This paper reviews the effectiveness of occlusal splints on specific symptoms that are often associated with TM disorders. The research has shown the clicking TMJ is sometimes helped but not cured by the traditional stabilization interocclusal appliance and that TMJ clicking is the least responsive to treatment. Questions have been raised about the need to specifically treat the clicking joint; more research on this issue is necessary. Painful TMJs have been shown to respond to occlusal appliance therapy, but questions still exist about the effectiveness of interocclusal appliances for this symptom. There is little scientific proof available about the ability of splints to effectively slow down or reverse degenerative TMJ changes that are evident on radiographs. Masticatory muscle pain is by far the symptom that has the best experimental evidence to support occlusal splints as a highly effective method of treatment. These changes are probably mediated via an alteration in the patient's muscle activity patterns. Those patients with more severe symptoms are less likely to be helped with splints as a sole treatment modality. The effect of occlusal appliances in muscle trismus has been discussed but not effectively evaluated in the literature. Occlusal splints have been shown to have a distinct influence on improving mandibular muscle coordination. Inter-occlusal splints are a commonly used method of controlling attrition and adverse tooth loading, and few questions have been raised in the literature about this therapeutic application.