Anatomy of the mylohyoid muscle

The mylohyoid muscle is a flat, triangular sheet of muscle that forms the muscular floor of the mouth. It runs from the mandible to the hyoid bone, acting as a sling that supports the tongue and plays a key role in swallowing, speech, and maintaining airway patency. Understanding its anatomy is essential for dentists, surgeons, and speech therapists because its location near the sublingual and submandibular spaces makes it a common landmark in oral and neck procedures.

Location and Overview

• The mylohyoid muscle sits deep to the anterior belly of the digastric muscle and superficial to the geniohyoid and hyoglossus muscles.
• It forms the floor of the sublingual space and the roof of the submandibular space.
• Each side is paired and they meet at a midline raphe, creating a V‑shaped muscular hammock.
• Its position relative to the mylohyoid line on the mandible changes with age and dental status.

The mylohyoid is one of the suprahyoid muscles, meaning it lies above the hyoid bone. When it contracts, it elevates the hyoid bone and floor of the mouth, which is the first step in the pharyngeal phase of swallowing.

Anatomical Origins and Insertions

• Origin: The mylohyoid line on the inner surface of the mandible, running from the symphysis menti to the last molar.
• Insertion: The anterior fibers insert into the median raphe; the posterior fibers insert into the body of the hyoid bone.
• Action: Elevates the hyoid bone and floor of the mouth, depresses the mandible when the hyoid is fixed.
• Innervation: Nerve to mylohyoid (a branch of the inferior alveolar nerve, from the mandibular division of the trigeminal nerve, V3).

The mylohyoid muscle is sometimes called the muscular diaphragm of the floor of the mouth because it separates the oral cavity from the neck.

Innervation and Blood Supply

• The mylohyoid nerve accompanies the mylohyoid branch of the inferior alveolar artery and runs in the mylohyoid groove on the mandible.
• The sublingual artery and submental artery form anastomoses that supply both the muscle and the overlying mucosa.
• Venous drainage follows the corresponding veins into the facial and lingual venous systems.
• Lymphatic drainage from the region goes to the submandibular and deep cervical lymph nodes.

Because the nerve to mylohyoid also innervates the anterior belly of the digastric, any surgical damage near the mandibular angle can affect both muscles. This is a common consideration during dental implant placement or mandibular osteotomies.

Functions of the Mylohyoid Muscle

• Elevates the hyoid bone during swallowing, helping to close the airway and propel the bolus into the pharynx.
• Depresses the mandible when the hyoid is fixed – for example, when opening the mouth against resistance.
• Assists in tongue movement by stabilizing the floor of the mouth.
• Plays a role in speech articulation, especially for sounds that require precise tongue‑floor coordination.
• Provides a barrier that prevents food or liquid from entering the submandibular space.

A study of swallowing mechanics notes that the mylohyoid contracts about 0.2 seconds before the tongue thrust, making it one of the first muscles activated in the oral phase of deglutition.

During a yawn or forceful mouth opening, the mylohyoid works together with the digastric and geniohyoid to stabilize the hyoid bone. Without this coordination, the hyoid would be pulled upward asymmetrically, causing discomfort.

Clinical Significance

• Submandibular space infections: The mylohyoid acts as a barrier. An infection above it (sublingual space) can spread across the midline, while an infection below it (submandibular space) can spread into the neck.
• Mylohyoid ridge: A sharp bony ridge on the lingual side of the mandible that can become problematic for denture wearers. Pressure from a denture can irritate the mylohyoid attachment.
• Sublingual gland herniation: A defect in the mylohyoid muscle (often congenital) can allow the sublingual gland to herniate into the submandibular space, forming a ranula or a plunging ranula.
• Surgical landmark: In submandibular gland excision, the mylohyoid is retracted anteriorly to access the gland lying lateral to it.
• Anesthesia considerations: The mylohyoid nerve can be blocked during inferior alveolar nerve blocks. Incomplete anesthesia of the floor of the mouth may indicate a missed mylohyoid nerve branch.

Mylohyoid and Dental Implications

• During extraction of mandibular molars, the mylohyoid line is a landmark for avoiding damage to the lingual nerve.
• Implant placement in the posterior mandible must account for the mylohyoid muscle attachment to avoid perforation of the lingual cortical plate.
• Fractures of the mandible involving the mylohyoid line may require reduction to restore muscle function.

Relationship with Surrounding Structures

• Superiorly: sublingual gland, sublingual artery and vein, lingual nerve, and submandibular duct.
• Inferiorly: submandibular gland (superficial part), anterior belly of digastric, facial artery and vein.
• Medially: geniohyoid and genioglossus muscles, hyoglossus muscle.
• Laterally: the mandible and the medial pterygoid muscle.

The submandibular duct (Wharton’s duct) runs along the superior surface of the mylohyoid, then loops around its free posterior border to enter the submandibular gland. This tortuous path is why sialoliths often lodge at the duct’s bend near the mylohyoid edge.

Common Conditions Affecting the Mylohyoid

Mylohyoid Defect (Sublingual Gland Herniation)

• Asymptomatic in most cases, but can present as a soft swelling in the submandibular triangle.
• Ultrasound reveals a fluid‑filled cyst deep to the mylohyoid. Treatment may involve marsupialization or excision of the gland.

Mylohyoid Spasm or Trigger Points

• Can cause referred pain to the mandible, ear, or throat. Often mistaken for temporomandibular joint dysfunction.
• Manual therapy and dry needling are effective modalities.

Mylohyoid Line Exostoses

• Bony outgrowths along the mylohyoid line can cause ulceration of the tongue or floor of the mouth. Smoothing the ridge may be required for denture fit.

Diagnostic and Surgical Considerations

• Palpation of the mylohyoid is best done intraorally – the muscle can be felt as a firm band when the patient lifts the tongue against the palate.
• Imaging: CT and MRI can show the mylohyoid as a thin, contrast‑enhancing sheet separating the sublingual and submandibular spaces.
• In cleft palate repair or hyoid suspension surgery, the mylohyoid may be partially released to allow better access to the pharynx.
• During a submental flap harvest, the mylohyoid is preserved to maintain floor‑of‑mouth integrity.

Surgeons must be aware of the mylohyoid nerve’s course. In a neck dissection, care is taken to avoid injuring the nerve when mobilizing the submandibular gland. Injury results in weakness of the floor of the mouth and an asymmetric hyoid lift during swallowing.

Conclusion

The mylohyoid muscle is more than just a floor‑of‑mouth sling. Its intricate anatomy influences swallowing, speech, dental procedures, and neck infections. Whether you are a clinician assessing a sublingual swelling or a surgeon planning a mandibular osteotomy, understanding the origin, insertion, and relations of the mylohyoid muscle is indispensable. Its role as a barrier and a dynamic elevator makes it a key structure in both routine and complex orofacial interventions.

Frequently Asked Questions

What is the mylohyoid muscle?

The mylohyoid muscle is a flat, paired muscle that forms the floor of the mouth. It originates from the mylohyoid line of the mandible and inserts into the hyoid bone and a midline raphe.

What nerve supplies the mylohyoid muscle?

The nerve to mylohyoid, a branch of the inferior alveolar nerve (from the mandibular division of the trigeminal nerve, CN V3), provides motor innervation.

What is the main function of the mylohyoid muscle?

Its primary actions are elevating the hyoid bone and the floor of the mouth during swallowing, supporting the tongue, and assisting in mandibular depression when the hyoid is fixed.

Can the mylohyoid muscle cause pain?

Yes. Trigger points in the mylohyoid can refer pain to the mandibular teeth, ear, or throat. It can also be a source of tension‑type headaches in some individuals.

What is a mylohyoid defect?

A mylohyoid defect is a congenital or acquired gap in the muscle that allows the sublingual gland or fat to herniate into the submandibular space, often presenting as a ranula.

How is the mylohyoid muscle related to submandibular space infections?

The mylohyoid acts as a natural barrier. Infections above it (sublingual space) tend to stay confined, while infections below it (submandibular space) can spread toward the neck and airway.

What is the mylohyoid line?

The mylohyoid line is a bony ridge on the inner surface of the mandible that runs from the symphysis to the third molar area. It serves as the attachment site for the mylohyoid muscle.

Can the mylohyoid muscle be injured during dental surgery?

Yes. In lower third molar extractions or implant placement, the mylohyoid muscle can be torn or the mylohyoid nerve can be damaged, leading to floor‑of‑mouth weakness.

How do you examine the mylohyoid muscle?

Intraoral palpation with the index finger while the patient elevates the tongue against the palate allows the clinician to feel the muscle’s contraction and tone.

What exercises strengthen the mylohyoid muscle?

Swallowing exercises with the head raised (effortful swallow) and tongue‑to‑palate resistance drills help strengthen the mylohyoid. Speech therapy often includes these for patients with dysphagia.