Commentary

This is a systematic review that attempts to evaluate the efficacy of various pharmacologic treatments for three different categories of oro-facial pain: temporomandibular muscle disorders (TMD-muscle), temporomandibular joint disorders (TMD-J) and burning mouth syndrome (BMS). The first two may have some overlap of diagnoses. The prevalence of TMD-arthritis and TMD-disc displacement is relatively low compared to TMD-muscle pain; however, these two joint sub-groups are commonly diagnosed in conjunction with TMD-muscle pain.1

BMS is an unrelated neuropathic disorder diagnosed with symptoms of oral mucosal burning and the exclusion of oral mucosal disease. BMS is most common in post-menopausal women, with prevalence rates in the general population varying between 0.1%-3.9%2 with a recent population-based study showing a prevalence of 0.11%.3

It is not clear in the review which diagnostic criteria were accepted for inclusion in any of the categories. There are research standards, the most recent being the Research Diagnostic Criteria (RDC) for Temporomandibular Disorders for the diagnosis and categorisation (muscle, disc displacement or arthritis) of temporomandibular disorders.4 Without standard diagnostic criteria, the nature and the severity of the conditions included are uncertain.

It should also be noted that patients with rheumatic disorders were excluded from this study, which could greatly affect the results on TMD-joint, as arthritis is one sub-category of this disorder. As for BMS, since the diagnosis is made by exclusion it is important to know which conditions were indeed excluded.

The studies included topical, local and systemic pharmacologic interventions, with varying doses and durations. Since the results were based on the combined effect of an individual agent, it is uncertain which aspect is responsible for the observed effects such as the agent, the delivery, the duration or the dose.

It was beneficial that this review only used visual analog scales (VAS) for outcome measures of pain reduction. Only five of the forty-one studies measured quality of life and found no effect on quality of life.

The use of the NMA offers the advantage of allowing comparison of multiple interventions in a single review. For the TMD-joint group, the included studies were not eligible for NMA, however the authors suggested there is evidence supporting the use of NSAIDs, and corticosteroid and hyaluronate injections. For the TMD-muscle group the NMA (eight studies) supports evidence of the pain-reducing effect of cyclobenzaprine (a muscle relaxant); however, there was only a three-week follow-up. For BMS, five studies were included in the NMA, and based on the authors' interpretation, it supports the pain-reducing effects of clonazepam (a benzodiazepine commonly used for neuropathic pain) and topical use of capsaicin (a substance found in chilli peppers that causes nerve desensitisation thereby reducing pain signals). Of the three clonazepam studies, two were topical and one was systemic, with varying frequencies and durations from two weeks to two months duration. Only one capsaicin study was included in the NMA, which also compared the use of alpha lipoic acid and lactoperoxidase, all of which showed statistically significant effect in pain reduction but no significant difference between groups. It is unclear how the superiority of capsaicin was established. In this review, with so few eligible studies, NMA may not be able to offer an advantage.

By far, the data in this review are insufficient to determine which pharmacologic interventions provide the best pain relief in any of these oro-facial pain conditions.

The range of duration of the individual studies (two weeks up to six months) may be too short to understand the effect on a chronic condition that may require long-term treatment. When studying therapeutic effects on a chronic pain condition, long-term follow-ups are needed.

Also evidence is lacking for short and long-term side effects, quality of life and cost.