It is not the teeth that smell rotten, the odour is caused by all the dead bacteria on your tongue.

Normally our mouth is filled with good lactobacilles from the day we first got our mothers milk. The tiny babies have never bad breath.
Yet as soon they get their first teeth, the loving mothers fill their mouth with tooth paste, and the odour soon developes. Happily most pastes for babies are less harming, and the babies do not have too much problems with the odour.

Later when children become young adults, they try to eradicate all bacteria from their mouth, and they use tooth pastes with detergents like Sodium Lauryl Sulphate, or Sodium Laureth Sulfate. They kill all the good lactobacteria and soon their mouth is filled with bacteria of decay. They get a problem that they never had as babies, their breath begins to stink rotten. Now they buy more and more detergents, and get more and more desperat.

The smell gets so strong, that they cannot come near anybody, they feel outside.

Others that use just a little tooth paste, haven't the same problems, and they admonish the unhappy person to brush his teeth better. He cannot but try more and more, but nothing helps!

Soon the gingiva gets inflamed, and the teeth bleed when brushed.

After loosing all the teeth the problem disappeares because there is no need to put toothpaste in the mouth. False teeth are washed outside the mouth, and the good lactobacteria can grow in the mouth, and it doesn't smell.

I have worked many years in old peoples homes, and allways noticed the same thing: persons without teeth do not smell. Persons with only false teeth do not smell.   Persons that have different detergents and pastes for their teeth smell rotten, when you are near.