Etiopathogenesis of parafunctional habits of the stomatognatic system

broad consensus does exist among main authors on the importance of
parafunctional habits in the etiopathogenesis of temporomandibular disorders
(TMD). Mechanisms through which an intense parafunctional activity determined a
pathological effect on the temporomandibular joints (TMJs) and their related
structures have still not been definitively clarified; nevertheless, before
investigating those mechanisms, it's useful to study predisposing, triggering
and/or worsening factors of parafunctions themselves. At present the theory, once
widely accepted, according to which occlusal interferences can trigger a muscular
hyperactivity through the activation of periodontal receptors, has lost a lot of
credit. Recently, the hypothesis that bruxism and other parafunctions have a
central etiology has become more and more accepted. In such a context, the role
of the psychic component assumes a strong relevance, particularly for its
relation with the limbic system, which is the part of the central nervous system
(CNS) that regulates emotions. Such a hypothesis is confirmed by clinical
practice, but it doesn't explain why some patients have reported a worsening of
parafunctional activities after occlusal adjustment. The aim of this study is to
investigate this issue through a critical review of the literature, indicating
how the 2 theories might be complementary for the development and worsening of a
parafunctional habit. From this review, despite the number of clinical opinions,
there emerges a lack of methodologically appropriate associative works and
controlled clinical trials which consent to clarify the effective importance of
psychic and/or occlusal factors in the etiopathogenesis of parafunctional habits.