I used to have bad teeth also. What helped me was avoiding grains like wheat, limiting sugar, and keeping my testing vitamin D3 levels around 50ng/ml. I also take vitamin K2, which seems to help.
Pretty much what I did to improve my teeth is what Dr. Mellanby discovered. Drs Mellanby where the husband and wife English researchers that discovered vitamin D3, plus conducted studies on dietary ways, along with taking vitamin D3, to prevent dental disease.
"Dr. Mellanby's Tooth Decay Reversal Diet" wholehealthsource.blogspot.com/2010/12/dr-