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Recent results of randomized trials testing the efficacy of xylitol in caries prevention have been conflicting. This narrative review reveals the sources of discrepancy. The following databases were searched for the terms "xylitol" or "artificial sweeteners" restricted to the English language: PubMed,

Dental plaque may contain 1011 bacteria/mg and over 700 microbial species have been identified in the oral cavity. Microorganisms may gain access from the mouth into the circulation through decayed teeth, periodontal pockets and mucosal lesions. Frail edentulous persons are also susceptible to yeast infections if oral hygiene is poor. Oral infections have been suggested to pose detrimental effects to systemic health, in particular, cardiovascular diseases. Functional capacity and muscle strength may also be impaired by chronic mouth infections. These infections also seem to associate with all-cause mortality. Thus, oral infections need to be properly diagnosed, treated and prevented in elderly individuals. An additional problem in the aging population is medication that can often reduce saliva secretion and cause dry mouth. This further predisposes older adults to oral infections. Therefore, polypharmacy should be avoided whenever possible.

As the largest immune organ, human gut microbiome could influence the efficacy of immune checkpoint inhibitor therapy (ICI). However, identifying contributory microbes from over 35,000 species is virtually impossible and the identified microbes are not consistent among studies. The reason for the disparity may be that the microbes found in feces are markers of other factors that link immune response and microbiotas. Notably, gut microbiome is influenced by stool consistency, diet and other lifestyle factors. Therefore, the ICI and microbiotas relationship must be adjusted for potential confounders and analyzed longitudinally. Moreover, a recent study where 11 low-abundance commensal bacteria induced interferon-γ-producing CD8 T cells, challenges the validity of the abundance-oriented microbiotas investigations. This study also confirmed the hierarchy in immunogenic roles among microbiotas. Fecal transplantation trials in germ-free mice provided “the proof of principle” that germ-free mice reproduce the donor’s microbiome and corresponding ICI efficacy. However, species-specific biological differences prevent direct extrapolation between the results in murine and human models. Fecal transplantation or supplementation with microbes found in ICI responders requires caution due to potential adverse events.

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