§THE JAW MUSCLES (MASTICATORY MUSCLES) People’s Teacher Prof Hoàng Tử Hùng, DDS, PhD E: tuhung.hoang@gmail.com W: hoangtuhung.com Introduction 1- the jaw muscles are muscles which arise from or insert in the mandible and which act to the movement of the mandible 2- Any single action of the mandible is the product of the closely integrated and highly coordinated performance of several jaw muscles 3- In a symmetrical movement the homologous muscles on either side are synergists and antagonists in an asymmetrical movement 4- The simplified classification of mandibular movement is usually described as follow: elevation, depression, protrude, retrude, and lateral movement, however, the real movements are complex patterns in which many of the single movement are combined 5- The branches of mandibular nerve (V-3 cranial nerve) control and regulate activities of all jaw muscles except the geniohyoid muscle by hypoglossal nerve (XII cranial nerve) WWW.HOANGTUHUNG.COM The Jaw muscles consist of: The elevator muscles: ‒ The (two) masseter muscle(s) ‒ The (two) medial (internal) pterygoid muscle(s) ‒ The (two) temporal muscle(s) The depressor muscles: ‒ The (two) lateral pterygoid muscle(s) ‒ The suprahyoid muscles ‒ The (two) digastric muscle(s) ‒ The (two) mylohyoid muscle(s) ‒ The (two) geniohyoid muscle(s) WWW.HOANGTUHUNG.COM The masseter The elevator muscles - The masseter - The medial pterygoid - The temporal Origin: - Superficial part: anterior two-thirds of zygomatic arch - Deep part: interior surface of zygomatic arch Insertion: - Superficial part: mandibular angle - Deep part: mandibular ramus Action: Elevates the mandible Superficial part involved in protrusion WWW.HOANGTUHUNG.COM The medial pterygoid muscle The elevator muscles - The masseter - The medial pterygoid - The temporal Origin: pterygoid fossa and maxillary tuberosity Insertion: medial aspect of mandibular angle and distal aspect of the ramus Action: Elevates the mandible and involved in lateral movements WWW.HOANGTUHUNG.COM The temporal muscle The elevator muscles - The masseter - The medial pterygoid - The temporal Origin: portions ‒ Temporal portion: temporal fossa ‒ Fascial portion: temporal fascia ‒ Zygomatic portion: internal aspect of zygomatic arch Insertion: internal aspect of coronoid process and anterior margin of the ramus Action: elevates the mandible anterior belly involve in protrusion) posterior belly retracts the mandible Temporal muscle is the most sensitive muscle with the occlusal interferences WWW.HOANGTUHUNG.COM The lateral pterygoid muscle Lateral pterygoid m Superior belly Inferior belly Medial pterygiod m buccinator The depressor muscles: ‒ The lateral pterygoid muscle ‒ The suprahyoid muscles ‒ The digastric muscle ‒ The mylohyoid muscle ‒ The geniohyoid muscle Origin: - Superior belly (Sb): lower surface of sphenoid - Inferior belly (Ib): 3/4 inferior of lateral aspect of lateral lamina of pterygoid process Insertion: - Sb: anterior portion of the disc and capsule - Ib: pterygoid fossa of the neck of the mandible Action: Sb contracts during retrusion and closing of mouth Ib contracts in protrusion and opening of mouth If only one side contracts: contralateral lateral movement WWW.HOANGTUHUNG.COM The digastric muscle Origin: mastoid notch (posterior belly) Insertion: digastric fossa of mandible (anterior belly) An intermediate tendon is between the anterior and the posterior belly that is attached by a fascial looplike strip to the hyoid Action: - When the hyoid bone is fixed (by suprahyoid and infrahyoid muscles): the mandible is depressed and pulled backward - When mandible is stabilized: digastric and other suprahyoid elevate the hyoid bone and the floor of mouth, which is necessary for deglutition The depressor muscles: ‒ The lateral pterygoid muscle ‒ The suprahyoid muscles ‒ The digastric muscle ‒ The mylohyoid muscle ‒ The geniohyoid muscle WWW.HOANGTUHUNG.COM the mylohyoid muscle Origin: mandibular mylohyoid line Insertion: mylohyoid raphe and hyoid body Action: depresses mandibular, elevates floor of mouth and hyoid bone Anatomically: forms the floor of the mouth, separating it from suprahyoid region The depressor muscles: ‒ The lateral pterygoid muscle ‒ The suprahyoid muscles ‒ The digastric muscle ‒ The mylohyoid muscle ‒ The geniohyoid muscle The geniohyoid muscle Origin: inferior genial tubercle Insertion: body of hyoid Action: contributes to mylohyoid muscle action WWW.HOANGTUHUNG.COM