The aim of dental treatment is to maintain the teeth and periodontium in a healthy condition, and to restore or replace teeth to achieve acceptable aesthetics, speech, and mastication. Dental treatment also aims to maintain the health of the entire stomatognathic system, i.e. temporomandibular joints, orofacial muscles and physiognomy, as a prerequisite for acceptable oral function. Aesthetical, social and psychological demands have to be satisfied as well. Factors other than merely mechanical aspects are involved in the maintenance and rehabilitation of oral function, and are important in mastication in 8 particular and in oral well-being in general. The prosthodontist has to take into account that these factors will determine the subjective need for prosthetic treatment, probably more than other objective criteria.