DLI Muscle Resection: Causes, Symptoms, Treatment Methods

The lips are among the most expressive and noticeable features of the face. However, disorders affecting the DLI (Depressor Labii Inferioris) muscle, which controls the downward movement of the lower lip, can lead to noticeable facial asymmetry, disruption of facial balance, and dissatisfaction with one’s appearance. In some individuals, these conditions are congenital, while in others they may develop later as a result of facial paralysis, facial nerve injury, trauma, or synkinesis. When one side of the lower lip moves differently from the other during speaking, smiling, or making facial expressions, it can create both functional challenges and emotional discomfort.

Today, various treatment options are available for DLI muscle disorders, ranging from Botox injections to surgical interventions. Among these treatments, DLI muscle resection has emerged as an effective surgical option for suitable candidates, aiming to improve lower lip balance and restore facial symmetry. But what causes DLI muscle disorders, what symptoms do they produce, and which treatment methods are available? In this article, we will explore DLI muscle disorders in detail, covering their causes, symptoms, diagnosis, treatment options, and recovery process to help you better understand this condition and its management.

What is DLI Muscle Disorder?

DLI (Depressor Labii Inferioris) muscle dysfunction is a functional and aesthetic condition that occurs when the muscle responsible for pulling the lower lip downward does not function normally. As a result, asymmetry in lower lip movement may develop, leading to a noticeable imbalance between the two sides of the face, particularly during speaking, smiling, or facial expressions. DLI muscle dysfunction may be congenital or may develop as a result of facial paralysis, facial nerve injury, trauma, or synkinesis following facial paralysis. Patients may experience symptoms such as excessive downward pulling of one side of the lower lip, loss of smile symmetry, and overall facial imbalance. Since this condition can affect both facial aesthetics and a person's social confidence, it may be corrected through surgical or non-surgical treatment options in appropriately selected patients.

Causes of DLI Muscle Problems

The causes of DLI (Depressor Labii Inferioris) muscle disorders can generally be divided into two main categories: congenital causes and acquired causes. 

Congenital Causes

• Congenital underdevelopment (hypoplasia) of the DLI muscle
• Partial or complete absence of the DLI muscle at birth
• Congenital facial nerve developmental abnormalities
• Congenital lower lip asymmetry
• Genetic or hereditary muscle development disorders
• Congenital facial asymmetries
• Facial muscle abnormalities associated with congenital syndromes
• Developmental variations of the muscle or nerve during fetal growth
• Congenital unilateral limitation of lower lip movement
• DLI muscle dysfunction related to congenital facial nerve weakness

Causes that Develop Later

• Muscle imbalance following facial paralysis (Bell’s palsy)
• Facial nerve damage associated with Ramsay Hunt syndrome
• Trauma-related muscle or nerve injuries
• Complications following facial or oral surgical procedures
• Functional loss after facial nerve tumors or tumor-related surgeries
• Facial muscle dysfunction following a stroke
• Muscle weakness or atrophy due to long-standing facial nerve paralysis
• Synkinesis (involuntary simultaneous facial movements) following facial nerve recovery
• Neurological disorders affecting facial muscle control
• Nerve damage caused by infections
• Scar tissue formation (fibrosis) within the muscle or surrounding tissues
• Age-related changes affecting facial muscle balance
• Temporary muscle imbalance following Botox or other aesthetic treatments
• Neuromuscular disorders affecting muscle function
• Systemic diseases or traumatic injuries that impact the facial nerve function.

Symptoms of DLI Muscle Problems

DLI muscle dysfunction has several common signs and symptoms. While these symptoms may vary from person to person, they do not appear with the same severity in every individual. To better understand this condition, the most common symptoms include the following;

• One side of the lower lip pulling downward more than the other
• Noticeable facial asymmetry while smiling
• Imbalance in lower lip movements
• Uneven lip movement during speech
• Facial asymmetry at rest
• Irregular movements around the mouth during facial expressions
• Aesthetic imbalance in the lower part of the face
• Excessive or involuntary movement of the lower lip
• Uneven mouth corners when smiling
• Lower lip asymmetry following facial paralysis
• Involuntary muscle contractions associated with synkinesis
• Difficulty expressing emotions naturally
• Noticeable facial asymmetry in photographs or videos
• Hesitation to smile in social situations
• Aesthetic concerns that may affect self-confidence
• Difficulty controlling the lower lip while speaking or eating
• A pulling sensation in the lower lip during facial movements
• Uneven muscle activity around the mouth
• One side of the face appearing more active than the other
• Disruption of natural facial expressions and facial harmony

How is DLI Muscle Disorder Diagnosed?

The diagnosis of DLI (Depressor Labii Inferioris) muscle dysfunction is primarily based on a comprehensive facial examination and detailed analysis of facial expressions. During this evaluation, the physician assesses the patient's facial symmetry at rest while also observing how the muscles function during activities such as speaking, smiling, showing the teeth, pursing the lips, and pulling the lower lip downward. This is important because weakness, overactivity, or complete dysfunction of the DLI muscle can result in noticeable asymmetry of the lower lip. In particular, limited movement of one side of the lower lip or excessive downward pulling compared to the opposite side during smiling is considered a significant diagnostic finding.

In addition to the physical examination, further testing may be required if facial paralysis, facial nerve injury, or an underlying neurological condition is suspected. In such cases, electromyography (EMG) can be used to evaluate muscle and nerve function. Furthermore, detailed analysis of facial movements through photographs and video recordings may be helpful in certain patients. In congenital DLI muscle dysfunction, the patient’s medical history and the presence of facial asymmetry since childhood can provide valuable diagnostic clues. In acquired cases, factors such as trauma, previous surgical procedures, or a history of facial paralysis are carefully reviewed. Accurate diagnosis is essential for determining the most appropriate treatment approach and achieving the best possible restoration of facial symmetry.

What is DLI Muscle Resection?

DLI (Depressor Labii Inferioris) muscle resection is a surgical procedure in which a portion of the DLI muscle, responsible for pulling the lower lip downward, is removed or weakened. This operation is typically performed in patients who experience significant lower lip asymmetry, facial imbalance following facial paralysis, or aesthetic and functional concerns caused by excessive activity of the DLI muscle.

During DLI muscle resection, the surgeon aims to reduce the pulling force of the muscle by removing or weakening a specific portion of it through an intraoral approach or another appropriate surgical technique. As a result, lower lip movements become more balanced, and facial symmetry is improved. When performed in carefully selected patients, DLI muscle resection can be considered a permanent treatment option that helps restore facial harmony and improve overall facial balance.

Who is a Candidate for DLI Muscle Resection?

There are several patient groups who may be suitable candidates for DLI muscle resection. To examine these candidates in more detail, they include the following:

• Individuals with noticeable asymmetry in lower lip movements
• Patients whose lower lip is pulled downward more on one side than the other when smiling
• Individuals experiencing lower lip imbalance following facial paralysis
• Patients with abnormal DLI muscle activity caused by facial nerve injury
• Individuals with lower lip asymmetry due to synkinesis (involuntary simultaneous muscle movements) that developed after facial paralysis
• Patients with congenital DLI muscle dysfunction resulting in loss of symmetry in lower lip movements
• Individuals with aesthetic concerns related to overactivity of the DLI muscle
• People who experience discomfort from lower lip movements while speaking, smiling, or making facial expressions
• Patients who have not achieved satisfactory results from temporary treatments such as Botox 
• Individuals seeking a permanent solution and who are medically suitable for surgical treatment
• Patients who wish to improve facial symmetry and achieve a more balanced appearance of the lower lip
• Individuals in whom specialist evaluation has identified the DLI muscle as the primary cause of the asymmetry
• Patients who are in good general health and have realistic expectations regarding the procedure
• Individuals who have previously undergone treatment for facial paralysis but continue to experience persistent lower lip asymmetry
• Patients seeking correction of lower lip position for both functional and aesthetic reasons.

How is DLI Muscle Resection Performed?

DLI (Depressor Labii Inferioris) muscle resection is a surgical procedure performed to reduce lower lip asymmetry and improve overall facial balance. The procedure is typically carried out through the following steps:

1. Patient Evaluation and Surgical Planning

Before surgery, a comprehensive facial assessment is performed. The surgeon evaluates facial symmetry both at rest and during facial expressions such as smiling, speaking, and lip movement. The role of the DLI muscle in causing the asymmetry is carefully analyzed, and a personalized surgical plan is created. In some cases, photographs, video analysis, or electromyography (EMG) may be used for further evaluation.

2. Administration of Anesthesia

DLI muscle resection can be performed under local anesthesia with sedation or, in some cases, under general anesthesia. The choice of anesthesia depends on the patient's needs and the surgeon’s preference.

3. Preparation of the Surgical Area

The mouth and surrounding tissues are sterilized, and the surgical site is carefully prepared. The planned treatment area is identified and marked before the procedure begins.

4. Accessing the DLI Muscle

The surgeon typically reaches the DLI muscle through a small incision inside the mouth. This intraoral approach minimizes the risk of visible external scarring.

5. Identification and Assessment of the Muscle

The DLI muscle is carefully exposed while preserving the surrounding facial muscles and nerves. The specific portion of the muscle responsible for the asymmetry is identified.

6. Performing the Muscle Resection

According to the surgical plan, a selected portion of the DLI muscle is removed or weakened. The goal is to reduce the excessive downward pull of the lower lip and create more balanced and symmetrical movement.

7. Symmetry Assessment

After the resection is completed, the surgeon reassesses the position and movement of the lower lip. Minor adjustments may be made to achieve the most natural and symmetrical result possible.

8. Closure of the Incision

The surgical site is closed using absorbable sutures. Because the incision is usually made inside the mouth, no visible external scar is typically left behind.

9. Recovery and Follow-Up

Most patients can return home on the same day as the procedure. Mild swelling, tightness, or discomfort may occur during the first few days after surgery. Follow-up appointments are scheduled to monitor healing and evaluate improvements in facial symmetry. As swelling subsides, the final results become more apparent, and many patients experience long-lasting or permanent improvement in lower lip balance and facial harmony.

Recovery Process After DLI Muscle Resection

Recovery after DLI (Depressor Labii Inferioris) muscle resection is generally straightforward and progresses gradually over several weeks and months. While recovery timelines may vary from patient to patient, the process typically follows these stages:

First 24 Hours: Mild swelling, tightness, and minor discomfort are common immediately after surgery. Most patients are discharged on the same day. Resting and following the surgeon’s postoperative instructions are important during this initial period.

First 3 Days: Swelling and mild bruising may become more noticeable. Patients may experience temporary tenderness or slight changes in lower lip movement. Maintaining proper oral hygiene and taking prescribed medications as directed are essential during this stage.

First Week: A significant portion of the swelling begins to subside. Most patients can gradually return to their normal daily activities. Any discomfort while speaking or eating usually starts to improve.

Second Week: The healing process accelerates, and the tissues inside the mouth recover substantially. Lower lip movements begin to feel more natural, and most patients can comfortably resume their social activities.

Weeks 3–4: Most of the swelling resolves, and improvements in facial symmetry become more visible. Lower lip movements continue to balance out, resulting in better coordination of facial expressions.

Months 1–3: Internal tissue healing continues, and the muscles adapt to their new functional position. Surgical outcomes become increasingly apparent, and facial expressions typically appear more natural and symmetrical.

Months 3–6: The results of the procedure become more stable. Lower lip movement is generally well-balanced, and the improvement in facial symmetry can be more accurately evaluated. Most patients are close to their final outcome during this period.

6 Months and Beyond: The healing process is considered largely complete. Tissue maturation has finished, and the final results of the surgery are fully visible. With appropriate patient selection and proper surgical technique, the improvement in facial symmetry is often long-lasting and may be permanent.

Advantages of DLI Muscle Resection

DLI muscle resection offers several potential advantages for appropriately selected patients. To examine these benefits in more detail, they include the following;

• May help reduce lower lip asymmetry.
• Can improve overall facial symmetry and balance.
• May create a more harmonious appearance when smiling.
• Can reduce excessive downward pulling of the lower lip.
• May help correct certain lower lip imbalances that develop after facial paralysis.
• Can address aesthetic concerns caused by overactivity of the DLI muscle.
• May contribute to more balanced and natural facial expressions during speaking and smiling.
• Can provide longer-lasting results compared to temporary treatments.
• May be considered a permanent treatment option in appropriate candidates.
• Can enhance the natural appearance of facial movements and expressions.
• May improve self-confidence and social comfort.
• Can reduce aesthetic concerns related to uneven lower lip movement.
• Since the procedure is often performed through an intraoral approach, the risk of visible scarring is minimal.
• Most patients can return to their daily activities relatively quickly.
• Personalized surgical planning can help achieve the desired level of facial symmetry.
• May reduce the need for repeated treatments such as Botox injections.
• Can create a more balanced and harmonious appearance of the lower face.
• When performed on suitable candidates using appropriate surgical techniques, it can result in high patient satisfaction.

Risks and Potential Complications of DLI Muscle Resection

Complications may occur after DLI muscle resection, depending on the individual patient. Some of these complications can be associated with inadequate postoperative care or failure to follow recovery instructions. For this reason, it is important to pay close attention to the postoperative care process and follow the surgeon’s recommendations carefully. Potential complications may include the following:

• Temporary swelling after the procedure
• Mild to moderate pain or discomfort in the surgical area
• Development of bruising and tenderness
• Temporary stiffness of the lower lip during the healing process
• Temporary restriction of lower lip movements
• Temporary coordination difficulties affecting lip movements
• Delayed healing of the intraoral incision site
• Formation of unexpected scar tissue (fibrosis)
• Variations in results depending on the patient's healing process and individual tissue characteristics

DLI Muscle Resection or Botox?

Both Botox and DLI (Depressor Labii Inferioris) muscle resection are effective treatment options for correcting lower lip asymmetry caused by abnormal DLI muscle activity. However, the most appropriate choice depends on the severity of the asymmetry, the underlying cause, and the patient’s goals and expectations. Botox is a minimally invasive treatment that temporarily weakens the overactive DLI muscle. Because it does not require surgery, can be performed quickly, and involves little to no recovery time, it is often considered a first-line treatment option. However, the effects of Botox are temporary and must be repeated at regular intervals to maintain the results.

DLI muscle resection, on the other hand, aims to provide a more permanent solution by surgically removing or weakening a portion of the muscle. It may be particularly beneficial for patients with significant lower lip asymmetry following facial paralysis, long-standing synkinesis, or cases where Botox has not provided sufficient improvement. Although surgery requires a recovery period, it can offer long-lasting or even permanent results when performed on carefully selected patients. For this reason, Botox may be a suitable initial treatment for mild to moderate cases, while DLI muscle resection may be a more effective option when a more significant and lasting correction is desired. The most appropriate treatment approach should always be determined through a comprehensive facial evaluation and consultation with a qualified specialist.

If you would like to learn more about DLI muscle resection, you can contact Dr. Berke Özücer and his team, who specialize in facial paralysis treatment.