

• The main function of masseter muscle is• Elevation of the mandible• lateral movements of the mandible for

efficient chewing and grinding of the food• unilateral chewing• Retraction of the mandible

• Blood supply:• Masseteric artery .•  • Nerve supply:• Massetric nerve.

Palpation

• The patient is asked to clench their teeth and, using both hands, the practitioner palpates the masseter muscles on both sides extraorally, making sure that the patient continues to clenchduring the procedure.

• Palpate the origin of the masseter bilaterally along the zygomatic arch and continue to palpate down the body of the mandible where the masseter is attached

• Palpate multiple areas of masseter muscle

Clinical Importance of Masseter Muscle of Mastication:

• On Denture border• 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 to avoid displacement due to contraction of the masseter muscle because the muscle fibers in that area are vertical and oblique

Activation of massetric notch and distal areas

• Instruct the patient to open wide and then to close against the resing force of your finger

• Opening wide activates the muscles of pterygomandibularrapheby stretching, whichthereby defines the most distal extension

• Instructing the patient to close against your fingers on the tray handle causes masseter muscle to contract and push against the medially situated buccinator muscle

• .

LITERATURE REVIEW

• According to Garrett NR, Kaurich M et. al a cross- sectional study on Masseter muscle activity in denture wearers with superior and poor masticatory performance was done. JProsthetDent 1995 Dec vol74 (6) 628-36

• The results indicated that application of more equivalent force by the right and left masseter muscles during unilateral chewing is consistent with improved chewing ability indenture wearers

Lateral Pterygoid Muscle:

Lateral Pterygoid Muscle:

• It is divided into 2 heads• Origin:• Upper head – infratemporal surface & crest of

greater wing of sphenoid bone• Lower head – lateral pterygoid plate• Insertion :• Pterygoid fovea on the anterior surface of neck of

mandible• Anterior margin of articular disc & capsule of TMJ

• Nerve Supply:• Pterygoid branch of Trigeminal nerve.• Arterial supply:• Pterygoid branch of Maxillary artery.• Functions:• Depresses the mandible• Protrudes it forward for opening of the jaw• Side Movements

PALPATION OF THE LATERAL PTERYGOID

• Placing the forefinger, or the little finger, over the buccal area of the maxillary third molar region and exerting pressure in a posterior, superior, and medial direction behind the maxillary tuberosity

Clinical Importance of Lateral Pterygoid Muscle:

• Most commonly involved muscle in MPDS• 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

•

LITERATURE REVIEW

• R. Johnstoneand Mc cormick templetonstudied the feasibility of palpating the lateral pterygoid muscle ( JProsthetDent Vol44 (3) Sept 1980 Pg 318-23) and came to a conclusion through dissections and lateral head radiographs that it is not possible to palpate the lateral pterygoidmuscle directly by conventional clinical techniques without applying pressure through the overlying superficial head of medial pterygoid muscle

Medial Pterygoid muscle

Medial Pterygoid muscle:

• It is a thick muscle of mastication.• Origin and Insertion :• It Arises lateral pterygoid plate, and from the

maxillary tuberosity.• Insertion is seen on the Medial angle of the

Mandible

• Arterial supply:• Pterygoid branch of Maxillary artery.• Nerve Supply:• Mandibular nerve through the medial

pterygoid.

• Functions:• Elevates the mandible,• Closes the jaw,• Helps in side to side movement.

Palpation of medial pterigoid

• gently palpate them on the medial aspect of the jaw, • simultaneously from both inside and outside the mouth

Clinical Importance of Medial Pterygoid Muscle:

• Medial Pterygoid muscle can be palpated only intraorally

• Most commonly involved in MPDS• Trismus following inferior alveolar nerve block

is mostly due to involvement of medial pterygoid muscle

LITERATURE REVIEW

• Wodd WW studied the medial pterygoid muscle activity during chewing and clenching. J ProsthetDent.1986 May;Vol 55 ( 5):615-21

• Patterns of medial pterygoidmuscle activity were consistentfor ipsilateralchewing

• Intercuspal clenching initiated less activity when force was directed posteriorly and more activity when directed anteriorly

Accessory muscles

Accessory Muscles Of Mastication

• Suprahyoid • Digastric• Stylohyoid• Mylohyoid• Geniohyoid

• Infrahyoid muscles• Sternohyoid• Thyrohyoid• Omohyoid

Digastric

• Origin anterior belly - digastric fossa (mandible); posterior belly -mastoid process of temporal bone

• Insertion Intermediate tendon (hyoid bone)

• Artery • anterior belly - Submental branch of facial

artery; • Posterior belly -occipital artery• Nerve• anterior belly - mandibular division (V3) of

the trigeminal(CN V) via the mylohyoid nerve; posterior belly - facial nerve (CN VII)

Stylohyoid Muscle

Origin and insertion

MYLOHYOID MUSCLE

• Artery • Mylohyoid branch of inferior alveolar artery • Nerve• mylohyoid nerv e, from inferior alveolar branch of

mandibular nerve• Actions• Raises oral cavity

floor, elevateshyoid, elevates tongue, depressesmandible

GENIOHYOID MUSCLE

• Artery : Facial artery• Nerve : C1 via hypoglossal nerve

• Action: carry hyoid bone and the tongue upward during deglutition

STERNOHYOID MUSCLE

• Artery : Superior Thyroid Artery• Nerve : C1-C3 by a branch of Ansa cervicalis• Action : Depress Hyoid bone

THTROHYOID MUSCLE

• Artery : Superior Thyroid Artery• Nerve : C1 via of Ansa cervicalis• Action : Elevates thyroid Depress Hyoid bone

OMOHYOID MUSCLE

• Artery • Infrahyoid artery from the superior

thyroid artery, suprahyoid branch of the lingual artery.

• Nerve• Ansa cervicalis (C1-C3)• Actions• Depresses the larynx and hyoid bone. Also

carries hyoid bone backward and to the side.

Features of Masticatory muscle

• Have 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 fibrous 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

SUMMARY

Primary Muscles Of Mastication

• Temporalis• Masseter• Lateral Pterigoid• Medial pterigoid

Accessory Muscles Of Mastication

• Suprahyoid • Digastric• Stylohyoid• Mylohyoid• Geniohyoid

• Infrahyoid muscles• Sternohyoid• Thyrohyoid• Omohyoid

CONCLUSION

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

• It can be influenced by a variety of factors many of which are controlled by the practicing prosthodontist

• During functional impression making • Accurate recording of various clinical parameters like

vertical dimension, centric relation • Morphology of artificial tooth • Maintenance of arch form• The proper management and periodical self -

examination of the muscles may provide a greater chance of catching the disease process at an early stage which may be useful for its better prognosis.

REFERENCES

• Human anatomy A K Dutta -#rd Edition• Grays Anaatomy• Burkitsoral medicine diagnosis & treatment 10

th edition• Textbook of Complete dentures by Charles

M Heartwell• Journal Refernces

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