Review Bruxism is mainly regulated centrally, not peripherally F . LOBBEZOO & M. NAEIJE Section of Craniomandibular Disorders, Department of Oral Function,Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands SUMMARY SUMMARY Bruxism is a controversial phenomenon. Both its de®nition and the diagnostic procedure contribute to the fact that the literature about the aetiology of this disorder is dif®cult to interpret. There is, however, consensus about the multifactor- ial nature of the aetiology. Besides peripheral (mor- phological) factors, central (pathophysiological and psychological) factors can be distinguished. In the past, morphological factors, like occlusal discrepan- cies and the anatomy of the bony structures of the orofacial region, have been considered the main causative factors for bruxism. Nowadays, these fac- tors play only a small role, if any. Recent focus is more on the pathophysiological factors. For exam- ple, bruxism has been suggested to be part of a sleep arousal response. In addition, bruxism appears to be modulated by various neurotransmitters in the central nervous system. More speci®cally, distur- bances in the central dopaminergic system have been linked to bruxism. Further, factors like smo- king, alcohol, drugs, diseases and trauma may be involved in the bruxism aetiology. Psychological factors like stress and personality are frequently mentioned in relation to bruxism as well. However, research to these factors comes to equivocal results and needs further attention. Taken all evidence together, bruxism appears to be mainly regulated centrally, not peripherally. KEYWORDS KEYWORDS : bruxism, aetiology, morphology, patho- physiology, psychology, review Introduction The number of studies that aim to unravel the mech- anisms behind bruxism is increasing rapidly. Neverthe- less, this clinical problem (Lavigne et al., 1999) remains dif®cult to grasp and controversial. For example, there is still no agreement regardingthe de®nition and diagnosis of bruxism (Lavigne & Manzini, 2000).As a consequence, the available articles on the aetiology of bruxism are dif®cult to compare and therefore hard to interpret unequivocally. The interpretationof the literature is further hampered by the fact that the effects of factors like gender and race on the prevalence of the disorder are not yet clari®ed (Lavigne et al., 1995). This makes the generalization of certain ®ndings dif®- cult. Moreover, insight into study design has improved considerablyduring the last decade.For instance, control subjectsare frequently absent in previous studiesand regularly, the phenomenon of interest, bruxism, was quanti®ed with indirect measures. Notwithstanding these dif®culties, many aetiological theories to explain bruxism have been formulated over the years. Although these theories are hard to con®rm or refute because of the controversial character of the disorder, most suggest a multifactorial aetiology (Attanasio,1997;Lobbezoo & Lavigne, 1997;Bader & Lavigne,2000; Lavigne & Manzini, 2000). Basically, two groups ofetiologicalfactors can be distinguished, viz., peripheral(morphological)factors and central (pathophysiological and psychological) factors. Below, both groups will be reviewed and the current view on their relative contribution to the aetiology of bruxism will be discussed. Some authors stress the importance to discriminate between sleep-related bruxism and bruxism during wakefulness, because both types may have a different aetiology (Ramfjord, 1961; Glaros, 1981; Rugh & Harlan,1988).In this review,bruxism willbe consid- ered the combination ofall parafunctionalclenching and grinding activities, exerted both during sleep and ã 2001 Blackwell Science Ltd 1085 Journal of Oral Rehabilitation 2001 28; 1085±1091