MUSCLES OF MASTICATION

Dr. Arif IsmailDept. Of orthodontics

CONTENTS

• Introduction• Development • Anatomy• ACTIONS• Innervation & Vasculature• Clinical Significance & Applied

Aspects• Conclusion

INTRODUCTION

Traditionally four powerful muscles – Masseter, Temporalis, Medial Pterygoid & Lateral pterygoid are called the “Muscles

of Mastication”

Accessory MusclesSuprahyoid muscles• Mylohyoid• Geniohyoid• Stylohyoid• DigastricInfrahyoid Muscles• Sternothyroid• Omohyoid• Thyrohyoid• Sternohyoid

DEVELOPMENT

Muscles of mastication develops from the mesoderm of the first brachial

arch that is also called the Mandibular Arch

Pterygoid Muscle• Differentiate in the 7th week• It is related to the cartilage of the cranial

base and the condyle initially• Later as the bony skull appears and

increases in width and length, the muscle expands rapidly

Temporalis muscle• Begins lateral development in the 8th

week, occupying the space anterior to the otic capsule

• As the temporal bone begins to ossify in the 13th week, the muscle attaches to it

Masseter muscle• Begins attachment to the zygomatic arch

as it undergoes lateral growth, providing space for muscle development

UPPER HEADOrigin-infratemporal surface & crest of greater

wing of sphenoid

LATERAL PTERYGOID

Lower headOrigin- lateral surface of the lateral pterygoid

plate

ACTIONSuperior Head• active during the power stroke.Power stroke refers to

movement that involves closure of the mandible against resistent such as in chewing or clenching the teeth together.

Inferior Head• Depression(bilateral): depresses the mandible along

with suprahyoid and infrahyoid muscles to open the mouth

• Protrusion(bilateral): the lateral pterygoid acting together are the prime protractors of the mandible.

• Contralateral excursion(unilateral): the medial and lateral pterygoid muscle of the two sides contact alternately to produce side to side movement of the mandible(as in chewing

Nerve SupplyThe nerve to the lateral pterygoid muscle branches off from the masseteric or buccal nerve, which is the branch of the anterior trunk of the mandibular nerve

Blood SupplyPterygoid vessels from Maxillary artery

Superficial headMaxillary tuberosity & pyramidal process of palatine bone

Deep HeadMedial surface of the Lateral plate of Pterygoid process and

Pyramidal process of Palatine bone

ACTION• Elevation (bilateral) : The medial pterygoid acting

along with the masseter muscle are powerful elevators of the mandible

• Protrusion( bilateral): The insertion of the muscle is posterior to its origin and therefore it helps in protrusion of mandible

• Contralateral excursion: The medial and lateral pterygoid muscle of two sides contract alternately to produce Side-to-Side movement of Mandible

Nerve SupplyThe never supplying the medial pterygoid muscles is the medial pterygoid nerve branch of the mandibular nerve

Blood SupplyThe artery supplying the medial pterygoid muscles is a branch of the maxillary artery

ORIGINFloor of temporal fossa(inferior temporal line)Overlying temporal fascia of the side of skull

TEMPORALIS

InsertionMargins & deep surface of coronoid process

Anterior Border of Ramus

ActionIt can be divided into 3 distinct areas according to fiber direction and function • The Anterior fibers are directed almost vertically-

elevation of mandible

• The middle fibers run obliquely forward as they pass downward -elevate and retrude the mandible

• The posterior fibers are aligned almost horizontally - retrusion of mandible

Nerve SupplyDeep temporal branches of the anterior trunk of the mandibular nerve

Blood SupplyThis is furnished by the middle & deep temporal arteries. The middle temporal artery is a branch of the superficial temporal artery & the deep temporal arteries are branches of the maxillary artery

Superficial LayerIt is the largest component that arises from the anterior twothirds of the lower border of the zygomaticarch

Masseter

Middle LayerThe middle layer takes its orgin from the medial surface of the

anterior twothirds and the lower border of posterior one third of the arch

Deep LayerThe deep layer arises from the whole length of medial

surface of the zygomatic arch

Action• Elevation(bilateral):masseter elevates the mandible

to occlude the teeth in mastication.• Ipsilateral excursion(unilateral): as the origin of the

masseter muscle is slightly lateral to its insertion , a single masseter muscle can move the mandible to the same side.

• Retrusion: (bilateral): when the mandible is in a protruded position the deep fibers are in a position to retrude the mandible

Nerve supplySupplied by Masseteric nerve a branch of anterior division of Mandibular nerve

Blood SupplySupplied by masseteric artery branch of maxillary artery

Muscle as an etioogy of malocclusion

Muscle dysfunction

Facial asymmetry in a eleven yr old boy whose masseter muscle was missing on left side

MPDS

• Pain disorder in which unilateral pain is referred from trigger points in myofacial structure

• Constant pain, dull acheLaskin’s Cardinal Signs• Muscle tenderness• Pain• Clicking or propping noise in TMJ• Limited Jaw Movement

Trismus

• Inability to normally open the mouth due to one of the many causes

• Inflammation of muscles of mastication• Pericoronitis• Peritonsillar abscess• Temperomandibular joint Disorder(TMD)• Submucous Fibrosis

Temporal Tendonitis

• Chronic strain from temporalis muscle pulling on tendon that attaches to mandible

• Causes sharp headaches in temple just to side of the eyes

Conclusion

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

• It is crucial responsibility of a clinician to recognize each patient’s muscular environment and be aware of the problems related with excessive or deficient use of muscle and their bearing to the dentition