A group of 248 randomly selected high school girls, aged 15-16 years, completed a questionnaire and were examined clinically with regard to various oral habits and signs and symptoms of temporomandibular disorders (TMD). Common habits reported in the literature, such as gum chewing, nail biting, biting foreign objects, clenching and bruxism, eating seeds and crushing ice, as well as two less reported habits, 'jaw play' and continuous arm leaning, were evaluated. The most outstanding finding was the high prevalence and intensity of gum chewing among our study group: 92% of the girls chewed daily and 48% chewed gum for more than 3 h a day (intensive gum chewing). Statistically significant associations were found between intensive gum chewing and muscle sensitivity (P<0.001) and joint noises (P<0. 05), and between crushing ice and muscle sensitivity to palpation (P<0.005). A positive association was found between 'jaw play' and joint disturbances: reported joint noises (P<0.01), catching of the joint (P<0.01) and joint tension (P<0.001). A positive association was also found between arm leaning and reported joint noises (P<0. 05), catching (P<0.05), and joint tension (P<0.005). There was no association between the presence of bruxism and muscle sensitivity to palpation or joint disturbances. The potential harmful effects of intensive gum chewing, 'jaw play', continuous arm leaning and ice crushing are presented in this study. In light of these findings, the professional community should address these habits with proper data gathering, examination and consultation.

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Jaw play was the most detrimental habit in TMD; intensive gum chewing was a potentially contributing factor for joint noises and pain. Oral parafunctions (except chewing gum) were significantly associated between themselves and suggest a behavioural pattern of "jaw hyperactivity".

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A group of 248 girls, aged 15-16 years, were randomly selected and examined both clinically and by questionnaire with regard to the signs and symptoms of temporomandibular disorders (TMD), generalized joint laxity (GJL), range of mandibular opening, temporomandibular joint (TMJ) hypermobility and presence of oral parafunctions. The prevalence of GJL was 43% and that of TMJ hypermobility (TMJH) was 27.3%. A significant, albeit weak, correlation was found between the two. In the presence of joint click, both active and passive opening were significantly larger. When either muscle or joint sensitivity to palpation was present, the difference between the active and passive range of mouth opening increased significantly. The presence of reported clicks was negatively associated with GJL. This association was not valid in the presence of parafunction. Some of the signs and symptoms of TMD affected the range of mouth opening. In the presence of joint clicks, the mean active and passive mandibular opening were significantly larger. In the presence of joint and muscle sensitivity to palpation, the difference between passive and active mouth opening was larger. This was possibly because of the effect of pain on the full active range of opening, which was invalid in the registration of the passive mandibular opening. GJL, when present, did not seem to jeopardize the health of the stomatognathic system as expressed in the signs and symptoms of TMD. There was a negative association between GJL and the presence of reported joint clicks and catch. When a parafunction was present in addition to GJL, this association was invalid but not reversed, as has been previously reported.