Download - Muscles of mastication
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