Four Muscles of Mastication

For those reading the article in the AMTA magazine, who want a little more information about musculature, here's a quick review of the four muscles of mastication: masseter, temporalis and the pterygoids.

The Inner and Outer Slings of the Jaw

Two of the muscles that suspend the jaw are well-known to most massage practitioners—the masseter and temporalis. The masseter spans from the cheek bone (zygomatic arch) to the angle of the mandible. It is a dense, multilayered muscle with a reputation—the strongest muscle in the body for its size. It closes, clenches, bites, and grinds; with it, we can “hold our tongue” by closing our mouth or “mull things over” ruminating til we’re ready to speak.

 

The temporalis forms a fan of fibers on either side of the head. The belly crosses the TMJ just in front of the ear, and dives beneath the cheekbone to attach to the coronoid process of the mandible (the thin flange at the upper, anterior aspect of the ramus). This is the muscle that we instinctively rub at the temples when we get a headache. If we look closely at its shape, we can see how the anterior (and more vertical) fibers assist the masseter in closing the jaw, while the posterior (more horizontal) fibers draw the mandible back, setting the bone in the joint. The temporalis can “rein in” the mouth—anatomically in full closure of the TMJ, or metaphorically in inhibition of self-expression. Together, the masseter and temporalis create the “set of the jaw” and everything that that implies, from anger and aggression to tenderness and vulnerability (think of the quivering chin at the brink of tears).

 

Less known to practitioners and clients alike is an inner sling created by the pterygoid muscles. (The “p” is silent, as in pterydactyl. Both words derive from the root word ‘wing’—in this case, the wing of the sphenoid bone deep in the skull). There are two muscles—the medial and lateral pterygoid—each with a distinct path and function.

 

The medial pterygoid is the larger and more accessible of the two. It lies on the medial aspect of the mandible, anchoring on the angle and rising toward the roof of the mouth. (In this illustration, you’re looking at the right medial pterygoid ‘through’ the inside of the mouth.) Think of its relationship with the masseter this way: if you were to make a “v” with your index and middle finger, then imagine the jaw bone resting between them where they meet, one finger could be the masseter and the other the medial pterygoid. Along with closing the jaw, the medial pterygoid works with the masseter to create grinding, that side-to-side, round-and-round movement that horses and cows do so well.

 

The lateral pterygoid is tucked away behind the upper jaw, making it a little tricky to get to but well worth the effort. To imagine its location, let’s first get oriented to the TMJ: bring both hands up to your cheeks, Macaulay Culkin-style (with your index finger pad at the hole of each ear). If you slowly open your mouth, the condyle of the TMJ will rise up just beneath your middle finger. That condyle is one attachment of the lateral pterygoid; the other is at the top of the roof of the mouth, covered over by the soft palate (pterygoid plate of the sphenoid).

 

The lateral pterygoid is a relatively small muscle, with two bellies (one inferior, one superior), and because of its structure, it plays a key role in TMJ function. The most unusual anatomical feature of the TMJ is its highly mobile articular disc. The upper surface of the joint (the temporal fossa) is curved like a spoon, and the disc rides that curve from front to back and can even move forward out of the fossa if needed (as in taking an extra large anaconda-style bite). How does the disc do it? The superior belly of the lateral pterygoid reaches into the joint and attaches to the disc, drawing it forward when we open the jaw and allowing it to ease back when we close the jaw. If the lateral pterygoid becomes chronically shortened or immobile, the disc can’t move properly, and mouths open with strain, pain, pops or limitation.

 

Notoriously tight and tender, the lateral pterygoid is often the key to releasing the jaw fully, but working on it can be challenging. In 15 years of practice, I have yet to meet a client for whom this work isn’t intense (i.e., painful)—and remarkably effective. Once clients feel the ease of movement and decreased tension that’s possible, they are “on board” and often come back requesting for more of that specific treatment. And, although these muscles can be initially confusing to find in one’s own mouth, it can be very useful to teach clients to massage them as part of their home care.