Mylohyoid Muscle: Anatomy, Swallowing, and Surgery

The mylohyoid is a thin, flat muscle that forms the muscular floor of your mouth. It stretches from the inner surface of your lower jawbone to the hyoid bone in your throat, creating a sling-like partition that separates the space under your tongue from the tissues beneath your chin. Its most important everyday job is helping you swallow, but it also plays roles in speaking and stabilizing the jaw. What makes it especially interesting from a clinical standpoint is that it is far less uniform than anatomy textbooks suggest, with gaps and variations that affect everything from dental anesthesia to the spread of cysts and infections.

Where It Sits and How It Attaches

The mylohyoid sits in a layered stack of muscles beneath the floor of the mouth. It lies just below the geniohyoid muscle and above the front belly of the digastric muscle, which runs along the underside of the chin. Together, these muscles make up the suprahyoid group, a set of muscles that connect the jawbone to the horseshoe-shaped hyoid bone in the upper neck.

The muscle originates along a bony ridge on the inner surface of the mandible called the mylohyoid line. But detailed cadaver studies show the attachment is more complicated than the textbook version. The muscle also arises from the lingual surface of the mandibular symphysis, the midline junction at the front of the lower jaw, below a pair of bony bumps called the mental spines. The two sides of the mylohyoid meet along a fibrous seam in the midline called the mylohyoid raphe, which runs from the chin to the hyoid bone. This raphe represents the lowest line of the muscle and connects its front and back attachments.

In about half of specimens examined in one structural analysis, there was a gap in muscle attachment between the front part of the mylohyoid line and the symphysis attachment, meaning the anterior and central portions of the muscle were not continuous.¹ That kind of discontinuity matters a great deal for surgeons placing dental implants, because the muscle is supposed to act as a septum between the sublingual space above and the submandibular space below. Where the muscle is absent, those two compartments communicate freely.

How the Mylohyoid Powers Swallowing

Every time you swallow, the hyoid bone has to move upward and forward. This lifts the larynx, protects your airway, and helps push food toward the esophagus. The mylohyoid is one of the primary engines of that movement. Research on primate swallowing mechanics shows that hyoid elevation and protraction are driven by concentric activation and rotation of the posterior mylohyoid and both bellies of the digastric muscle, followed by contraction of the geniohyoid.² In other words, the mylohyoid is not just participating in the swallow; it is one of the muscles doing the heavy lifting in the first phase of the sequence.

Neuromuscular stimulation experiments in humans reinforce this picture. When the mylohyoid and nearby muscles were stimulated individually, each muscle produced roughly 30% of the laryngeal elevation seen during a normal swallow and about half the velocity. When pairs of muscles were stimulated together, the result jumped to around 50% of normal elevation and about 80% of the velocity.³ These numbers make clear that no single suprahyoid muscle handles the swallow alone. They work in concert, and the mylohyoid’s contribution is substantial but incomplete without its neighbors.

Because the mylohyoid is active during every swallow, it is also one of the main muscles picked up by surface electromyography (EMG) electrodes placed beneath the chin. Studies examining the submental surface EMG signal have confirmed that the primary contributors to that recording are the mylohyoid, the anterior belly of the digastric, and the geniohyoid.⁴ This is the basis for swallowing biofeedback therapy: clinicians use the submental EMG signal as a proxy for how hard the floor-of-mouth muscles are working, and patients can see the signal in real time while practicing swallowing exercises.

Head Posture and Swallowing Effort

One overlooked factor in mylohyoid performance is how you hold your head. A preliminary study comparing different sagittal neck postures found that a forward head posture was associated with higher peak mylohyoid amplitude during swallowing than a neutral head position.⁵ The implication is that slouching forward may force the mylohyoid to work harder to achieve the same laryngeal lift. For healthy adults this is unlikely to matter, but for people who already have marginal swallowing function, such as stroke survivors or older adults with age-related muscle loss, poor posture could tip the balance from a safe swallow to an unsafe one. Speech-language pathologists already emphasize upright posture during meals for patients at risk of aspiration, and this finding hints at one of the muscular mechanisms behind that advice.

Gaps, Holes, and Hernias in the Muscle

Anatomy textbooks typically illustrate the mylohyoid as a continuous muscular sheet. The reality is messier. A study examining CT scans of 100 individuals found mylohyoid defects in 77 of them.⁶ These openings, sometimes called “boutonnières” (the French word for buttonhole), can contain fat, blood vessels, salivary tissue, or some combination. They are not injuries or diseases. They are simply natural gaps where the muscle fibers never fully closed the floor of the mouth.

The clinical problem is that tissue poking through these holes can mimic tumors on imaging. When a sublingual gland herniates through a mylohyoid defect, it shows up on CT or MRI as a mass-like structure in the submandibular area. Researchers have found that people with mylohyoid defects had a significantly higher prevalence of sublingual gland herniation compared to those without defects.⁷ For radiologists who are not thinking about this possibility, the hernia can look like a worrisome mass that triggers unnecessary biopsies. Recognizing the mylohyoid boutonnière as a normal variant prevents alarm where none is warranted.

Plunging Ranulas and the Mylohyoid Gateway

A ranula is a type of cyst that forms in the floor of the mouth when a sublingual salivary gland duct gets blocked or ruptured. Most ranulas stay in the sublingual space, creating a visible bluish swelling under the tongue. But sometimes the collected saliva dives deeper, passing through or around the mylohyoid to balloon into the submandibular space beneath the chin. This is called a plunging ranula, and the mylohyoid is the anatomical gatekeeper that determines whether it happens.

There are several pathways by which this can occur. Saliva under pressure can squeeze through a pre-existing perforation in the mylohyoid muscle. Alternatively, the sublingual gland itself may project through the mylohyoid, or ectopic sublingual gland tissue may already exist on the cervical side of the muscle. Ducts of the sublingual gland that merge with the submandibular gland can also provide a route behind the mylohyoid.⁸ Postmortem investigation of mylohyoid anatomy supports the clinical evidence that the plunging ranula originates from the sublingual gland and enters the neck through the mylohyoid muscle, which is the rationale for treating the condition by removing the sublingual gland entirely rather than just draining the cyst.⁹

Given how common mylohyoid defects are, it is perhaps unsurprising that plunging ranulas, while still relatively uncommon overall, are a well-recognized complication in oral and maxillofacial surgery. The connection between natural gaps in the muscle and the cyst’s ability to descend underscores the point that the mylohyoid is not the impenetrable barrier it is often assumed to be.

Why Dental Numbing Sometimes Fails

Anyone who has had a lower molar worked on has probably experienced the inferior alveolar nerve (IAN) block, the classic injection that numbs the lower jaw, lower lip, and chin. It works well most of the time, but occasionally a patient’s lip goes numb and yet they still feel pain during the procedure. One long-suspected explanation involves the mylohyoid nerve.

The mylohyoid nerve is a branch of the mandibular division of the trigeminal nerve. Its textbook job is to supply the mylohyoid muscle and the front belly of the digastric. But anatomical variation means it sometimes also sends sensory fibers to the pulp of lower teeth, particularly the molars and premolars. When that happens, an IAN block does not catch all the sensory input, because some of it is arriving through the mylohyoid nerve, which splits off before the injection site.

Research on whether a supplemental mylohyoid nerve block fixes this problem has produced mixed results. One controlled study found that the mylohyoid nerve block alone did not predictably provide pulpal anesthesia in mandibular teeth and did not significantly enhance anesthesia when added to a standard IAN block.¹⁰ However, a simpler workaround has shown promise. A study evaluating patients who had pain despite a successful IAN block found that a small lingual submucosal injection near the offending tooth eliminated the pain in all cases, suggesting it caught whatever variant nerve fibers were sneaking through from the lingual side.¹¹

Meanwhile, a separate comparison trial found that a modified mylohyoid nerve anesthesia technique using 4% articaine with dexamethasone performed comparably to the conventional IAN block for mandibular molar surgery, with no significant differences in onset time, intraoperative pain, or quality of anesthesia.¹² The takeaway for patients is practical: if your dentist has trouble getting a lower molar numb, the issue may not be technique failure but nerve anatomy. A small supplemental injection on the tongue side of the gum often solves it.

The Mylohyoid as a Surgical Reconstruction Tool

Because the mylohyoid is a broad, flat muscle with a reliable blood supply, surgeons have found it useful as a local flap for closing defects after oral cancer surgery. In one series of 29 patients who underwent composite resection with marginal mandibulectomy, the mylohyoid advancement flap was used to close the surgical wound. Every single flap survived, a 100% success rate.¹³ The advantage of using a local muscle like the mylohyoid is that it avoids the complexity and donor-site morbidity of transferring tissue from a distant part of the body.

The muscle has also been combined with a submental island flap for more complex reconstructions. In patients with severe medication-related osteonecrosis of the jaw, a condition where bone in the jaw dies in response to certain drugs, surgeons have used the submental flap plus mylohyoid muscle to reconstruct the mandible after partial jaw removal. The approach proved effective for wound healing and showed potential for bone regeneration of the exposed bone surface.¹⁴ Using a nearby muscle with intact blood flow and nerve supply makes recovery faster and reduces the risk of flap failure compared to free tissue transfers from other body regions.

Anatomical Variations That Catch Surgeons Off Guard

Beyond the gaps already discussed, the mylohyoid can vary in ways that genuinely surprise experienced anatomists. One documented case involved a cadaver with two extra sheet-like muscles emerging from the intermediate tendon of the digastric muscle on both sides. These supernumerary muscles traveled forward and inserted at the mylohyoid raphe, forming a chevron shape with a 119-degree angle at the midline. An additional muscle belly emerged from the raphe and inserted near the midline on the outer surface of the mandible. All of the extra musculature was innervated by the mylohyoid nerve.¹⁵

Variations like these are more than anatomical curiosities. Extra muscle bellies can change the expected landmarks during surgery, potentially making it harder to identify the mylohyoid nerve or to predict where the sublingual and submandibular spaces communicate. For surgeons operating in the floor of the mouth, awareness that the mylohyoid is not always shaped the way the atlas shows is essential to avoiding inadvertent nerve damage or unexpected bleeding.

Rehabilitation After Radiation Damage

Head and neck cancer treatment often involves radiation therapy aimed at tumors in or near the oral cavity, and the mylohyoid frequently absorbs collateral damage. Radiation-induced fibrosis can stiffen the connective tissues around swallowing muscles and compress nearby peripheral nerves, contributing to reduced strength, limited flexibility, and in some cases actual denervation of the muscles involved in swallowing.¹⁶ The result is late-onset dysphagia, which means difficulty swallowing that appears months or years after treatment ends.

The MANTLE trial is investigating manual therapy as a way to address this problem. The treatment involves hands-on manipulation of the fibrotic tissues over 10 sessions across six weeks, paired with a home exercise program. The rationale is that loosening the fibrotic tissue may decompress the nerve tracts and restore some range of motion to muscles like the mylohyoid that have been stiffened by scar tissue. While the trial is still in pilot phases and firm efficacy data are not yet available, the approach highlights a growing recognition that radiation damage to the floor-of-mouth muscles is a treatable condition rather than an irreversible consequence of cancer therapy. For cancer survivors struggling with swallowing years after treatment, this line of research offers a concrete reason for optimism.