TABLE 3.

Clinical studies of oral microbiota related to T2D.

No	Studies	Outcomes	References
1	This is a case-controlled study comparing the salivary microbiome of people with and without T2D and its relation to obesity status	• Patients with T2D have a decreased alpha diversity compared to the non-T2D • The Veillonella and Lactobacillus genera abundance increases in T2D patients • The Tannerella and Dialister genera decrease in T2D patients • Saliva type 1, which has a lower diversity and higher proportion of Streptococcus, Rothia, and Veillonella, was more common in T2D patients • Saliva type 3, which has a higher proportion of Neisseria and Porphyromonas, was more common in non-T2D patients	Shaalan et al. (2022)
2	A cross-sectional and case-controlled study comparing the oral microbiome characteristics in normoglycemic, pre-diabetes, and type 2 diabetes	- Microbiome diversity is reduced in patients with prediabetes and diabetes compared to non-diabetes patients. Diabetes patients have the lowest diversity of microbiome - The decrease in diversity in diabetic patients is attributed to an increase in pathogenic species. In diabetic patients, 38.5% of the bacteria are pathogenic, and no probiotic bacteria are present - Pathogenic bacteria identified in pre-diabetic and T2D groups include Staphylococcus warneri, Leptothrix sp., and Streptococcus downei	Saeb et al. (2019)
3	The analysis of saliva microbiomes in patients with or without diabetes undergoing uncovering procedures following implant placement	- No significant difference in alpha diversity was found between the two groups - Significant differences were only observed in the family Corynebacteriaceae and the genus Corynebacterium, both of which were more abundant in the non-diabetic group	Lee et al. (2022)
4	A cross-sectional observational study was conducted to review the composition of saliva microbiomes in diabetic patients and healthy volunteers	- Bacteroidetes, Proteobacteria, and Firmicutes are the most abundant phyla in both the diabetes and non-diabetes groups - Saliva from diabetic patients contains more Bacteroidetes and fewer Proteobacteria compared to non-diabetic individuals - There is a significant increase in the genera Prevotella, Porphyromonas, Veillonella, Leptotrichia, Lactobacillus, and Streptococcus in the diabetes group compared to the non-diabetes group - Genera Neisseria and Capnocytophaga are significantly higher in the non-diabetes group compared to diabetes	Agarwal et al. (2024)
5	Comparing salivary microbiome of 25 T2D patiens to 25 healthy volunteers	- There’s no difference in alpha and beta diversity between T2D and healthy gorup - Betaproteobacteria were significantly higher in T2D group - Deltaproteobacteria, Spirochaetes, Mollicutes, and Synergistia were significantly higher in healthy group	Almeida-Santos et al. (2021)