The masseter muscle is a very large and thick muscle that occupies the outside of the  mandible back by the angle of the jaw. It is one of the major muscles responsible for moving the jaw. Because of where it is located, it can contribute significantly to fullness of the lower face. When it is enlarged or naturally larger (as in some ethnic groups), it can be extraordinarily obvious and contribute to a more square facial shape.

Reduction of a large masseter muscle has historically been difficult. Surgical reduction is possible but it is associated with a significant amount of swelling and a long recovery period. Restricted oral opening and persistent trismus make a subtotal myectomy of the masseter very unappealing.

Botulinum toxin type A, Botox or Dysport, has been used off-label for masseter muscle treatment for some time. Anectodal reports abound that it is effective for visible muscle reduction with repeated injections. In my Indianapolis plastic surgery experience, I use it regularly and my observations is that it does work by visible and photographic assessments. Numerous clinical reports have also been published that support its effectiveness which date back to as early as 2001. The question is not whether it works but are its effects sustained? Must the injections be continued forever or is there a point where the injections are not needed to sustain the effect?

In the June 2010 issue of Plastic and Reconstructive Surgery, these very questions were addressed by Dr. Kim and colleagues from Seoul, Korea. They studied retrospectively 121 patients who were treated for more than one year with botulinum injections (Dysport) into the masseter muscles. (100u to 140 u per side) The patient’s masseter muscle thickness was measured by ultrasonography. The patients received variable numbers of injections from two to eight. Overall masseter muscle size was reduced from roughly 13.5 to just under 10 mms. With increasing number of injections came further muscle thickness reduction.

This study shows that sustained effect of masseter muscle reduction can be obtained by repeated muscle paralyzing injections. Because the sample size is inconsistent with irregular visit intervals and injection periods as well as patient ages and muscle thicknesses, no firm dose or injection interval could be specifically recommended. One interesting graph shown in the paper demonstrates a predictive relationship of the maximal effect and the sustained effect. This graph suggests that three injection sessions during the first year leads to a sustained muscle reduction effect. This sustained amount of muscle reduction is not as great as that seen in the first few months (maximum effect) but could be maintained out to greater than 36 months after the first year’s injections.

One of the interesting questions is why would masseter muscles shrink or reduce in size if the same thing is not seen with the muscles of facial expression? If botulinum toxins can reduce muscle volume, why do not wrinkle treatments need less toxin dose and are maintained longer with repeated injections? One very plausible explanation is that the type of muscle fibers are quite different. Muscles of facial expressions are faster twitch fibers and are structurally different than that of the master muscles. All facial muscles are not created equal. Another difference in the sustained effects between the two muscles is in how they recover. The assessment of facial expression muscle activity is when they start working again, The assessment of masseter muscle recovery from injection therapy is a change in size which is quite slower, thus the longer effect than that seen in wrinkle treatments.     

Dr. Barry Eppley

http://www.eppleyplasticsurgery.com

http://www.ologyspa.com

Indianapolis, Indiana

Botox or botulinum toxin A has a lot uses that go beyond facial wrinkle reduction. Some of these are well known and FDA-approved and others are not. One of the newer uses in plastic surgery has been in the nonsurgical management of masseter hypertrophy. While well known in the Eastern world, it is not as common in Western populations.

The muscle enlargement at the angle of the jaw gives one a square face or jaw look. In Asia, particularly Korean and Chinese populations, they have a naturally larger masseter muscles and broader bony jaw angles. When they become excessively so, which occurs in about 10 to 20% of the population, their face becomes too square or strong. This tendency appears to be a developmental or congenital one. . The incidence of masseteric hypertrophy in the Western population is unknown and is as likely to occur on just one side as it is bilateral. Many Caucasian patients have an associated history of bruxism or excessive jaw clenching which is clearly a contributing cause.

Masseteric hypertrophy can be simply and successfully treated with Botox injections. In my Indianapolis plastic surgery practice, I usually start out giving 25 units per masseter. This is relatively painless, done with a long 30 gauge needle which is introduced over the most prominent parts of the muscle near the jaw angle. The needle is introduced down to the bone where it is then retracted and injected. This makes sure that the injection is done into the muscle and not into the subcutaneous space. Usually about four or five injections are given per side based on feeling the most prominent parts of the muscle as the patient clenches.

In men and in most Asians, due to their inherently larger muscle mass, the initial injection is higher averaging 35 to 40 units. The injection methods remains the same.

In the masseter, the effects of Botox usually are felt in seven to ten days as one’s clenching and headaches are less noticeable. (if those symptoms existed beforehand) The muscle slimming effects become apparent in two to three months. It is quite surprising that the muscle mass could be reduced in such a short period of time, but I have seen it consistently occur. This improvement in facial shape is clearly evident by frontal photography as the affected sides become less square and more oval-shaped.

How long the effects of Botox last is variable. When it comes to pain relief from bruxism, I find that it lasts about the same length of time as for facial wrinkle relaxation, around four months or so. If aesthetic muscle reduction is the goal, the effects are longer and it is not necessary to re-inject until about six to nine months later.

The interesting questions are ……how long do the muscle slimming effects last once the Botox treatment stops…and are the muscle reducing effects permanent? There are no exact answers to these questions but I would find it hard to believe that maintenance injections are not necessary. I have had no bruxism patients, who over time, had their clenching cycle broken and have had a long time of relief. But I wouldn’t go so far as to say permanent.

Certainly Botox  injections are much more appealing than surgical debulking of the masseter muscle or mandibular angle bony reductions. With the recent introduction of a competitive analogue to Botox, Dysport, it will be interesting to see if its effects are longer lasting as purported.

Dr. Barry Eppley

http://www.eppleyplasticsurgery.com

http://www.ologyspa.com

Clarian North Medical Center, Carmel, Indiana

Clarian West Medical Center, Avon, Indiana

Indianapolis

Botox, the world’s most popular injectable cosmetic treatment, works by providing a temporary muscle paralyzing effect reducing or eliminating unwanted facial expressions. The vast majority of Botox used for this purpose is done in the forehead and around the eyes. In the masseter muscle, however, repeated Botox injections over time can actually reduce the size of this large muscle improving external appearance and reducing muscle-clenching pain symptoms.

 
The use of Botox for masseter muscle reduction is well chronicled in the Korean medical journals. In this ethnic group, it is often desired to reduce the size of the muscles for the cosmetic purpose of making the face look less square. Botox done over time is so effective that the surgery historically used to achieve the same effect, masseter muscle reduction and mandibular angle reduction, is now reserved only for patients that demonstrate an actual bony prominence as the primary source of the problem.

 
Botox injections in the masseter muscle are easy to do. Have the patient clench their teeth together and the prominent bulging of the masseter muscle borders are easily seen. I usually inject right into the prominent bulging areas with 6 units per bulged area and stay closer to the angle areas of the jaw and its lower border to avoid injecting into the parotid gland. Plus, the thickest bulk of the masseter muscle lies low anyway. I have found that it takes about 25 - 35 units per side to get a good effect. So when I run out of bulging areas to inject, I will make sure I inject at the front and back of the muscle at the bottom of the jaw until I reach that number of units.

 
While effects can be usually been fairly quick, as judged by less muscle pain and headaches, it takes about 6 months before actual visible shrinking of the muscle is seen. Botox injections should be repeated every 4 months up to a years worth of treatment to see the best results. The decreased size of the muscle is impressive after a year of Botox therapy. I have been surprised to see that the results of masseter muscle reduction seem to be maintained even if no further Botox injections are done. I don’t have a good physiologic explanation as to why that would be so, as Botox does not cause any permanent atrophy in the muscles of facial expression. But I have seen it enough now to realize that it is real clinical finding with Botox use.

 
Dr. Barry Eppley
http://www.eppleyplasticsurgery.com
http://www.ologyspa.com
Clarian North Medical Center, Carmel, Indiana
Clarian West Medical Center, Avon, Indiana
Indianapolis