MUSCLES of MASTICATION Prof. Peter Stanko, MD, PhD Oral and Maxillofacial Surgeon Dpt. of Stomatology & Maxillofacial Surgery Comenius University, St Elisabeth Hospital

MUSCLES of MASTICATION The muscles that move the mandible (lower jaw) are also known as masticatory muscles because they are involved in bitting and chewing. Through chewing, or mastication (Lat. masticare = to chew) the tongue manipulates food and the teeth grind it.

Movements in TMJ 1. Elevation (adduction, closing of the mouth) 2. Depression (abduction, opening of the mouth) 3. Protraction (propulsion, movement of the mandible forward), it must be preceded by a mild mouth opening avoid overjet of the upper frontal teeth) 4. Retraction (retropulsion, , movement of the mandible backward) which has minimal extent (above 1 mm) 5., 6. Lateropulsions i. e. sinistropulsion (movement to the left) and dextropulsion (movement to the right).

Elevation of the mandible and other actions (functions) of the masticatory muscles Elevation of the mandible i. e. mouth closing is the general action (function) of the masticatory muscles. = Adductio (with exception of the pterygoid lateral muscle) →→→ elevators. 2. Oposite the group of suprahyoid muscles (musc. digastricus, musc. geniohyoideus, musc. mylohyoideus, musc. stylohyoideus) depresses the mandible i. e. they have function to open the mouth. = Abductio (with exception of the stylohyoid muscle) →→→ depressors.

1./ Musc. masseter a/Pars superficialis (origin = os zygomaticum and maxilla; lower insertion = tuberositas masseterica), course: oblique (backward) b/Pars profunda (origin = arcus zygomaticus; insertion = ramus mandibulae), course: vertical; Action of the masseter muscle – elevates the mandible (Lat. adductio, closing mouth), assists in protracting (Lat. propulsio) of the mandible

2./ Musc. temporalis a/Mesial part (origin = lamina superficialis fasciae temporalis; insertion = proc. muscularis or coronoideus mandibulae), course: vertical b/Distal part (origin = squama ossis temporalis; insertion = proc. muscularis or coronoideus mandibulae), course: oblique (mesially); Action of the temporal muscle – elevates the mandible + retraction (Lat. repulsio)

3./ Musc. pterygoideus medialis Origin = tuber maxillae; Insertion = tuberositas pterygoidea mandibulae), course: vertical (more exactly oblique downwards laterally); Action of the pterygoid medial muscle – elevates the mandibulae + moves it from side to side (Lat. lateropulsio) → active is the medial pterygoid muscle from the opposite side

4./ Musc. pterygoideus lateralis Origin = ala major ossis sphenoidalis, lamina lateralis proc. pterygoidei; Insertion = fovea pterygoidea on the condylar process of mandibulae), course: horizontal; Action of the lateral pterygoid muscle – protraction of the mandibulae (bilaterally or unilaterally → active is the lateral pterygoid muscle from the opposite side).

INNERVATION of masticatory muscles Innervation of all masticatory muscles is supplied by mandibular division of the trigeminal nerve (n. V./3).

BLOOD SUPPLY of masticatory muscles Blood supply of masticatory muscles = by a. maxillaris (end branch of a. carotis externa) -pars mandibulartis -pars pterygoidea (-pars pterygopalatina...more for supply of maxilla, palate, nose + orbit ).

INFLUENCE of the masticatory muscles on DISLOCATION ● The two groups of muscles (elevators, depressors) together with extrinsic tongue muscles may have influence on dislocation of bone fragments of the mandible by injury. ● The influence of muscles on dislocation by maxillary fractures is minimal, because muscles of the facial expression are gentle. ► The dislocation depends on insertion site of the certain muscle or muscles.

UNFAVORABLE vs. FAVOURABLE course of fracture line in mand. angle

Vertical dislocation of frontal fragment of the mandible (traum Vertical dislocation of frontal fragment of the mandible (traum. open bite) Suprahyoid muscles (abductors)

Horizontal dislocation of frontal fragment of the mandible Musc. GENIOHYOIDEUS