As the evidence base for functional diagnostics expands with continuous research and development, this area of dentistry is becoming more and more integrated and interwoven with other medical fields such as psychosomatics and orthopedics. By now, many scientific studies exist in which tests have demonstrated associations between potential co-factors from these medical specialties and temporomandibular dysfunction (TMD). Even after the reform in 2012 of the German Dental Fee Schedule (GOZ), there is almost no change in the list of functional diagnostic services included in the new GOZ compared to the previous version of 1988. While the German Dentistry Act obligates dentists to practice dentistry in Germany according to the current state of scientific knowledge, it is impossible for dentists to do so if they are limited solely to the services included in the outdated contents of the official GOZ. However, German legislators deliberately drafted the new GOZ so as to include provisions for dentists to charge fees for separate services not included in its catalog of services, according to the type, cost, time requirement, and degree of difficulty of comparable services ('analogous billing procedure'). This article explains the legal framework and professional background for the implementation of this practice as well as the consequences thereof based on the example of tests to identify psychological co-factors that contribute to functional disorders of the temporomandibular system. Keywords: temporomandibular disorder (TMD), tests for the identification of psychological co-factors, clinical functional analysis, German Dental Fee Schedule (GOZ), analogous billing procedure,