Botox Injection and temporomandibular disorders
Temporomandibular disorders (TMD) refer to the syndromes associated with the abnormalities of masticatory system. This article provides a detailed discussion about myofascial pain.
Myofascial pain disorders represent a significant portion of mandibular and facial pain. The mechanism underlying the etiology of myofascial pain is as yet unknown. Possible mechanisms that have been reported include neurologic, myogenous or psychologic disorders. Among them, hyperactive skeletal muscle bands and trigger points resulting in diffuse pain in masticatory muscles is the most widely accepted theory. Hyperactive trigger points can be caused from trauma, muscle strains or overuse injury.
Myofascial pain disorders are most commonly seen in adults aged 20-40, and the prevalence is higher among female than male. Signs of myofascial pain disorders usually accompany signs of TMJ internal derangement. The predilection sites include masseter muscles on the cheeks, temporalis muscles on the temples, sternocleidomastoid muscles (SCM) along the side of the neck and pterygoid muslces connected between the mandible and cranial bone. Muscle pain at the temples usually accompanies migraine.
Treatment of myofascial pain disorders (MPD) mainly involves in suppression and stabilization of the hyperactive skeletal muscle bands. Conservative treatment options at early stage of MPD include hot compress, physical therapy (e.g. massage and infrared therapy), medications and occlusal splint. Other options been reported include acupuncture and trigger point injection.
Botulinum toxin (Botox) has been used to treat a variety of neuromuscular syndromes, e.g. chronic migraine, cervical dystonia and strabismus. Botox injection inhibits muscle contraction by blocking the release of acetylcholine from presynaptic nerve terminals. In addition, some studies revealed that botox had inhibitory property on the production of some neurotransmitters from peripheral receptors, e.g. substance P, glutamate, calcitonin gene-related peptide (CGRP), particularly against local muscle spasms or contractions, as well as local antinociceptive and analgesic properties. Therefore in recent years more and more attentions have been focused on the application of botox on treating myofascial pain disorders.
Many clinical studies showed that botox could effectively reduce the intensity, frequency and duration of pain in patients with myofascial pain disorders (NivMor, 2015). Freund et al. investing the effect of botox injection into masseter and temporal muscles on 46 patients with myofascial pain disorders found that the pain of the patients was greatly improved. Another study investing botox injection on 100 patients with myofascial pain disorders showed that 70% of the patients got improved in their pain syndromes with an average of above 50% improvement in the pain frequency and intensity (Bentsianov, 2004).
The above-mentioned researches confirmed that the positive effect of botox injection on treating myofascial pain disorders. For patients showing persistent myofascial pain with poor response to conservative treatment (e.g. long-term wearing occlusal splint), botox injection remains the best alternative second-line treatment option (Sidebottom, 2012; Fallab, 2012).。
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