Jeffrey Hillman from the University of Florida developed a genetically modified strain of Streptococcus mutans called BCS3-L1, that is incapable of producing lactic acid – the acid that dissolves tooth enamel – and aggressively replaces native flora. In laboratory tests, rats who were given BCS3-L1 were conferred with a lifetime of protection against S. mutans. BCS3-L1 colonizes the mouth and produces a small amount of a lantibiotic, called MU1140, which allows it to out-compete S. mutans. Hillman suggested that treatment with BCS3-L1 in humans could also provide a lifetime of protection, or, at worst, require occasional re-applications. He stated that the treatment would be available in dentists' offices and "will probably cost less than $100." The product was being developed by Oragenics, but was shelved in 2014, citing regulatory concerns and patent issues. In 2016, Oragenics received a 17-year patent for the product.
You left out the next paragraph which is may be one of the reasons it's not used:
> On rare occasions the native S. mutans strain escapes into the blood, potentially causing dangerous heart infections. It is unclear how likely BCS3-L1 is to do the same.
That would be a really weird reason. The natural bacteria has the exact same problem. The engineered one is uncertain to have the problem. Why would you opt for the one that definitely carries the risk and ALSO causes expensive tooth decay?
Because the engineered caries might behave differently and unexpectedly. Regular caries has a pretty hard time getting into the bloodstream and won't infect other regions. Can the immune recognize the new strain? Can the new strain infect other regions of the body? Does it permeate into the bloodstream more often? There are more questions to be answered, experimentally.
a) Since there is a patent (Replacement therapy for dental caries [1]) it means many/some people should be able to make the product on their own.
b) How many more stories (and what kind of stories) of nefarious obstacles erected by the FDA are required until there is a large-scale sentiment to either abolish that agency or severely limit its (unconstitutional) powers? [2]
Jeffrey Hillman from the University of Florida developed a genetically modified strain of Streptococcus mutans called BCS3-L1, that is incapable of producing lactic acid – the acid that dissolves tooth enamel – and aggressively replaces native flora. In laboratory tests, rats who were given BCS3-L1 were conferred with a lifetime of protection against S. mutans. BCS3-L1 colonizes the mouth and produces a small amount of a lantibiotic, called MU1140, which allows it to out-compete S. mutans. Hillman suggested that treatment with BCS3-L1 in humans could also provide a lifetime of protection, or, at worst, require occasional re-applications. He stated that the treatment would be available in dentists' offices and "will probably cost less than $100." The product was being developed by Oragenics, but was shelved in 2014, citing regulatory concerns and patent issues. In 2016, Oragenics received a 17-year patent for the product.
[0]: https://en.wikipedia.org/wiki/Caries_vaccine#Attempts_using_...
[1]: https://www.newscientist.com/article/dn1941-gm-bacteria-may-...
[2]: https://www.ncbi.nlm.nih.gov/m/pubmed/12369203/