Although splints are used routinely in treating TMD, the mechanism of splint action has been considered unknown. This presentation, by using both systemic review of the literature and current research, will propose a mechanism of splint action for arthrogenous TMDs related to reducing intra articular pressures. An algorithm for splint design identified with RDC/TMD for myogenous diagnoses, disc displacements, and inflammatory joint disease will be proposed. Controversies will be discussed.