1. The claim that this strain outcompetes the same S mutans from occupying the same niche cannot be true unless this strain is also capable of creating and tolerating environments with low pH. By definition if it creates acid to the same degree it will also cause cavities.
2. Single applications are insufficient to cause any persistent colonization. Even multiple daily applications of oral probiotics don’t lead to colonization. Oral probiotics function primarily through bacteriocins, not through colonization (except in very rare cases). This is because the existing microbiome is incredibly difficult to outcompete. The community in your mouth has evolved for as long as you have lived, and in some ways was shaped for generations before as it’s technically inherited from your ancestors.
3. S mutans is not the only species that causes cavities. S sobrinus, S wiggsiae, B dentium, about a dozen other acidogenic species also cause cavities.
Source: I’m a cofounder at Bristle Health, the oral microbiome company.
> cannot be true unless this strain is also capable of creating and tolerating environments with low pH
Whether it can tolerate low pH environments is not particularly related to whether it creates low pH environments. If it's agnostic to pH levels around that range, then it can inhabit that niche whether or not there is acid being secreted.
S mutans creates incipient lesions by making acid, incipient lesions are micro environments where the low pH that causes enamel decay is determined by the biofilm on its surface. S mutans cannot thrive in environments with neutral or high pH. the existing community (including other Streptococcus species) create local alkaline environment via multiple metabolic pathways, including the most well studied and prevalent arginine deiminase system. A “normal” healthy community antagonizes S mutans by maintaining a normal pH in saliva and the tooth surface, preventing stable colonization by S mutans.
Without acid production, S mutans cannot stably colonize. and is readily outcompeted by the existing community. Any novel strains of S mutans to “compete for the same niche” will suffer the same weakness unless they create acid. but if this “probiotic” also creates acid, then by definition it also causes cavities.
edit: adding citation https://www.futuremedicine.com/doi/10.2217/fmb-2018-0043