Injecting to Treat Masseter Hypertrophy or Facial Slimming

Muscles Involved and Action

The masseter muscle is a thick, rectangular muscle of mastication, and it’s one of the strongest muscles in the body. It has two parts, superficial and deep, which play a crucial role in closing the jaw by elevating the mandible. Hypertrophy of the masseter muscle can lead to an undesired square-shaped facial appearance.


The masseter muscle can be easily identified when the patient clenches their teeth, as it becomes more prominent. To inject the masseter muscle, draw a line from the corner of the mouth to the tip of the earlobe (superior margin), and another line from the corner of the mouth to the angle of the mandible (inferior margin). The two vertical lines (anterior and posterior margin) that shape the outline of the masseter muscle will cross-hatch these two lines. 

Botulinum Toxin Injection Technique for Masseter Hypertrophy

The injection technique for masseter hypertrophy involves a biphasic approach, where 4 units of Botulinum toxin is released into both the deep and superficial belly of the masseter muscle at the same injection site. This technique has been performed successfully in numerous treatments, with patients showing significant improvement in facial slimming.

Complications and Solutions

Complications from botulinum toxin injection into the masseter muscle can include temporary decrease in chewing power, asymmetry, sagging, or sunken lateral cheeks. These complications can be minimized by accurate anatomical knowledge, appropriate dosing, and correct injection location and depth. 

Paradoxical bulging of the muscle is a rare complication that can occur within a week after injection. This condition is related to a superficial overcompensation of the muscle as a reaction to the neurotoxic weakening of the deep layer fibers. To prevent this, a combination of superficial and deep injections is recommended, particularly in patients with a history of paradoxical bulging after receiving masseter toxin injections.

For more information about Comprehensive Guide to Botulinum Toxin Injection Training, contact us at or call us at (212) 470-8059.

Statement of Responsibility

Cosmetic Medical Training recognizes that many of the techniques and recommendations are for procedures that are considered off-label use.  Our recommendations are based on many textbooks, published articles, seminars, and practical knowledge and experience.  The authors have attempted to maintain up to date knowledge and information in this training manual with the current standard of care.  However, due to the continuing flow of new research and information relating to the drugs being used in this course, we recommend that you check with the manufacturer for any changes in the package inserts, warnings, and precautions.  All information and tools presented within this site are intended for educational purposes. We do not guarantee that the information will be completely accurate and up to date; therefore the authors will not be held responsible for any errors, omissions, or inaccuracies published.  Application of the knowledge is ultimately the responsibility of the practitioner.

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