Exploring the relationship between sleep bruxism and saliva: A systematic review and meta-analysis

Sleep bruxism (SB) is defined as rhythmic masticatory muscle activity occurring during sleep. Evidence suggests that SB may be associated with alterations in salivary function; however, findings remain inconsistent across age groups. This study aimed to evaluate the relationship between SB and salivary flow and composition. A systematic search of PubMed®, Embase® and Web of Science was conducted to identify human studies reporting SB and saliva-related parameters. Twenty studies involving 4,543 participants were included. Risk of bias was assessed using the Risk of Bias Assessment tool for Non-randomized Studies (RoBANS-2), and certainty of evidence was appraised using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) framework. In pediatric populations, SB was frequently associated with sleep drooling, with a pooled prevalence of 77.4% and a significant association between SB and drooling (odds ratio (OR): 2.88, 95% confidence interval (CI): 1.53-5.42; I2 = 91%). In adults, 2 studies reported inconsistent findings regarding objectively measured salivary flow, and 1 study found an association with subjective xerostomia. A meta-analysis of 4 studies indicated elevated salivary cortisol in participants with SB (standardized mean difference (SMD): 0.86, 95% CI: 0.44-1.29), although studies using polysomnography for SB diagnosis found no significant differences. Results for chromogranin A (CgA) and α-amylase were heterogeneous. Overall, the available evidence, which was of very low certainty, suggests that SB is associated with hypersalivation in pediatric populations and with subjective oral dryness in adults, whereas associations with salivary biomarkers remain inconclusive. Future studies using standardized, age-specific protocols that combine objective SB diagnostic methods with controlled saliva sampling are warranted to clarify the underlying mechanisms and inform clinical management.