What Is The Depressor Labii Inferioris?

It's time to learn about the depressor labii inferioris, which is the muscle that allows you to pull your lower lip down or to the side. Learning about the various muscles of the mouth facilitates a greater understanding of how your body systems work together to help you move and express your emotions.

Location and Function

When you pull your lower lip down or to the side, you activate your depressor labii inferioris, as stated in The Muscular System Manual. According to the Loyola University Medical Education Network, this facial muscle originates from the outer surface of the mandible (lower jaw) and stretches upward to attach to the skin of the lower lip. The mandibular branch of the facial nerve allows this muscle to feel sensations and move when signaled by the brain. Working together with the orbicularis oris, the depressor labii inferioris moves the lower lip, making it one of the key muscles used to form expressions of sorrow, doubt or irony, as The Muscular System Manual notes.

Causes of Facial Muscle Paralysis

• Bell's Palsy: Can you imagine not having the ability to control one or both sides of your face when you smile? According to the National Institute of Neurological Disorders and Stroke (NINDS), Bell's palsy is one type of temporary paralysis that can affect the muscles that the facial nerve controls, including the depressor labii inferioris. A patient's facial muscles may be weak or, in some cases, may not be able to contract at all, which affects their ability to make facial expressions. Bell's palsy can also disrupt your sense of taste and make your smile appear asymmetrical or crooked.
• Head Trauma: While Bell's palsy is the most common source of facial paralysis, a study in Craniomaxillofacial Trauma & Reconstruction notes that head trauma, as well as injuries arising from surgery, may damage the facial nerve and result in facial muscle paralysis. If the muscles in the lower face are affected, the patient may have difficulty eating, drinking and speaking.
• Tumors: According to the University of California San Francisco, tumors that press on the facial nerve may also cause facial paralysis, interfering with the muscles' ability to move when signaled by the brain. If you're unable to move your lower lip, your depressor labii inferioris may be one of the muscles affected.

Treatment for Muscle Paralysis

Dental professionals can assist in the diagnosis and treatment of problems that result in facial paralysis or the loss of muscle function. A study published in Annals of Otology, Rhinology & Laryngology found that medical providers had success injecting onabotulinum toxin A into the depressor labii inferioris to treat a patient with an asymmetric smile. The injection moved the muscle — and the lip — back to its proper position, thereby correcting the appearance of the patient's smile.

Mild cases of Bell's palsy may not require treatment, notes the NINDS, though a doctor may recommend medications or therapeutic treatments. A doctor may take MRI or CT scans to diagnose the cause of facial paralysis if there's a possibility the patient has a tumor, according to the University of California San Francisco.

If you're worried that your smile is asymmetrical or you experience facial paralysis of any kind, your dental and medical team can work with you to address the cause of the problem and restore the normal function of all the muscles that help you make expressions.