Andreas Moritz
One of the best external methods to help with tooth cavities is the use of xylitol sugar. It helps to flush out bacteria lodging there. Xylitol toothpaste and xylitol mints, as well as xylitol gum (after meals) are the things to use. You can search for them on the web. For example Globalsweet.com has such products.
Of course, tooth decay comes from the inside, so keeping the gastro-intestinal tract neat and clean and eating natural, fresh produce prevents most tooth problems (see The Key to health and Rejuveantion, www.1stbooks).
With kind regards,
Andreas