Slimming the Masseters with Neuromodulator Injections

The skeletal structure of the lower face is framed by the chin and jawline. Among the aesthetic concerns associated with this area are a lack of definition and/or a desire to change the face shape. Injectable fillers, liposuction, and implants are options for improving definition or shape of the chin and jawline. Submental fat and/or skin laxity also contribute to the overall look of the jaw shape. In more extreme cases of fat deposition or skin sagging, deoxycholic acid injection, liposuction, or neck lifts are part of the tool box. In most cases, achieving best results requires a combination of treatments approach.

The Role for Neuromodulators

Use of injectable neuromodulators to target the masseters to modify the jaw contour is increasingly popular. The masseter is one of the muscles of mastication and is felt as a deep prominence along the jawline when the teeth are clenched. Individuals who clench their jaw or grind their teeth at night (bruxism) may report tightness of the masseter and enlargement of this muscle.

Injections of botulinum toxin to this area will act to weaken the masseter muscle. Functionally, this improves the pain that some people experience in their jaw and also alleviates uncomfortable night grinding. From a cosmetic perspective, this will also work to slim the muscle and create a narrower lower face and sleeker jaw appearance. It will take a face that is more rectangular in appearance and create a more oval shape.

With any injectable procedure, there are risks of infection, bruising, and pain. More significant risks associated with injection of botulinum toxin in this area are weakness of the muscle that can impact chewing. This is the most common side effect of this procedure, seen in approximately 30 percent of patients and often associated with use of higher doses of neuromodulators. It can occur one to four weeks after the treatment. Temporalis muscle hypertrophy—an overactivity and hypertrophy of another mastication muscle—may also occur. Treatment by an expert physician is critical to help reduce the risk for adverse events and to manage those that develop.

Onset of cosmetic effect is usually 10-14 days after injection. The duration of effect is three to four months, on average; repeat treatments are needed to maintain results.

Technique is Critical

The physician’s skill is critical to achieving best outcomes. Aesthetically, asymmetry can develop with treatment. Note that there may be size differences between the left and right masseters prior to treatment. That is why the assessment is so critical, including touching the muscle, assessing the patient and analyzing the bite, and taking standardized photos of each patient. Keeping this in mind allows me to adjust the dosage according to each patient’s individual underlying asymmetry. These details allow for optimization of the treatment.

Another potential aesthetic outcome is worsening of jowls or sagging. Worsened jowls can be seen due to overly rapid post-treatment masseter atrophy, which results in volume reduction and sagging of the overlying soft tissue envelope. This can especially be seen in patients with baseline laxity, thin skin, and in those over the age of 40. To prevent this side effect, I recommend a staged approach, employing an initial lower dose and multiple treatment sessions, spaced two to three weeks apart, and selecting the appropriate candidates for treatment. This allows appropriate time for muscular atrophy to occur and for the overlying skin to contract.

I also closely evaluate the platysma muscle. It may be beneficial to inject this muscle to help mitigate facial depressor action, making this sagging and jowling less likely in the proper candidates for treatment.

Another potential unwanted effect that can develop after treatment is paradoxical bulging of the masseter during chewing. This happens due to excessive compensation of the untreated superficial layer of the masseter muscle. A tendinous structure (deep inferior tendon (DIT)) located in the deeper part of the superficial masseter muscle layer is thought to block toxin diffusion from the deep layer to the superficial layer; therefore, the superficial layer may be unaffected and prone to overcompensation in the event of masseter weakness. If such bulging develops and is not improved about two weeks after the initial treatment, injection of approximately 5-10 units to the untreated superficial layer will help to correct this side effect.

Because side effects can be both functional and cosmetic, training is critical. I would not recommend administering botulinum toxin to the masseters without appropriate advanced training and observation. Courses are available through the AAD and ASDS and are conducted by Board Certified Dermatologists.

Harmonizing the Face

Neurotoxin to the masseters is great in combination with fillers for optimization of facial structure, depending on the patient’s goals and face shape. Overall, this is a wonderful treatment in the correct candidates. It can provide overall facial harmonization and enhancement and also help with bruxism.