Low-level laser and transcutaneous electrical nerve stimulation on salivary glands impact type 2 diabetes mellitus oral microbiome: an interim analysis of a randomized trial

Diabetes Mellitus (DM) can lead to significant reduction of saliva production, which increases the risk of oral diseases. Managing reduced salivary flow becomes indispensable for restoring microbial balance in this condition. This study aimed to investigate the effects of physical stimulation methods on salivary secretion rate and microbiome composition in individuals with type 2 DM (T2DM) having reduced salivary flow using an exploratory interim analysis of a randomized clinical trial.

Methods Eight individuals provided a total of 15 stimulated or rest saliva samples and were randomly assigned to the following groups: low-level laser therapy (LLLT) (G1), transcutaneous electrical nerve stimulation (TENS)(G2), and a combination of both methods(G3), administered twice a week over a span of 10 sessions. Salivary flow was evaluated at three time points: recruitment, before the 1st session (baseline) and after the 10th session. Subjective dry mouth was evaluated using the TESS scale at baseline and after the final session. DNA was extracted from whole saliva immediately before treatment (baseline) and after the final stimulation session, 16 S rRNA gene amplified and sequenced (Illumina MiSeq).

Results N = 7 individuals showed improvement in stimulated salivary flow (SSF), achieving or maintaining normal range (SSF > 0.7 ml/min). Bacterial diversity was significantly higher in saliva after stimuli with laser(G1) when compared to TENS(G2). The relative abundance of Firmicutes and Fusobacteriota increased after all treatments, while Actinobacteriota and Proteobacteria decreased. The abundance of minority taxa was reduced after stimulation.

Conclusion This exploratory study provides initial indications that physical stimulation may help manage T2DM-related reduced salivary flow and could be associated with subtle changes in low-abundance taxa suggesting a potential “clearance” effect. These preliminary observations require confirmation through larger, long-term studies.

Trial registration number RBR-3tqv8r3. Date of registration: 13th April 2023.