The present study was performed on media personnel who could be considered as under sustained pressure at work due to intense on-going technological and organizational changes. The study formed part of a comprehensive investigation on shift work and its sleep/awake consequences, and it focused on irregular shift work, which, however, did not emerge as a significant factor in itself. This was a finding that accords with results from earlier studies derived from the present data base [15–17].
Unfortunately, despite several postal reminders, we resulted in a low response rate in the regular day work group. This was partly expected as the study was transparently targeted to examine the health effects of irregular shift work. The invited subjects and respondents in both shift work and day work groups were similar as regards gender and age, which, on the other hand, may modestly suggest that also the day work group could be representative. Nevertheless, due to the uneven response rates the present study may have failed in detecting the actual differences between these two groups.
However, we studied the associations of self-reported bruxism with perceived insomnia symptoms and insufficient sleep using multivariate models in which some confounding factors (viz., restless legs syndrome, snoring, gender, age, and dissatisfaction) relative to sleep quality were simultaneously controlled. Bearing in mind the lower response rate in the day work group, the models were also tested excluding the work group variable, which did not markedly change the effects of the other independent variables. Thus, the work group variable was not considered to be a confounding factor in the models, and further, it was eventually included in the present analyses not to reduce the statistical power.
As the major interest was in self-reported bruxism, the main findings were that frequent bruxism was significantly associated with perceived insomnia symptoms (except EMA) and insufficient sleep. These associations also held in the multivariate analyses. The results may imply a stressful work environment or work dissatisfaction, as discussed earlier [15–17]. The statistically non-significant relationship found between bruxism and EMA, the latter often reportedly associated with depressive mood , has also been suggested to be due to the overall low psychological dysfunction found in the present non-patient population .
Using questionnaires, as in the present study, may cause difficulties in defining the actual prevalence of bruxism; it may even have been more common among populations but not reported as a behaviour by individuals because of its potential subconscious nature. Or, on the other hand, reporting of bruxism may be influenced by negative affectivity, and individuals with subjective distress may be more likely to perceive, overreact to and complain about their sensations. In the present study bruxism was defined as a subjective perception of tooth grinding or clenching and the definition includes both sleep and awake parafunctions. This also means that sleep and awake bruxism cannot be separated here.
Studies have suggested that stress experience and psychosocial factors may play an important role in the etiology of bruxism . In contrast, evidence also exists that both experienced and anticipated stress associate with awake clenching but would be unrelated to sleep-bruxism recorded with ambulatory devices [23, 24]. Polysomnographic studies have revealed, however, that bruxism appears concomitantly with the transient arousal response and has been shown to associate with both sleep quality and sleep architecture [12, 14, 25]. On the other hand, it is well accepted that stress experiences at work are linked to disturbed sleep and fatigue [26, 27]. Thus, if perceived stress or dissatisfaction affect sleep, it could be assumed that they may concomitantly precipitate or amplify bruxism. Further, fatique and pain in the masticatory muscles may be a repercussion of this process.
As regards insomnia symptoms both DIS and DS were found to be markedly more common than previously reported in Finland . On the other hand, the presence of EMA did not differ from that reported in the general population. Also, female gender was overall associated with insomnia symptoms, which is in line with previous epidemiologic findings outside Finland [28–30]. In the present study, age had diverse effects; those ≥ 45 years more often had DS and EMA but yet the younger subjects were more likely to report insufficient sleep complaints. As regards DS this has not been the case in the general population, but it accords with the results found elsewhere. It is noteworthy that DS, also the most significant factor associated with bruxism, emerged as a major sleep disturbance affecting nearly half of subjects in the present non-patient population.
In the multivariate analyses, despite the several associations found cross-sectionally, RLS was significantly associated only with DIS. Snoring, in turn, which was bivariately associated only with DS, was multivariately associated with both DS and SLD. These findings seem logical and they also underscore that neurological or physical factors should be borne in mind when diagnosing and treating insomnia and insufficient sleep problems. Especially in the case of RLS a substantial under-recognition may exist [31–33].
The phenomenon of bruxism may well be genetic in origin, affected psychosocially or pathophysiologically, but is most likely centrally regulated . Yet, despite the increasing number of studies on bruxism, it remains unclear why self-perceived bruxism and polysomnographically or clinically detected bruxism seem to be poorly associated and do not share their etiology. Based on the present study, however, it may be possible to conclude that self-reported bruxism indicates sleep problems and their adherent awake consequences. Also, the found independently detrimental effect of dissatisfaction on sleep should not be ignored.