From Volume 45, Issue 1, January 2018 | Pages 32-37
The use of Botulinum toxin (BTX) for cosmetic procedures has been well recognized, however, its popularity and use in treating a variety of conditions within clinical dentistry is continuing to increase. This includes masseteric hypertrophy, neuralgias, temporomandibular joint dysfunction and sialorrhoea, to name just a few.
The use of Botulinum toxin (BTX) for cosmetic treatments has been well recognized within the literature and commonly reflected in the media. However, the Botulinum toxin is derived from a variety of other therapeutic uses.1 With its increasing popularity in clinical dentistry and further developments in pharmacology, there has been increased understanding of the use of BTX to treat a variety of orofacial conditions. With further MHRA (Medicines and Healthcare products Regulatory Agency) approvals, the use and merit of BTX as a minimally invasive clinical adjunct to existing treatments is continuing to broaden the horizons of clinical dentistry.1
Botulinum toxin is produced from the bacterium Clostridium botulinum and is a neurotoxin of which there are seven subtypes, ranging from A–G.2 The most common forms of this toxin are Types A and B, which have multiple clinical applications.3
Over the past 30 years, the popularity of BTX has increased as the therapeutic potential has become apparent.2 The application of BTX for the successful treatment of different orofacial conditions is increasing where, traditionally, these conditions would have been managed by analgesics, anti-inflammatories and steroids.4
Botulinum toxin has a relatively simple mechanism of action. The neurotoxin consists of a heavy chain and light chain. On injection into striated muscles, a chemical reaction is initiated. The heavy chain of the BTX complex binds to the cholinergic nerve terminals of the muscle, whilst the light chain binds to specific proteins called SNARE (Soluble NSF Attachment Protein Receptor), which prevents the binding and release of acetylcholine into the synaptic cleft5 (Figure 1). By doing so, this induces temporary paralysis of muscles as well as inhibiting glandular secretions. When injected into muscle, paralysis can occur within 2–5 days and last for up to 3 months.5
There are multiple clinical uses for BTX and more are being discovered as trials and research continue to progress. The following sections discuss the most common uses for BTX injections in the head and neck, but the list is not extensive and more information can be found in reputable oral and maxillofacial surgery journals.
Over the years BTX injections have become one of the most requested cosmetic procedures in facial rejuvenation. Hyperkinetic lines (‘wrinkles’) are formed by repetitive contraction of the facial musculature.6 BTX injections can weaken or paralyse muscles of the face by inhibiting neurotransmission between peripheral nerve endings and muscle fibres. This, in turn, smooths the overlying skin and reduces the appearance of the hyperkinetic lines.2 The most common area for injection is the glabellar area between the eyebrows followed by the lines that occur lateral to the eyes, also known as ‘crow's feet’ (Figure 2).
Vertical maxillary excess (or ‘Gummy Smile’) is often an aesthetically displeasing occurrence with no simple treatment options. Surgical procedures (maxillary impaction), together with orthodontic treatment, are common procedures for correcting the excess, but are understandably invasive and time consuming. The lip elevator muscles determine how much lip elevation occurs during smiling, with over-contraction of these being a possible cause for excessive gingival show. BTX injections can be used to paralyse these muscles and limit over-contraction, resulting in a minimally invasive treatment for reduction of a ‘Gummy Smile’ (Figure 3).
Masseteric hypertrophy is the asymptomatic enlargement of one or both masseter muscles.7 Aetiology is unclear but is thought to be associated with malocclusion, TMD (temporomandibular disorder) and bruxism. Surgical partial excision of the masseter muscle has been a treatment modality for hypertrophy in the past, however, this was associated with complications, including haematoma, infection, trismus and facial nerve paralysis.8 In 1994, two studies introduced the technique of Botulinum toxin injections as a less invasive technique for the reduction in masseter contour.9,10 It works by interfering with the neurotransmitter mechanism of the muscle, causing atrophy due to selective paralysis.11,12,13 It should be noted that, whilst surgical excision of the muscle reduces the number of cells permanently, BTX injections only reduce the muscle volume temporarily, and so patients should therefore be fully informed of the potential risk of recurrence that can occur months after the initial treatment.7
Chronic facial pain, such as trigeminal neuralgia, is attributed to a malfunction of the trigeminal nerve, causing increased firing of neurons as well as an impairment of the inhibitory mechanisms that control activity in the trigeminal nucleus. The increased neuronal activity results in the perception of pain.14 It has been reported that the injection of BTX results in normalization of muscle spindle activity and the decompression of neurons of the muscular and vascular tissue.14
The successful role of BTX in the management of migraines has been demonstrated in several clinical trials.15,16,17 One suggested mechanism for this is that the BTX reduces the frequency and severity of pericranial muscle contractions that contribute to the migraine activation process.15 Common medications currently used to treat migraines are known to cause a number of side-effects, including drowsiness and stomach upsets, a complication that is removed with the use of BTX injections. However, some research suggests that there is no muscle component involved, but it is thought that BTX works by inhibiting the protein that carries the message of pain to the brain, thus affecting the sensory system and providing relief.4,15
Temporomandibular disorder (TMD) is a term used to describe a group of conditions involving the temporomandibular joint (TMJ) and associated muscles. TMD commonly affects young adults (20–40 years) and females more than males. It has been estimated that around 25–30% of the population will undergo medical care for TMD symptoms during their lifetime.18 Symptoms can include trismus, myofacial pain, TMJ clicking, headaches and TMJ dislocation. Treatment modalities include analgesics, physiotherapy and surgical interventions such as arthroscopy. For patients who have not responded to conventional treatment approaches, BTX injections can provide a treatment that is minimally invasive, whilst still achieving the desired results. Modulation of symptoms in TMD is due to the inhibition of muscle activity with BTX injections, therefore reducing the muscle tone and relieving symptoms.19
Bruxism is commonly seen in patients presenting with TMD. The word ‘bruxism’ is derived from the Greek word ‘brychein’ and means ‘to grind or gnash the teeth’ and the process can be attributed to tooth wear, periodontal issues and muscle damage.7
Continuous contraction of the muscle fibres (as seen in the masticatory muscles associated with bruxism) can lead to spasm, which in turn can manifest as pain. Multiple studies have shown the efficacy of BTX injections into the masticatory muscles (for example, masseter and temporalis) in relieving these symptoms,20,21 and it has been shown to be an effective and safe means of intervention.22
Frey's syndrome (also known as ‘Gustatory sweating’) is characterized by episodes of flushing and sweating of the facial skin during salivary stimulation and mastication. The condition is seen most commonly in patients who have undergone parotid surgery (for example, total parotidectomy) and is thought to be due to random regeneration of traumatized nerve fibres, usually innervating the parotid gland (likely auriculotemporal nerve fibres). The fibres damaged during surgery lose their parotid targets and so reorganize to innervate the sweat glands of the overlying skin, causing salivary secretion during eating.
Many therapeutic approaches to managing Frey's syndrome have been trialled over the years. Medical therapies, such as anti-cholinergic drugs, have not been well tolerated and surgical therapies are considered to be disproportionate to symptomatology.7
The use of localized BTX injections for the treatment of Frey's syndrome, into the region of gustatory sweating, was first described in 199523 and is now a well-recognized treatment modality for the condition (Figure 4). Many patients can remain symptom free for around six months24,25 and repeated administration has been shown to reduce the extent of the affected area.26
Sialorrhoea is commonly seen in neurological disorders such as Parkinson's Disease and Cerebral Palsy, as well as in patients with salivary fistulas and sialadenitis,27 and can have a profound negative effect on a patient's quality of life. Glandular secretions are modulated by acetylcholine, and so BTX injection into salivary glands can inhibit hypersalivation. This has been highlighted in multiple clinical trials, which have shown effects lasting 3–6 months without major adverse complications.28,29,30 In these cases, BTX injections depress the parasympathetic-dependant secretory function, not affecting the basal flow rate, which is maintained by the adrenergic pathway, in turn avoiding the risk of xerostomia.27,31
The use of Botulinum toxin in clinical treatments is both well established and safe.32,33 It has been reported that the therapeutic margin is 15:1,34 with safety closely reviewed and monitored by European regulatory agencies.35 There has been a paucity of evidence within the literature to document medical complications resulting from the administration of BTX, demonstrating its high safety profile.33
The most common side-effects following administration of BTX are localized and reversible.33 They are pain at the site of injection, closely followed by excessive weakness of the target muscle, or weakness of the surrounding anatomy.35 This can also include localized infection, swelling and inflammation around the side of the injection.7 When used in the head and neck region, this can present as an asymmetric smile or a difficulty to swallow if used intra-orally. There have been no urticarial or life-threatening allergies documented when facial BTX has been administered.33 However, BTX is contra-indicated in the presence of conditions, including Myasthenia Gravis and Eaton-Lambert syndrome, where the circulating levels of acetylcholine esterase are reduced in the synapse. It is also not used in patients with muscular dystrophy or multiple sclerosis.7
Registered dentists in the United Kingdom are permitted, under Section 58(2) of the Medicines Act, to prescribe, dispense and administer Botulinum toxin.36 In addition, the Dental Quality Assurance Commission (DQAC) states that general dentists are clinically allowed to use Botulinum toxin1 and the GDC provides specific guidance for dentists on the prescription of Botulinum toxin.37
Administration of Botulinum toxin for any dental or medical procedure requires fully informed consent from patients. Administrators need to be fully trained and skilled in the technique and have sound anatomical knowledge. Suitable indemnity is required with accurate and comprehensive documentation of all procedures. In accordance with GDC Standards for Dental Professionals, it is vital to act and perform treatment with Botulinum toxin within your scope of practice, which includes a thorough understanding of the complications of Botulinum toxin use and how to manage these.36
It is clear that BTX has many effective uses within dentistry, with increasing popular demand for its use in both medical and aesthetic applications. With continued development of the pharmacological research, combined with increasing FDA approvals, it is anticipated that BTX will be utilized further in both primary and secondary care. However, it is essential that clinicians who wish to carry out treatments using BTX have obtained the relevant training. The future of Botulinum toxin as a primary treatment or useful adjunct for many orofacial conditions is positive, and complements its most popular current application in facial aesthetics.
