S8 Mastication - LabLink

Click here for a condensed, step-by-step dissection summary.

Locate and identify the relevant osteological features

Find these structures:

    • Zygomatic arch
    • Zygomatic bone
      • Temporal process
    • Parietal
      • Superior temporal line
      • Inferior temporal line
    • Temporal
      • Zygomatic process
      • Mandibular fossa
      • Articular tubercle
        • Petrotympanic fissure
      • Styloid process
    • Sphenoid
      • Greater wing
        • Foramen ovale
        • Spine of sphenoid bone
      • Pterygoid process
        • Lateral plate
        • Medial plate
          • Pterygoid hamulus
      • Pterygoid fossa
      • Pterygoid canal
      • Scaphoid fossa
      • Infratemporal crest
    • Maxilla
      • Maxillary tuberosity
    • Mandible
      • Neck
      • Ramus
        • Angle
        • Mandibular foramen
          • Lingula
        • Coronoid process
        • Condylar process
          • Neck
          • Pterygoid fovea
        • Mandibular notch
        • Retromolar fossa (“coronoid notch”)
        • Temporal crest

Clean the superficial part of the masseter m.

Find these structures:

  • Masseter m.

1.) Clean the superficial surface of the masseter m. This will involve the removal of the masseteric fascia. Completely remove the parotid gland while preserving the neurovasculature in this region.

Note: The masseter m. is a powerful elevator of the mandible, and is the most superficial muscle of mastication. The muscle is invested in masseteric fascia. The masseter is quadrangular, complexly layered about the lateral body and ramus of the mandible, and attaches these areas to the inferior margin of the zygomatic bone and the anterior portion of the zygomatic arch. When active, the masseter m. elevates, protracts, retracts, and laterally moves the mandible.

Note: The superficial part of the masseter m. is the largest component of the muscle. The muscle fibers are directed posteroinferior, attaching on the angle and border of the ramus of the mandible.

Photo 1. Superficial part of masseter m.

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Reflect the masseter m., and identify the buccinator m. and temporalis m.

Find these structures:

  • Masseter m.
  • Zygomatic arch
  • Zygomatic bone
    • Temporal process
  • Temporal bone
    • Zygomatic process
  • Mandible
    • Ramus
      • Coronoid process
      • Angle
  • Buccinator m.
  • Buccal fat pad
  • Masseteric n.
  • Masseteric a.
  • Temporalis m.
  • Temporal fascia
  • Temporomandibular joint
    • Stylomandibular ligament

2.) Bluntly separate the temporalis m. and temporal fascia from the zygomatic arch and the masseter m.

Note: Temporoparietal fascia is at the same level (but is not thought to be contiguous with) the SMAS, thus is is superficial to the temporal brs. of the facial n., and has likely been removed at this point in the dissection. The temporal fascia is deeper and denser, and it invests the temporalis m.

Photo 2: Procedural: removing fascia

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3.) Relieve the masseter m. from its proximal attachments (zygomatic arch and bone), and reflect the muscle inferiorly. Using either bone shears or a saw, cut through the zygomatic process of the temporal bone, just anterior to the articular tubercle of the temporal bone.

Photo 3. Procedural: cutting the zygomatic process of temporal bone

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4.) Relieve the zygomaticus major m. from its attachment to the zygomatic bone. Insert a blunt probe between the temporal process of the zygomatic bone and the maxilla. Saw through the temporal process of the zygomatic bone.

Photo 4. Procedural: cutting the temporal process of the zygomatic bone

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5.) Relieve the deep part of the masseter m. from the zygomatic arch, and remove the zygomatic arch to uncover the buccal fat pad and the inferior attachment of the temporalis m. to the coronoid process of the mandible.

Note: Nestled amongst the muscles of mastication is a variably sized and irregularly shaped, encapsulated buccal fat pad. In many individuals, the buccal fat pad provides substantial shape to the inferolateral face.

Photo 5. Buccal fat pad

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6.) If not previously dissected, remove the buccal fat pad, and clean the superficial aspect of the buccinator m., while leaving a portion of the parotid duct in place. Continue to clean the temporal fascia to reveal the tendon and belly of the temporalis m.

Photo 6. Buccinator and temporalis mm.

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7.) Locate the mandibular notch, and locate portions of the masseteric n. and a.

Note: The masseteric n. is a branch of the anterior trunk of the mandibular n. (V3), which innervates the deep side of the masseter m. The masseteric a. is a small branch of the maxillary a., which supplies the masseter m.

Photo 7. Masseteric neurovascular bundle

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8.) Palpate the styloid process of the temporal bone. Locate the stylomandibular ligament.

Note: The stylomandibular ligament is often considered a reinforcing ligament of the temporomandibular joint (TMJ); however, its alignment is such that it does not seem to afford any mechanical constraints to the joint. This ligament extends from the styloid process of the temporal bone to the posterior border of the ramus and angle of the mandible.

Photo 8. Stylomandibular ligament

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Reflect the temporalis m.

Find these structures:

  • Temporalis m.
  • Anterior deep temporal a.
  • Posterior deep temporal a.
  • Deep temporal nn.
  • Ramus of mandible
    • Coronoid process
  • Temporomandibular joint
    • Lateral ligament

9.) Using bone shears (and being mindful of structures deep), cut the base of the coronoid process of the mandible, and superiorly reflect the coronoid process and temporalis m. to above the level of mid-orbit. Be mindful not to cut the masseteric a. & n. Reflection of the temporalis m. is often difficult. Be mindful to preserve the underlying neurovasculature.

Note: The temporalis m. is invested by layers of fascia which can be very durable and thus difficult to remove. If time is limiting, or if the temporalis m. shreds with the removal of the fascia, feel free to not completely clean the muscle.

Photo 9. Procedural: cutting the coronoid process of the mandible

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10.) Locate the lateral ligament of the temporomandibular joint covering the condylar process of the mandible.

Note: The lateral (temporomandibular) ligament of the TMJ is important in restricting posterior and lateral movement of the condylar process of the mandible. It attaches the articular tubercle of the temporal bone to neck of the condylar process of the mandible. It completely covers the condylar process of the mandible and is intimately related to the articular capsule.

Photo 10. Lateral Ligament

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11.) Place a blunt probe immediately posterior to the condylar process of the mandible to protect deeper structures. Using either a handsaw or bone shears, cut through the base of the condylar process of the mandible adjacent to the mandibular notch.

Photo 11. Procedural: cutting the condylar process of the mandible

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12.) With the condylar process of the mandible cut, locate the inferior alveolar neurovascular bundle, and follow it inferiorly to the mandibular foramen. Taking care to preserve the inferior alveolar neurovascular bundle, use bone shears to cut the ramus of the mandible at or just above the mandibular foramen. Be aware not to cut the lingual n., which is also located in this region.

Photo 12. Ramus of mandible and mandibular foramen

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Note: The inferior alveolar neurovascular bundle contains the inferior alveolar n. (of V3), inferior alveolar a. (from maxillary a.), and the inferior alveolar v. (to maxillary v.). This bundle supplies the mandible and associated structures.

Photo 13. Procedural: cut ramus of the mandible

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13.) Locate the vascular supply (anterior & posterior deep temporal aa. & vv.) and innervation (deep temporal nn.) for the temporalis m.

Note: The temporalis m. is supplied by anterior & posterior temporal aa., which are branches of the maxillary a. Branches of the superficial temporal a. (middle temporal brs.) will also supply lateral portions of the temporalis m. Anterior & posterior temporal vv. accompany the same-named arteries.

Note: The deep temporal nn. innervate the temporalis m. These are small branches of the mandibular n. (V3), anterior division that are variable in number and distribution.

Photo 14. Neurovascular supply of temporalis m.

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Investigate the temporomandibular joint (TMJ)

Find these structures:

  • Temporomandibular joint (TMJ)
    • Lateral ligament
    • Articular capsule
    • Articular disc
    • Upper synovial cavity
    • Lower synovial cavity
    • Retro-articular tissue (retrodiscal pad/zone)

14.) Examine the temporomandibular joint (TMJ). Manipulate the condylar process to appreciate the motions possible at this joint. Clear the lateral ligament from the joint capsule. Remove the lateral aspect of the joint capsule to reveal the articular disc and the upper and lower synovial cavities. The sphenomandibular ligament has likely been removed but remnants may be present medial or inferior to the remnant of the condylar process of the mandible.

Photo 15. Temporomandibular joint

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Note: The temporomandibular joint (TMJ) is a compound synovial joint formed by the mandibular fossa of the temporal bone receiving the condylar process of the mandible. These structures are separated by an articular disc, which compounds the articulation into superior and inferior joints (and cavities).

Note: Protrusion and retraction movements take place in the superior joint, while the primary movement of the inferior joint includes elevation and depression with additional pivoting actions. The muscles of mastication produce the movements at the TMJ. The TMJ is primarily afferently innervated by the auriculotemporal n. and vascularized by branches from both the maxillary a. and the superficial temporal a.

Note: A sphenomandibular ligament extends from the lingula of the mandibular foramen to the spine of the sphenoid. This ligament is tense when the TMJ is in an intermediate position (slightly opened).

Note: The retro-articular tissue (retrodiscal pad/zone) is located between the posterior portion of the articular disc and the articular capsule, containing neurovasculature. This area is often a site of edema in TMD (TemporoMandibular Disorder). Typically, pain associated with TMD typically sources from the retro-articular tissue.

Clean the medial and lateral pterygoid mm.

Find these structures:

  • Lateral pterygoid m.
    • Superior head
    • Inferior head
  • Medial pterygoid m.
  • Maxillary a.
  • Nerve to lateral pterygoid
  • Nerve to medial pterygoid

15.) Identify the maxillary a., but do not dissect/identify its branches at this time. Protect this artery and its branches during the dissection of the lateral pterygoid m.

Note: The maxillary a. and the superficial temporal a. are the terminal branches of the external carotid a. The maxillary a. supplies the structures within the infratemporal fossa, muscle of mastication, the middle ear, meninges, and areas of the deep face with blood. The maxillary a. typically runs most of its proximal course superficial (lateral) to the lower head of the lateral pterygoid m. before diving deep to the muscle to terminate in the pterygomaxillary fissure. Another variation is the proximal maxillary a. courses deep (medial) to the lateral pterygoid m.

Photo 16. Maxillary a.

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16.) Clean the lateral pterygoid m. and medial pterygoid m. Distinguish between the superior and inferior heads of the lateral pterygoid m.

Note: The lateral pterygoid m. is comprised of two heads: a superior head (connecting the articular disc and capsule of the TMJ to the greater wing of the sphenoid) and an inferior head (connecting the pterygoid fovea of the mandible to the lateral aspect of the lateral pterygoid plate of the sphenoid). Both heads are innervated by the nerve to the lateral pterygoid, anterior division of the mandibular n. (V3). Both heads are supplied by pterygoid branches of the maxillary a. The heads of the lateral pterygoid m. are reciprocally innervated. When activated, the inferior head depresses the mandible (opens the mouth).

Note: The superior head of lateral pterygoid m. is activated during clenching of the mandible (when temporalis and masseter mm. are contracted). Osborn (1995) hypothesized that the superior head of the lateral pterygoid acts as a balancing muscle, one that enables the other muscles of mastication to achieve maximum bite force. Many sources describe that the superior head of the lateral pterygoid m. protracts the articular disc of the TMJ as a sliding joint for protrusion of the mandible. The precise actions of the superior head of the lateral pterygoid m. likely vary with variation of the attachments to: articular capsule and disc, condylar process of mandible, or both.

Note: The medial pterygoid m. has proximal attachments on the sphenoid, palatine, and maxillary bones; distal attachment is on the mandible, mirroring the masseter m. The nerve to medial pterygoid (V3) provides efferent innervation, and when contracted, this muscle assists in elevation as well as protrusion of the mandible.

Photo 17. Medial & lateral pterygoid mm.

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