Psychological Distress: A Mediating Factor in the Relationship Between Sleep Bruxism and Tobacco Smoking

Background: Sleep bruxism (SB) is defined as a masticatory muscle activity during sleep characterised by a multifactorial aetiology. Tobacco smoking and psychological status are considered predisposing factors for SB, but their mutual interaction remains unclear. Objective: To investigate the relationship between self-report SB, tobacco smoking, and psychological status, adopting a multiple-variable model in a sample of healthy young adults. Methods: A sample of 150 individuals (Female = 62%; mean age (±SD) = 23.3 (±3.4) years) completed a questionnaire to assess self-reported SB, tobacco smoking, and psychological distress. Self-reported SB was assessed according to the Subject-Based Assessment strategy recommended in the ‘Standardized Tool for the Assessment of Bruxism’ (STAB). Psychological distress was evaluated using the four-item Patient Health Questionnaire-4 (PHQ-4) for anxiety and depression. Tobacco smoking was assessed by four questions included in the Global Adult Tobacco Smoking (GATS) questionnaire. Spearman's rank correlation, ordinal regression, and mediation analysis were used to examine the relationship between SB, psychological distress, and smoking-related variables. Results: Significant positive correlations between SB and psychological distress (r = 0.350, p < 0.001) and between SB and n° cigarettes/day (r = 0.196 p < 0.05) emerged. Psychological distress positively mediated this relationship between tobacco smoking and SB, with an indirect effect of 0.065 (C.I. = 0.108–0.313; p value < 0.05). Psychological distress showed a positive predictive effect for SB (OR = 1.23, C.I. = 0.071–0.345, p < 0.05), while no significant associations with smoking variables were found. Conclusions: Within the limitation of this study, tobacco smoking does not seem to be directly correlated with sleep bruxism. Psychological distress could play the role as a mediating factor in this relationship.