Musculus masseter
The masseter is the principal muscle of mastication. It originates from the zygomatic arch and facial crest of the maxilla and inserts on the lateral surface of the ramus and angle of the mandible. It has superficial and deep portions. Its main actions are to close the jaw and produce the lateral grinding motion needed to process forage. It is innervated by the masseteric nerve (from the mandibular branch of the trigeminal nerve, CN V3). Horses chew thousands of times per day; the masseter is adapted for high force over a relatively short distance.
Origin: Zygomatic arch and facial crest of the maxilla
Insertion: Lateral surface of the ramus and angle of the mandible
Action: Closes the jaw; produces lateral grinding motion for mastication
Innervation: Masseteric nerve from mandibular branch of trigeminal (CN V3)
Masseter myopathy or pain can cause difficulty chewing, weight loss, or head-shyness. Dental problems that alter chewing patterns can overload the muscle. Trauma (for example from pulling back while tied) can also affect it.
## Overview Masseter myositis is inflammation of the cheek muscles causing painful swelling and difficulty opening the mouth (trismus). Horses drop feed and may lose weight. Causes include dental inf
## Overview Dental-related tension is chronic muscle tightness, often in the masseter or temporalis muscles, that results from oral pain caused by sharp enamel points, malocclusions, or other dental
## Overview Temporomandibular joint (TMJ) dysfunction is inflammation or misalignment of the jaw joint. It causes reluctance to chew, quidding, head tossing, resistance to the bit, tenderness over th
Difficulty chewing, dropping feed, or sensitivity over the jaw should be checked. Regular dental care helps keep the masseter working normally.
## Overview Masseter myositis is inflammation of the cheek muscles causing painful swelling and difficulty opening the mouth (trismus). Horses drop feed and may lose weight. Causes include dental infection, temporomandibular joint inflammation, trauma, or rarely immune-mediated disease. ## Causes Extension of dental or joint infection, trauma, or primary muscle inflammation. ## Diagnosis Palpation of firm, painful masseters, observation of restricted jaw opening, and investigation of the teeth and temporomandibular joints. ## Treatment Anti-inflammatories, treatment of any dental or joint infection, and soft feed. Immune-mediated cases may need corticosteroids. ## Recovery and Prognosis Good when the underlying cause is identified and treated. ## Prevention Regular dental care and prompt treatment of oral infections. Signs include: swollen firm jaw muscles; reluctance to open the mouth; dropping feed; weight loss; pain on palpation of the cheeks
## Overview Dental-related tension is chronic muscle tightness, often in the masseter or temporalis muscles, that results from oral pain caused by sharp enamel points, malocclusions, or other dental disease. Horses may chew on one side, develop asymmetric muscle bulk, or resist the bit. ## What It Indicates Underlying dental discomfort that alters chewing patterns and creates secondary muscle strain. ## Diagnosis Oral examination revealing sharp points or other pathology, plus observation of asymmetric chewing or muscle development. ## Treatment Correction of the dental problem (floating, addressing malocclusions). Muscle tension usually resolves once pain-free chewing is restored. ## Recovery and Prognosis Excellent after appropriate dental care. ## Prevention Regular dental examinations and floating. Signs include: one-sided chewing; asymmetric masseter bulk; head tilting while eating; quidding; bit resistance on one rein
## Overview Temporomandibular joint (TMJ) dysfunction is inflammation or misalignment of the jaw joint. It causes reluctance to chew, quidding, head tossing, resistance to the bit, tenderness over the temporal fossa, and visible muscle wasting above the eye. Dental problems or poor bitting often contribute. ## Causes Dental disease, trauma, or bit-related pressure. ## Diagnosis Palpation, dental examination, and sometimes radiographs or computed tomography of the TMJ. ## Treatment Correct dental issues, adjust bitting, anti-inflammatories, and physiotherapy. Injections are used in some cases. ## Recovery and Prognosis Good when the underlying cause is addressed. ## Prevention Regular dental care and appropriate bit fit. Signs include: reluctance to chew; quidding; head tossing; resistance to the bit; tenderness over the temporal fossa; muscle wasting above the eye
Masseter myopathy or pain can cause difficulty chewing, weight loss, or head-shyness. Dental problems that alter chewing patterns can overload the muscle. Trauma (for example from pulling back while tied) can also affect it.
Difficulty chewing, dropping feed, or sensitivity over the jaw should be checked. Regular dental care helps keep the masseter working normally.
See the Masseter on our interactive 3D horse model. Open 3D Model