Botox jabs in the jaw are big business: the paralysing effect is widely used to prevent tooth grinding, and by cosmetic doctors to slim the lower face.
The treatment reduces the size of the masseter muscles, the large chewing muscles located on the jaw in front of the ears, and can cause dramatic cosmetic changes in a matter of weeks.
Jawline narrowing treatment, marketed as V-line contouring because of the shape it gives the lower face, is hugely popular around the world – even in the UK the procedure is available in hundreds of clinics.
Botox is widely used to reduce the size of masseter muscles, the large chewing muscles on the jaw
The jabs are also used to treat teeth-grinding (‘bruxism’). Grinding not only damages the teeth, but some dentists and doctors believe it can also cause headaches and facial pain, known as temporomandibular joint disorder (TMD) or temporomandibular joint pain (TMJ pain).
Injecting botulinum toxin (Botox is the best-known product) into the masseter muscles means you’re unable to bite down with the same force. Sometimes Botox is also injected into the temporalis, a fan-shaped muscle that runs from the outer forehead to behind the ear, which is also involved in chewing.
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In 2012 a review in the International Dental Journal found botulinum toxin jabs were as effective as a mouthguard in reducing grinding and associated pain.
However, evidence is emerging that the treatment may trigger a dramatic loss of bone density in the jaw, with parts losing up to 40 per cent of bone volume after a single treatment. What’s more, nobody knows when, or if, the weakened bone will fully regain its strength.
But evidence is emerging that the treatment may trigger loss of bone density [file photo]
One of those leading research in the field is Dr Karen Raphael, professor of oral and maxillofacial pathology at New York University College of Dentistry. She became concerned after reading animal studies which showed dramatic losses in bone after Botox for these conditions.
‘These studies generally find dramatic changes in bone quality and volume, particularly in the mandibular condyle after just a single injection of Botox.’ The condyle is the thinnest part of the lower jaw.
In a 2012 study in the journal Bone, rabbits were injected with botulinum toxin on one side of the jaw. Researchers found that after four weeks, the bone in the injected side was ‘severely decreased’. Three months later only half the lost bone was restored. Last July another study in the same journal found injecting botulinum toxin into the masseter and temporalis in rats led to a 20 per cent loss of bone from the part of the lower jawbone that supports the teeth.
6m
The number in the UK thought to have bruxism
Researchers said that in humans the bone loss could be ‘a risk factor for fractures’.
Normally, changes caused by Botox are assumed to be temporary, but as early as 2004, doctors noticed changes to the jaw were long-lasting. Yet TMD and facial slimming patients are encouraged to repeat treatments every 12 weeks.
‘The typical cycle of treatment every three months is probably insufficient for full bone mass recovery,’ says Dr Raphael.
She conducted a small study of seven women who’d had at least two Botox treatments for TMD pain in the past year. They were studied with nine patients with the condition who’d never had Botox.
All the Botox patients had reduced bone density in their jaw; none of the others did. Dr Raphael has since started a larger trial with government funding.
So how might Botox be linked to bone loss? Our bones are constantly renewed – old bone is dissolved, while new bone is being made by cells called osteoblasts. They produce new bone in response to tugging by muscles and impact.
But when masseter activity is reduced by Botox it can’t push and pull the jaw as powerfully, reducing the amount of bone remodelling and thus bone density, explains Caroline Mills, consultant maxillofacial and facial plastic surgeon at Wexham Park Hospital, Berkshire.
‘A colleague recently saw a patient who had Botox in the masseter for ten years and has discovered her jaw joint is literally melting away.’
The loss of bone in the jaw is linked to an increased risk of loose or lost teeth.
Miss Mills says side-effects of long-term Botox use in the jaw could include pain, increased risk of jaw fracture and even the need for joint replacement. She says doctors and dentists offer the treatment in good faith but may fail to warn patients of this risk because they themselves are unaware of it.
However, Miss Mills says some of her patients have relief from jaw pain with botulinum toxin injections and may feel the benefits of the treatment outweigh the risks.
Professor Damian Walmsley, scientific advisor to the British Dental Association, says ‘more rigorous randomised controlled trials’ are needed before we can categorically say what is happening.
Allergan, the company that manufactures Botox, told us: ‘It’s important to note that Botox is not approved in the UK for the treatment of bruxism, temporomandibular muscle and joint disorder or for slimming of the lower face.
‘While there are studies exploring the effects of muscle weakening on bone density, the clinical significance of these findings is unclear.’
Allergan is conducting studies exploring the safety and efficacy of Botox when injected into the masseter muscle, the company added.