The further development of the principles of functional diagnostics also concerns the inclusion and integration of the issues in this dentistry sector with those of other medical sectors such as orthopaedic or psychosomatic medicine. Some scientific studies are now available that underscore the significance of appropriate tests for identifying any existing co-factors from these sectors of medicine. The list of service items contained in the German Dental Fee Schedule (GOZ) were hardly altered with regard to functional diagnostics by the GOZ fee reform in 2012, so that they differ very little from the previous version of 1988. Consequently, in this regard the GOZ is outdated, and since dentists in Germany are required by law to practice dentistry according to the current state of science, they cannot do so based solely on the service items listed in the GOZ. The legislator is aware of this problem and has, therefore, included the possibility in the new GOZ of invoicing those dental services not listed therein as independent service items according to the type of service, cost, and time input involved as well as the degree of difficulty of comparable services (referred to as "analogous services"). With reference to the example of tests for the determination of orthopaedic co-factors relating to a dysfunction of the stomatognathic system, this article describes the legal and functional background to the GOZ fees, and the consequences for their implementation in clinical practice. Keywords: temporomandibular dysfunction (TMD), tests for determining orthopaedic co-factors, clinical functional analysis, Dental Fee Schedule (GOZ), analogous billing