DIABETES-ASSOCIATED SALIVARY CHANGES AND THEIR IMPACT ON THE SUPRAGINGIVAL MICROBIOME

Abstract

Objective: To examine the biological mechanisms linking type 2 diabetes mellitus to increased dental caries risk, with emphasis on salivary sugar dysregulation and microbiome alterations.

Methods: A narrative review was conducted using experimental, clinical, and microbiome studies investigating the relationship between hyperglycaemia, salivary composition, and cariogenic biofilm development. Evidence was synthesized to clarify mechanistic pathways and clinical implications.

Results: Individuals with type 2 diabetes consistently demonstrate higher caries prevalence compared with non-diabetic controls. Emerging evidence indicates that chronic hyperglycaemia promotes the diffusion of circulating sugars, particularly glucose and fructose, into saliva. This metabolic shift increases substrate availability for supragingival biofilms and favours acidogenic and aciduric species. Studies using metabolomic profiling and microbial sequencing have shown enrichment of cariogenic bacteria, especially Streptococcus mutans, alongside reduction of health-associated species such as Streptococcus sanguinis. These ecological changes enhance glycolytic activity and acid production, contributing to enamel demineralization. Importantly, improved glycaemic control appears to partially reverse salivary sugar elevation and microbial dysbiosis, suggesting a modifiable pathway linking systemic metabolic status and oral disease risk.

Conclusion: Type 2 diabetes contributes to a more cariogenic oral environment through hyperglycaemia-driven alterations in salivary sugars and microbiome composition. Integrating metabolic control with preventive dental strategies may be essential to reduce caries burden in this population. Further longitudinal and interventional studies are needed to strengthen causal inference.