Disease in the mouth is caused by a shift in the oral environment allowing normally present 'bad' bacteria to overgrow.

“what causes disease or disease is the specific bacteria but it's not true we all have all those bacteria in your mouth uh it's indigenous to you is not that it's from something external you have that it's a their normal habit that is your mouth but for some reason you don't stop brushing or you start taking medication and your mouth becomes dry you have a health condition that allows inflammation to to be more prevalent you know my all those things might change the cavity environment and that allows some bad bacteria to grow and supersede the good ones”