Muscular anatomy: masseter, temporalis, medial and lateral pterygoid and buccinator muscles
Superficial layer: zygomatic bone and zygomatic arch --> mandibular ramus.
Middle layer: zygomatic arch --> mandibular ramus.
Deep layer: zygomatic arch --> mandibular ramus and coronoid process of the mandible. There is debate as to whether the masseter attaches to the articular disc of the TMJ.
Origin (superficial layer): temporal fossa, zygomatic bone, deep temporal fascia.
Origin (deep layer): superior surface of the zygomatic arch and the muscle that passes beneath the arch.
Insertion: mandible (coronoid process and ramus). It can attach on to the articular disc of the TMJ.
The sphenomandibularis is the deep belly of the temporalis muscle located on its medial side. It originates from the greater wing of the sphenoid and attaches on to the mandible at the temporal crest, the retromolar triangle and the anterior limit of the mandibular notch (Geers et al 2005).
Functions of the masseter and temporalis
Whilst the masseter and temporalis close the TMJ the temporalis pulls the condyle backwards. This is opposed by the upper head of the lateral pterygoid which pushes the condyle forwards during mouth closing.
Schmolke (1994) found the attachment of the temporalis fascia to the TMJ joint capusle and of the masseteric fascia to the TMJ articular disc to be much less extensive than the attachment of the lateral pterygoid muscle to the articular disc.
Therefore this author proposed the function of the temporalis and masseter muscles, because of their extensive complement of muscle spindles, may help to register the position of the articular disc. This would make them a part of the control system regulating the position of the various elements of the TMJ.
Another interesting finding was noted by Scmidt et al (2009) who found higher EMG activity in the right temporalis and suprahyoid muscles when the tongue was placed against the palate with slight pressure. Relaxation of the temporalis occured with resting the tongue on the floor of the mouth.
Origin (upper head): greater wing of sphenoid; (lower head): lateral pterygoid plate of sphenoid.
Insertion: neck of the mandible. A part of the upper head may be attached to the TMJ capsule and disc.
Actions: bilateral contraction results in opening and protrusion of the jaw i.e. the condyle being pulled forwards and slightly down. Only the lower head contracts during mouth opening whilst the upper head relaxes. The upper head pushes the condyle forwards during mouth closing opposing the backwards pull on the condyle from the temporalis.
Unilateral contraction results in the mandible deviating medially to the opposite side.
Origin (deep head): lateral pterygoid plate of the sphenoid; (superficial head): maxilla and palatine bone.
Action: elevates (and with the lateral pterygoid) protrudes the mandible. With the lateral pterygoid unilateral contraction results in the mandible deviating medially to the opposite direction.
Origin: alveolar processes of the maxilla, mandible and temperomandibular joint.
Insertion: Orbicularis oris. It has anatomical connections to the lateral deep slip of the platysma (Hur et al 2015), temporalis (Hur 207), incisivus labii inderioris (Hur et al 2011), zygomaticus major (Shim et al 2008) and parotid duct where it is associated with its function (Kang et al 2006).
At the aveolar process of the maxilla the buccinator blends with the superificial lamina of the masticatory facsia as it leaves the anterior border of the masseter (Gaughran 1957).
Fascia of the masticatory space (Gaughran 1957)
The masticator space is described as a fascial compartment containing:
- Lateral pterygoid.
- Medial pterygoid.
- Temporomandibular joint.
- Ramus of the mandible.
- Masticatory fat pad (corpus adiposum buccae).
- Neurovascular structures.
Inferiorly the fascia of the masticatory space is formed from the superficial lamina of the cervical fascia which attaches to the lower border of the mandible.
From the mandible attachment arises a deep and superficial sheet of fascia:
Deep sheet of fascia
The deep sheet of fascia passes upward on the inside of the medial pterygoid muscle (medial pterygoid fascia). This fascia passes upwards from its attachment to the mandible, over the medial pterygoid, to above the insertion of the pterygoid muscles attaching on the greater wing of the sphenoid (spine of sphenoid, jct of body/greater wing at the pterygoid process) and temporal bone (petrotympanic fissure) (Stecco 2015). It should be noted Stecco et al (2015) described these attachments for both the medial and lateral pterygoid fascia.
The superficial and deep layer of the fascia fuses:
- Posteriorly: at the rear edge of the ramus of the mandible.
- Anteriorly: along the anterior border of the masseter.
Superficial sheet of fascia
The superficial sheet of cervical fascia continues superiorly to cover the parotid gland (parotid fascia, Hinganu et al 2018) and masseter muscle (a dense masseteric fascia). The masseteric fascia attaches on to the articular disc of the TMJ (Schmolke 1994) and zygomatic arch (Gaughran 1957).
From the upper border of the zygomatic arch the fascia continues:
- Posteriorly and superiorly covering the temporal muscle (temporal fascia or temporal aponeurosis of Batson) attaching to the superior temporal line (Gaughran 1957).
- Anteriorly and superiorly it continues as the zygomatic fascia (Hinganu et al 2018).
Anteriorly the superficial fascia attaches on to the anterior border of the ramus of the mandible (possibly becoming continuous with the sheath of the lateral pterygoid muscle) and the buccinator fascia and maxilla.
The superficial and deep layer of the fascia fuses:
- Posteriorly: at the rear edge of the ramus of the mandible.
- Anteriorly: along the anterior border of the masseter muscle.
At the anterior border of the masseter the fusion of the superificial and deep fascia splits again into a deep and superficial layer of fascia.
Deep layer of fascia
The deep layer reflects around the anterior border of the masseter passing towards the anterior border of the mandibular ramus. Here it blends with the insertion of the temporalis muscle and attaches to the mandible. Extending superiorly it attaches to the epimysium of the temporalis muscle.
Superficial layer of fascia
Attaches to the maxilla blending with the buccinator fascia and attaches to the deep layer along the mandible
Interpterygoid, lateral pterygoid and temporalis fascia
The interpterygoid fascia extends between the pterygoid muscles sometimes reflecting onto the deep surface of the temporalis. It's pierced by the auriculotemporal nerve (Barker and Davies 1972) and merges with the main muscle of the tongue (styloglossus) and with the fascial system of the internal carotid artery (Bordoni 2020). Its attachments are (Barker and Davies 1972):
- Superiorly: cranial base at the sphenoid and temporal bone (Bordoni 2020 & Komune et al 2019) and the suture between the palatine and sphenoid (Lang 2001). Maxilla (Lang 2001).
- Posteriorly: extends between the lateral and medial pterygoid muscles.
- Inferiorly: mandible from above the upper border of medial ptcrygoid insertion extending backwards to the neck of the condyle. Here it blends with the stylomandibular fascia.
Forms the sphenomandibular ligament (spine of sphenoid --> mandible: lingula of the mandibular foramen). This ligament blends with the lateral pterygoid fascia (Lang 2001) and the discomalleoular ligament and anterior ligament of malleus (refer to 'relations of the TMJ to the middle ear') (Rowicki and Zakrzewska 2006).
- Anteriorly: the fascia is usually flimsy but it may be reflected to form a septum between the pterygoids and the fascia on the deep surface of the temporalis muscle. This is called temporopterygoid fascia.
Lateral pterygoid and the deep temporalis fascia are separated at their anterior and medial surfaces but are intimately united more posteriorly.
Lateral pterygoid fascia
The lateral pterygoid fascia is a triangular sheet. It extends over the lateral surface of the lateral pterygoid muscle (Lang 2001). Its attachments are:
- Anteriorly: sphenoid (lateral pterygoid plate) and buccinator fascia (Lang 2001).
- Superiorly: extends from the TMJ (lateral part of the capsule and disc) --> maxilla --> buccinator fascia --> sphenoid (greater wing)
- Inferiorly: mandible. Attaches to the medial surface of the mandibular ramus --> coronoid process (below temporalis attachment) --> mandibular notch --> TMJ: lateral part of the joint capsule.
The lateral pterygoid fascia blends with:
- Inferior attachment of the interpterygoid fascia at its attachments from the mandible to the TMJ.
- Sphenomandibular ligament (Lang 2001)
- Buccinator fascia (Lang 2001)
Schmolke (1994) found some collagen fibres separate from the lateral pterygoid fascia to attach to the same region as the upper lamina of the articular disc at the petrotympanic fissure. Separate fibres have been observed extending through the petrotympanic fissure into the anterior ligament of the malleus within the tympanic cavity (refer 'relations of the TMJ to the middle ear').
Deep temporal fascia
The deep temporal fascia covers the anterior surface of the temporalis. It blends with the epimysium above the level of the mandibular attachment at the coronoid process (Gaughran 1957), lateral ligament of the TMJ and TMJ joint capsule (Schmolke 1994). The fascia covering the temporalis tendons extends further down the mandible to attach on to the oblique line of the mandible and blend with the buccinator fascia.
The deep temporalis and lateral pterygoid fascia fuse at:
- Mandible: oblique line of the mandible.
- Deep temporal fascia extends from the medial edge of the anterior border of the temporalis tendon posteriorly to fuse with the lateral pterygoid fascia.
Because of this fusion the attachment of the deep temporal fascia to the base of the skull can be considered as being identical with that of the lateral pterygoid fascia. The areas of fusion between the deep temporal and lateral pterygoid fascia are:
- Between the upper and lower heads of the lateral pterygoid muscle. Within the fascia at this level is the buccal nerve and several anterior deep temporal branches of trigeminal nerve (V3).
- Superior to the upper and lower heads of the lateral pterygoid, the two fascia usually remain united underneath the temporalis muscle. The buccal nerve emerges superior to the upper head or between the upper and lower heads of the lateral pterygoid muscle. It passes within the fused lateral pterygoid and deep temporalis fascia, to lie against or imbedded within the most medial fibers of the deep part of the temporalis muscle.
Relations of the TMJ to the middle ear
Discomalleolar ligament (mandibular-malleolar ligament or the “tiny” Pinto ligament)
Rowicki and Zakrzewska (2006) found this ligament to be a fibroelastic tissue connecting the TMJ capsule and articular disc to the malleus. It extends from the TMJ and the sphenomandibular ligament* --> through the petrotympanic fissure --> malleus.
The discomalleolar ligament can attach to the anterior ligament of malleus (Rowicki and Zakrzewska 2006).
Ligaments of malleus
There are three ligaments of malleus:
- Anterior ligament of malleus (Casserio’s ligament): malleus --> anterior wall of the tympanic cavity close to the petrotympanic fissure. Some of the fibers also pass through the fissure to the spine of sphenoid. Within the pterotympanic fissue the anterior ligament of malleus becomes continuous with the sphenomandibular ligament* (Rowicki and Zakrzewska 2006)
- Lateral ligament of malleus: malleus --> roof of the tympanic cavity.
- Superior ligament of malleus: malleus --> roof of the tympanic cavity.
Both the discomalleolar ligament and anterior ligament of malleus pass through the petrotympanic fissure that connects the TMJ through the temporal bone into the tympanic cavity.
Schmolke (1994) and Rowicki and Zakrzewska (2006) found the TMJ articular disc is tightly fixed to the border of the petrotympanic fissure. Fibres extend through the petrotympanic fissure into the anterior ligament of the malleus within the tympanic cavity.
The petrotympanic fissure also serves as an attachment for the pterygoid fascia (Stecco et al 2015).
* Sphenomandibular ligament: spine of sphenoid --> mandible: lingula of the mandibular foramen. It is formed from the interpterygoid fascia. As well as attaching to the discomalleolar and anterior ligament of malleus it also blends with the lateral pterygoid fascia (Lang 2001).
FASCIAE OF THE MASTICATOR SPACE (1957) GEORGE R. L. GAUGHRAN
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The deep belly of the temporalis muscle: an anatomical, histological and MRI study (2005). C. Geers Æ C. Nyssen-Behets Æ G. Cosnard Æ B. Lengele
Anatomical considerations on the masseteric fascia and superficial muscular aponeurotic system (2018) DELIA HÎNGANU, CRISTINEL IONEL STAN, CORINA CIUPILAN, MARIUS VALERIU HÎNGANU
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Inferior bundle (fourth band) of the buccinator and the incisivus labii inferioris muscle. (2011). Hur MS, Hu KS, Kwak HH, Lee KS, Kim HJ.
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