Salivary Flow Rate, pH, and Buffer Capacity in the Individuals with Obesity and Overweight; A Meta-Analysis

Background: Weight in individuals can affect the saliva structure, which has an essential role in caries prevention. Aim: This meta-analysis aimed to compare individuals with obesity (OB)/overweight (OW) and normal weight (NW) in terms of salivary flow rate (SFR), salivary pH (SpH), salivary buffer capacity (SBC). Materials and Methods: After electronic databases (Web of Science, PubMed, Scopus, Cochrane Library, and Open Grey databases) were screened, studies were selected depending on inclusion criteria. The Joanna Briggs Institute Critical Appraisal Checklist was used to assess the risk of bias in individual studies. Mean differences (MD) were used to measure the effect estimates in the comparisons of OB vs NW, OW vs NW, and OB+OW vs NW. Additional analyzes such as subgroup, moderator, sensitivity, and grade were also performed. Results: 24 studies and 2072 participants (SFR: 748 OB, 896 NW, SpH: 137 OB, 166 NW, SBC: 62 OB, 63 NW) were included in the quantitative synthesis. Significantly lower SFR was found in the group with OB compared to NW when saliva was stimulated (MD = -0.21, 95% CI [-0.30, -0.12], P < 0.001), but no significance was obtained when saliva was unstimulated (MD = -0.02, 95% CI [-0.11, 0.06], P = 0.55). No significant difference was found in the group with OB compared to NW in SpH (MD = -0.07, 95% CI [-0.26,0.12], P = 0.48) and SBC (MD = -1.10, 95% CI [-2.29,0.09], P = 0.07). Conclusions: SFR significantly decreases in individuals with OB, notably when saliva is stimulated. Besides, the decrease in SFR is much more prominent in adolescence and adulthood than in childhood. Furthermore, the increase in the severity of OB causes a much greater decrease in SFR. However, regarding SpH and SBC, no significant association exists.