Abstract: For improving the functionality and bio-compatibility of dental appliances (2), a novel process is described for making a thermoplastic functional foil (1), from which such dental appliances (2) may be obtained by thermoforming the functional foil (1). A carrier liquid (9) containing an organic and preferably bio-based polymer (6) is enriched with an agent (7) and applied onto a solid thermoplastic core foil (13). After evaporating of a solvent contained in the carrier liquid (9), a uniform and highly homogenous functional coating (5) is obtained on the core foil (13). After thermoforming of the foil (1), the dental appliance (2) thus features an outer protective coating (5) offering enhanced functionality. Moreover, it is possible to reload the agent (7) into the coating (5) of the appliance (2) using a reload-liquid (23).