Case study: treating a hypertrophic masseter muscle with botulinum toxin
Shad Jaff and Andrew Culbard present a case study using botulinum toxin to correct a hypertrophic masseter muscle
The case study follows the pair’s earlier explanation of the use of botulinum toxin to alter the aesthetics of the jawline.
The case we see here was a 28-year-old female fitness model who was highly active in the gym and competitive weight lifting. Her main complaint was that the muscle growth and development she was trying to achieve on her body also had an impact on her face, and we note very thick and hypertrophic masseters, an increased lower face width, prominent jaw contour (Figure 1).
All of these characteristics are usually not associated with feminine characteristics. Generally speaking, a male face is expected to be more square, whilst a females should be more V- or U-shaped, with a narrower bigonial width. However, this is region specific, subjective and varies from culture to culture.
In this case, a 20-unit dose of onabotulinum toxin type A was used. The clinician may want to increase or decrease this dose depending on muscle mass and desired atrophy.
Anatomical considerations in treating the masseter muscle include thickness of the muscle and avoidance of unwanted structures such as adjacent muscles, the facial artery, facial nerve, parotid gland and parotid duct.
Muscle thickness: the mean thickness of the masseter muscle was reported as 13.0mm (+/-1.8mm) in females and 15.1mm (+/- 1.9mm) in males. In an individual with hypertrophy, these measurements may be higher. Clinically, this is of importance as injections should be both superficial (5-10mm, five units) and deep (10-20mm supra-periosteal, five units) ideally with a 20mm 30-guage needle.
Safe injection zone: the masseter should be demarcated with a pencil on the skin. The anterior border can be palpated on clenching of the teeth and is most obvious at the body of the mandible (Figure 2). It will run perpendicularly from the mandible in a superior direction, corresponding to the masseteric cutaneous ligament. Injection anterior to this would risk diffusion into undated muscles such as buccinator and risorius.
Posteriorly, the border corresponds to the angle of the mandible, running superiorly and parallel to the anterior border (Figure 2). Injection posterior to this point is likely to compromise the parotid gland. Finally, our superior landmark is a line from the tragus of the ear to the commissure of the mouth, which corresponds to the pathway of the parotid duct.
Injections should be kept below this line to avoid damage to the parotid duct and facial nerve.
Figures 3 and 4 show before and after at a four-week review. We note significant decrease in muscle tonicity and activity and the patient also notes reduced tension in the muscle, and a decrease in clenching and grinding of the teeth.
The patient reported a high satisfaction from the treatment and indicated repeated treatments in the future.
As with any botulinum toxin treatment, we can expect a 12-week modulation, with a longer lasting clinical result due to muscle atrophy and habit modification.
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Park MY, Ahn KY, Jung DS (2003). Botulinum toxin type A treatment for contouring of the lower face. Dermatol Surg 29(5):477-483
Xie Y, Zhou J, Li H, Cheng C, Herrler T, Li Q (2014) Classification of masseter hypertrophy for tailored botulinum toxin type A treatment. Plast Reconstr Surg 134(2): 209e-218e
Dr Shad Jaff BDS graduated from Glasgow University with commendation in dental surgery and has been working in a mixed private and NHS practice in Glasgow since. Shad has established two aesthetics clinics in Lanarkshire.
Dr Andrew Culbard BDS MJDF RCS Eng is co-founder and clinical director of Face UK. He was awarded his BDS from study at the University of Glasgow Dental School and later gained membership to the Royal College of Surgeons of England in 2015. A practicing cosmetic dentist, Andrew is also an injectables trainer and has lectured for medical organisations around the UK.
This article was originally published in the June 2017 issue of Aesthetic Dentistry Today. Read more articles like this in Aesthetic Dentistry Today and gain three hours’ verifiable CPD with every issue. Click here to subscribe or call 01923 851 777. Get in touch via Twitter @AesDenToday or facebook.com/AesDenToday.