In more than one half of patients with burning mouth syndrome, the onset of pain is spontaneous, with no identifiable precipitating factor. Approximately one third of patients relate time of onset to a dental procedure, recent illness or medication course (including antibiotic therapy). Regardless of the nature of pain onset, once the oral burning starts, it often persists for many years.

The burning sensation often occurs in more than one oral site, with the anterior two thirds of the tongue, the anterior hard palate and the mucosa of the lower lip most frequently involved. Facial skin is not usually affected. No correlation has been noted between the oral sites that are affected and the course of the disorder or the response to treatment.

In many patients with the syndrome, pain is absent during the night but occurs at a mild to moderate level by middle to late morning. The burning may progressively increase throughout the day, reaching its greatest intensity by late afternoon and into early evening. Patients often report that the pain interferes with their ability to fall asleep. Perhaps because of sleep disturbances, constant pain, or both, patients with oral burning pain often have mood changes, including irritability, anxiety and depression. Earlier studies frequently minimized the pain of burning mouth syndrome, but more recent studies have reported that the pain ranges from moderate to severe and is similar in intensity to toothache pain.

Little information is available on the natural course of burning mouth syndrome. Spontaneous partial recovery within six to seven years after onset has been reported in up to two thirds of patients, with recovery often preceded by a change from constant to episodic burning. No clinical factors predicting recovery have been noted.

Most studies have found that oral burning is frequently accompanied by other symptoms, including dry mouth and altered taste. Alterations in taste occur in as many as two thirds of patients and often include complaints of persistent tastes (bitter, metallic, or both) or changes in the intensity of taste perception. Dysgeusic tastes accompanying oral burning are often reduced by stimulation with food. In contrast, application of a topical anesthetic may increase oral burning while decreasing dysgeusic tastes.

Orofacial pain of muscular origin is often referred to as myofacial pain. The current conservative treatment approach includes the use of nonsteroidal anti-inflammatory medications, soft diet, and occlusal splint. Other medications such as muscle relaxants and tricyclic antidepressants have been used. Some clinicians advocate the use of other modalities such as massage therapy, ultrasound therapy, and transcutaneous electric nerve stimulation. More than 80% of patients respond to conservative therapy.¹³

For those patients who are refractory to these treatments and continue to suffer significant pain and dysfunction, treatment with BTX has been proposed. As mentioned previously, patients with masseteric hypertrophy and pain often respond well to BTX A administration to the affected muscles. In a randomized, blinded, placebo-controlled study by Von Linden, et al⁷, 90 patients with chronic facial pain were treated (60 BTX A, 30 placebo). Patients received on average 35 units of BTX A to affected muscles (masseter, temporalis, or medial pterygtoid), and 0.9% normal saline was used as a control. The data indicated that 91% of those who received BTX A reported improvement, with a significant mean reduction of approximately 3.2 on the visual analog pain scale (VAS 0 to 10).

It is believed that BTX A hinders trigeminal nerve activity not only by preventing the release of acetylcholine but also preventing the release of substance P. Substance P is a potent neurotransmitter that plays a role during neurological inflammation.⁷ Furthermore, BTX A therapy can indirectly alleviate pain of arthrogenic origin. This is achieved with the prolonged “joint-sparing” effect of diminished loading secondary to the decreased ability of the musculature to affect joint loading.⁸

A study by Freund, et al⁹ also supports the effectiveness of BTX A in the reduction of myogenic pain associated with the TMJ. Forty-six patients with TMD were treated with a total dose of 150 units of BTX A (50 units per masseter and 25 units per temporalis). During the following 8 weeks these patients had a mean 3-point reduction in the 0 to 10 VAS pain score. There were no controls in this study.⁹

A study by Nixdorf, et al10 of 15 patients (10 completed the study) examined the use of BTX A for chronic myogenous orofacial pain. This report did not show a statistically significant improvement in the group that received BTX A versus normal saline. In the discussion, they acknowledged the small number of patients in the study.¹⁰