Reasons for classification

Medical classification is the process of transforming descriptions of diagnoses and procedures into universal medical code. It is from these codes that data can be collected and analysed for the purpose of providing the hard evidence needed to determine whether TMJ surgery is effective in providing material benefit to patients. In other words, the hard evidence for TMJ surgery can only be secured with a universally recognized surgical classification of TMJ disorders.

Presently, there are 3 main classifications related to TMD; the Research Diagnostic Criteria (RDC) for TMD, the Wilkes Classification for TMJ internal derangement, and the most recent American Academy of Orofacial Pain (AAOFP) Classification of TMD. The RDC-TMD classification is the most widely used by TMD researchers who stress the importance of psychosocial dysfunction (Axis II) as opposed to physical disorders (Axis I) and come up with a wide variety of complex calculations that often have little bearing on clinical practice. The RDC-TMD has remained firmly embedded in the research world with little use in clinical practice.

The Wilkes classification is the most widely used classification that has been adopted by surgeons who treat TMJ disorders. Its widespread adoption is linked to its simplicity in describing escalating joint pathology in 5 stages, but it concentrates on only 2 disorders (internal derangement and osteoarthritis) and fails to include other TMJ disorders such as ankylosis and tumours which are covered by a host of other sub-classifications that will not be elaborated here.

The AAOFP classification of TMD has refocused its attention on articular disorders with a more widespread appreciation of joint disease, not confined to internal derangement, but also ankylosis, trauma and even developmental conditions of the TMJ are listed. The masticatory muscle disorders are listed simply as local, general and centrally mediated which reflects the poor understanding of extra-articular disorders related to TMD. While the AAOFP classification of TMD is a vast improvement on the cumbersome RDC-TMD, there is still a problem when it comes to data collection as the AAOFP classification does not allow for degree of disability which is quantifiable like the Wilkes Classification.

In 1994, Dolwick and Dimitroulis published a table which divided indications for TMJ surgery into relative and absolute. Relative indications were stipulated for common TMJ disorders such as internal derangement and osteoarthrosis, while absolute indications were reserved for less common TMJ disorders such as ankylosis and neoplasia of the TMJ. Surgical indications such as this only indicate when TMJ surgery should be considered, but does not stipulate what kind of surgery is required and for which disease.

New classification

In the development of a new classification, it is essential to purge the weaknesses and build on the strengths of previous classifications. Dozens of new medical classifications are introduced to the literature every year, but history has shown that only the simplest, such as the classic Le Fort classification for midface injuries, that are easy to remember and simple to understand are universally adopted. The criteria for the new classification are given in Table 1 . The purpose of this new classification ( Table 2 ) is to specify the role of TMJ surgery in all TMJ disorders in a graded fashion across a spectrum of 5 categories of escalating degrees of joint disease.