why is tooth decay still a thing? why haven't we modified s. mutans to degrade biofilms, or neutralize lactic acid? we can do it, why is it not widespread?

>a single application of the [modified] strain to human subjects should result in its permanent implantation and displacement over time of indigenous, disease-causing S. mutans strains.

see:
sci-hub.tw
/10.1007/978-94-017-2029-8_25