Epidemiology of research for temporomandibular disorders

A systematic review was performed in response to a request by the National Institute of Dental Research to evaluate in broad terms the strength of evidence regarding therapy for temporomandibular disorders (TMD). This report describes the epidemiology of research for TMD in broad terms indicating the total number of citations, the proportion related to therapy, and the distribution according to study design and language or country of origin. Medline and hand searching of article bibliographies and of selected journals produced the set of citations evaluated. From 1980 to 1992, there were more than 4,000 references to TMD, of which about 1,200 regarded therapy. Forty-one percent of the 1,200 references were classified as reviews and only 15% were clinical studies. Less than 5% (n = 51) were randomized controlled trials. This review identified a vast amount of literature on TMD with articles published in several different languages, indicating a worldwide interest in this problem. Because assimilation of this literature cannot be expected of the average practitioner treating patients who have TMD, or of most researchers in this area, it is likely not being used to its maximum potential. The literature on therapy for TMD consists primarily of uncontrolled observations of patients such as uncontrolled clinical trials, case series, case reports, and simple descriptions of techniques. It is generally agreed that such uncontrolled observations, while contributing to knowledge about therapy of TMD, are subject to considerable bias and thus difficult to interpret. If treatment of TMD is going to follow the trend in medicine to base patient-care decisions on evidence rather than expert opinion or pathophysiologic rationales, then more rigorously controlled clinical trials of most therapies will be necessary.