My youngest son is on a very strict paleo diet.

He is not a good tooth brusher. Actually a very poor brusher.

My two older kids are on SAD.

They are good brushers/ flossers.

guess who never has cavities and has perfect gums?

Although this is a small statistical sample, the subject on paleo diet with
inadequate brushing and nonexistent flossing has had zero cavities and
perfect gums.

The two subjects on SAD have had cavities/ gum/ dental problems despite a
strict and thorough brushing/ flossing regimen.