The teeth provide precise skeleto-motor influences for the stomatognathic system. This unique guidance mechanism characterizes each individual's chewing pattern. It controls the activity of jaw muscles to ensure that appropriate tooth contacts within the limits of existing tooth relationships occur at the end of each chewing cycle. This acts as a means of re-setting the neuromuscular system in anticipation of the next jaw opening movement. The absence of stable centric occlusion at the end point of each chewing cycle alters neuromuscular co-ordination and predisposes to muscle dysfunction. Tooth and jaw or craniomandibular relationships are associated with craniocervical relationships and especially tongue posture. This is also directly influenced by the need for airway maintenance as the predominant influence on tongue-muscle function. The susceptibility to pain and dysfunction is further influenced by individual stereognathic sensitivity or the variable awareness of tooth contour and tooth contacts. These special features are present within the framework of the psycho-physiological and psycho-social significance of the face and mouth, which directly bears on the individual response to and appreciation of pain and dysfunction. Tooth guidance also influences condyle-disc function. Anterior and posterior teeth provide primary and secondary lateral guidance in function, directing the jaw into centric occlusion. If this guidance tends to direct the jaw posteriorly along distal, rather than mesial tooth inclines, it restricts the antero-posterior 'function' of jaw movement at tooth contact. This predisposes to condyle-disc dysfunction and the development of internal derangements, by increasing the likelihood of the posterior thick band of the disc being displaced anteriorly and the condyle posteriorly.(ABSTRACT TRUNCATED AT 250 WORDS)