Muscles of Mastication

• The lecture has been created so that dental students can understand the muscles of mastication, their function, and why they are important in dentistry
• At the end of this lecture, you should be able to list the muscles of mastication and describe their origin, insertion, action, innervation, and blood supply

What are the muscles of mastication?

• Muscles of mastication connect to the mandible, facilitating movement for chewing and grinding
• These muscles allow the mandible to move in five main ways: forwards (protrusion), backwards (retraction), up/close (elevation), down/open (depression), and side-to-side (rotation)

Why is it important to understand these muscles?

• Knowing these muscles is important for understanding the impact of ID blocks, pain during mastication, trismus, and clenching or grinding

Masseter

• A thick, quadrilateral muscle comprised of two parts: superficial and deep

Masseter Superficial Part

• Origin: arises from the anterior two-thirds of the lower border of the zygomatic arch
• Insertion: fibres pass downwards and backwards to be inserted on the outer surface of the ramus of the mandible

Masseter Deep Part

• Origin: arises from the posterior third of the lower border and the entire medial surface of the zygomatic arch
• Insertion: fibres pass downwards and backwards to be inserted on the ramus above the angle of the mandible (superior to the superficial part)
• Action: fibres contract to close the mouth/elevate the mandible
• Nerve supply: masseteric nerve (anterior division of the mandibular nerve)
• Blood supply: facial branch of the superficial temporal artery and the masseteric branch of the maxillary artery

Temporalis

• A fan-shaped muscle located on either side of the head
• Origin: fibres arise from the temporal fossa, bound at the top by the inferior temporal line
• Fibres converge and descend into a tendon passing through the zygomatic arch to the side of the head
• Insertion: the top and medial surface of the coronoid process and the anterior border of the ramus of the mandible
• Action: anterior fibres elevate the mandible; posterior fibres elevate the mandible and retract the head of the condyle back into the glenoid fossa
• Nerve supply: anterior and posterior deep temporal nerves (anterior division of the mandibular nerve)
• Blood supply: middle temporal branch of the superficial temporal artery and deep temporal branches of the maxillary artery

Lateral Pterygoid

• A short, thick, triangular muscle arising from two heads: upper and lower

Lateral Pterygoid Upper Head

• Origin: infratemporal surface and crest of the greater wing of the sphenoid bone

Lateral Pterygoid Lower Head

• Origin: lateral surface of the lateral pterygoid plate of the sphenoid bone
• Insertion: fibres merge and insert into the pterygoid fovea on the anterior aspect of the neck of the mandible; some fibres may insert with structures of the TMJ
• Action: bilateral contraction opens and protrudes the mouth; unilateral action produces grinding or side-to-side movement
• Nerve supply: lateral pterygoid nerve (anterior branch of the mandibular nerve)
• Blood supply: pterygoid branches of the maxillary artery

Medial Pterygoid

• A thick, quadrilateral muscle arising from two heads: deep and superficial

Medial Pterygoid Large Deep Head

• Origin: medial surface of the lateral pterygoid plate of the sphenoid bone

Medial Pterygoid Small Superficial Head

• Origin: tuberosity of the maxilla and pyramidal process of the palatine bone
• Insertion: fibres pass downwards, backwards, and laterally to be inserted into the medial surface of the ramus and angle of the mandible, below and behind the inferior dental foramen
• Action: elevates the mandible and, with the lateral pterygoid muscle, protrudes the mandible
• Nerve supply: medial pterygoid branch of the mandibular nerve
• Blood supply: pterygoid branches of the maxillary artery

Digastric

• Has an anterior and posterior belly

Digastric Anterior Belly

• Origin: arises from the digastric fossa on the lower border of the mandible
• Nerve supply: mylohyoid nerve
• Blood supply: submental branch of the facial artery

Digastric Posterior Belly

• Origin: arises from the digastric notch on the mastoid process of the temporal bone
• Insertion: meets above the hyoid bone at the intermediate tendon, held by a fibrous sling
• Nerve supply: digastric branch of the facial nerve VII
• Blood supply: posterior auricular/occipital artery
• Action: depression of the mandible and elevates the hyoid bone during chewing and swallowing

Buccinator

• Forms the cheek
• Origin: pterygomandibular raphae and buccal alveolar bone (in maxillary and mandibular molars regions)
• Insertion: fibres run horizontally, blending with the Orbicularis Oris at the corners of the mouth
• Action: pulls the corner of the mouth back, compresses the cheek against the buccal surfaces of molars, and regulates the vestibular region with the tongue
• Nerve supply: facial nerve, buccal branch
• Blood supply: facial and maxillary arteries

Geniohyoid

• A narrow muscle situated above the medial part of the mylohyoid line
• Origin: arises from the inferior genial tubercle
• Insertion: fibres run downwards and backwards into the body of the hyoid bone
• Action: aids in deglutition and opening the mouth by depressing the mandible
• Nerve supply: hypoglossal nerve
• Blood supply: sublingual branch of the lingual artery

Genioglossus

• Origin: arises from the superior genial tubercle on the inner surface of the mandible
• Insertion: enters the dorsum of the tongue, forming a fan-shaped muscle, with superior fibres going to the tip of the tongue and inferior fibres to the body of the hyoid bone
• Action: depresses the tongue, retracts it with inferior fibres, and protrudes it with superior fibres
• Nerve supply: hypoglossal nerve
• Blood supply: sublingual branch of the lingual artery and submental branch of the facial artery