Square Jaw Botox: Why You Must First Identify the Cause Among Jawbone, Muscle, and Fat

Botulinum toxin injections for a square jaw are a procedure that reduces the volume of the masseter muscle, the jaw muscle used for chewing. Therefore, it is considered when the cause of an angular jaw is muscle; if the cause is jawbone or fat, other methods are considered alongside it. Before the procedure, we first determine what causes the angular jaw.

When the lower face appears angular, it is easy to assume that the jawbone is large or that there is excess cheek fat. However, an angular jaw can involve a combination of the shape of the jawbone, the development of the masseter muscle used for chewing, and fat in the cheeks and jawline—and different causes require different approaches. Here is an overview of how the causes of an angular jaw are categorized, how botulinum toxin acts on the masseter muscle, and what is evaluated during a consultation.

AI-generated image for illustrative purposes.

Categorizing the Causes of an Angular Jaw First

The causes of an angular jaw can generally be divided into three categories: jawbone, muscle, and fat. In some cases, only one factor is present, while in others, two or three coexist.

An illustration depicting the three causes of an angular jaw. From left to right: a prominent mandibular angle, an enlarged masseter muscle on the sides of the jaw, and excess fat in the cheeks and beneath the chin. This is an AI-generated image for illustrative purposes.

• Jawbone — When the angular portion of the lower jawbone is broadly developed outward
• Muscle (Masseter) — When the jaw muscle used for chewing is enlarged, causing the sides of the jaw to bulge
• Fat — When excess or sagging cheek or chin fat makes the lower face appear wide

Among these, botulinum toxin injections are considered when muscle is the cause. If the jawbone or fat is the cause, the extent of change achieved solely by injecting into the muscle may be limited.

Here is the key point — Because not every angular jaw responds to the same approach, it is essential to first identify whether the cause is muscle, bone, or fat.

Botulinum Toxin Reduces Volume by Limiting Masseter Movement

Botulinum toxin is a medication produced by purifying type A toxin made by Clostridium botulinum. It weakens muscle movement by blocking the release of acetylcholine, a substance that transmits signals from nerve endings telling the muscle to contract. When applied to muscles that create expression lines, such as the forehead or between the brows, it reduces wrinkling; when used on bulky muscles like the masseter, it serves to reduce muscle volume.

The principle is similar to exercise. Consistent workout enlarges arm and chest muscles, while taking a break from exercise for several months allows the muscles to shrink back to their original size. When botulinum toxin is injected into the masseter muscle, the muscle moves less, and its size decreases accordingly.

A photo illustrating an injection into the muscle area on the side of the jaw. The injection sites and dosage are determined after examination.

About a week after the procedure, you may feel some discomfort when chewing hard food. This occurs because the biting power of the masseter muscle has weakened, so it is helpful to be aware of this beforehand.

How the Square Jaw Botulinum Toxin Procedure Is Performed

• Design after consultation — The injection sites are determined after assessing the position and degree of masseter muscle development.
• Anesthesia — Anesthesia is performed using numbing cream or an ice pack.
• Injection — Botulinum toxin is injected into the designed areas. The procedure takes under 10 minutes.
• After the procedure — Results can be noticed starting about 7 to 10 days later.

The shape of the jawline and the duration of results can vary depending on the injection sites and dosage. That is why the treatment is designed based on the degree of masseter muscle development.

When Jawbone or Fat Is the Cause, Other Methods Are Considered

If fat is the cause, methods that address fat are considered. When there is excess subcutaneous fat such as cheek fat or a double chin, injecting fat-dissolving medication via Face Slimming Injection, or, when the buccal fat pad—a fat pocket located deeper than the chewing muscle—is prominent, removing fat through a small incision inside the mouth via Buccal Fat Removal is considered.

If the jawbone itself is broadly developed, the extent of change achieved solely by injecting into the muscle may be limited. Therefore, both facial shape and jawbone structure are evaluated during the consultation.

APEX Plastic Surgery's Botox·Face Slimming Injection·Buccal Fat Removal guidelines. The actual method is determined after examination.

Please keep in mind — After the procedure, side effects such as bruising, swelling, pain at the injection site, infection, asymmetry, or a sensation of weakened chewing power may occur. The onset and duration of results vary from person to person. Precautions will be explained in detail during your consultation.

For a Square Jaw, the Underlying Cause Must Be Identified First

“While the causes of a square jaw may include a large jawbone, sagging cheek tissue, or excess fat, the masseter—the jaw muscle we use for chewing—also accounts for a major portion of a square jaw. Therefore, it is important to consult with a board-certified plastic surgeon to determine the exact cause of your angular facial shape and find the most effective treatment.” — Chief Surgeon Song Hyun-seok

Frequently Asked Questions

Is botulinum toxin injection suitable for everyone with a square jaw?

Botulinum toxin injections are considered when the cause of an angular jaw is the development of the masseter muscle. If jawbone or fat is the cause, the extent of improvement achieved solely by injecting into the muscle may be limited, so we identify the cause first.

When can results be noticed?

Results can be noticed starting about 7 to 10 days later. The degree and rate at which the muscle reduces in size as its movement decreases vary by individual.

How long do the results last?

According to APEX Plastic Surgery's guidelines, the treatment cycle for botulinum toxin injected into muscle is approximately 6 to 10 months. The duration may vary depending on the injection sites, dosage, and muscle condition.

Could it be uncomfortable to chew food after the procedure?

About a week after the procedure, you may feel some discomfort when chewing hard foods. This is because the strength of the masseter muscle has weakened.

What is the procedure time and anesthesia method?

At APEX Plastic Surgery, the botulinum toxin procedure takes within 10 minutes, uses anesthetic cream or ice packs for anesthesia, and requires no hospitalization or stitch removal. This may vary depending on the patient's condition and the treatment area.

For a square jaw, treatment is determined by analyzing muscle, bone, and fat separately

What we examine first during consultation

• Masseter muscle — How prominently the jaw muscles bulge when clenching the teeth
• Jawbone — The angle of the lower jawbone and facial shape
• Cheek and jaw fat — How much cheek fat, jawline fat, and buccal fat are present
• Asymmetry between sides — Whether the degree of jaw development differs between both sides
• Previous procedures — Whether you have had botulinum toxin injections before, and when
• Facial harmony — Whether the jawline harmonizes with facial proportions and overall appearance

At APEX Plastic Surgery, board-certified plastic surgeon Dr. Song Hyun-seok provides all consultations and treatments.

Song Hyun-seok, Head Director · Board-Certified Plastic Surgeon, Ph.D.

This post is intended to provide medical information, does not guarantee specific treatment results, and does not replace medical consultation by medical staff. The featured image and the illustration of square jaw causes are AI-generated images created to aid understanding and do not depict real individuals; the injection scene is a photograph for procedural guidance. None of the images in this article are before-and-after comparison photos. Procedure duration, anesthesia, treatment intervals, etc., are based on the treatment guides on the APEX Plastic Surgery website and may vary by individual. As general side effects that may occur after procedures, such as bruising, swelling, and infection, can vary in severity depending on the individual, caution is advised. Please ensure you receive thorough consultation, explanation, and consent prior to the procedure.