Couldnt find any (relatively recent) studies that looked at bacteria over multiple years, but some earlier ones (1&2), or shorter period ones(3), that touch on it (aswell as caries, as that is the prevalent subject)

https://pubmed.ncbi.nlm.nih.gov/2758793/

https://pubmed.ncbi.nlm.nih.gov/1810656/

https://www.frontiersin.org/journals/nutrition/articles/10.3...