I’ve healed several cavities in my teeth with a good diet and some anti-bacterial tricks. Someone wrote to ask me if a cavity which has progressed into the dentin can also be healed. The answer is yes, lesions (holes) 200 microns into dentin remineralized according to a 2001 study published in the Journal of Dental Research. ( The study used obscene amounts of flouride, but I don’t think you need it. I healed my own cavities without it. )
Remineralization of caries lesions extending into dentin
Keep in mind, however, that the bacteria can get into your blood stream so you really should have a cavity filled if it gets bad. Find a laser dentist to fill it so the tooth is sterilized in the process. Then stop eating so much sugar!