You definitely want to avoid tooth problems if you no longer have access to modern dental care. One way to avoid problems in an uncertain future is to take good care of your teeth now. Regular dental check-ups and cleanings, and daily brushings are a must.
You can stock-pile toothpaste in your emergency supplies if you want to, but it's not really necessary. Back in the day, the purpose of tooth powder was to clean your teeth, not to give you a brighter, whiter, sexier, better smelling smile like today. Most people back then used a mixture of salt and baking soda to brush their teeth. Tooth powder was kept in a can. You could shake a little out into the palm of your hand, wet the bristles of your tooth brush, dip the bristles down into the powder, and brush away. Pictured below: Home made tooth powder and twig brush.
If a toothbrush was not available, the old-timers would cut a small stick (usually from a gum tree or a willow) and chew the end until it kind of splintered up into a brush. This improvised brush was then used to brush the teeth. Pictured below: Brush made from gum tree twig
I do keep a few dental items in my emergency supplies. I have a little dental repair kit that consists of a topical numbing agent, a small wooden spatula, some dental putty to temporarily fill cavities, and some dental adhesive that can be used to temporarily glue on broken crowns or dropped fillings. Pictured below: Emergency dental repair kit
I also keep a bottle of oil of clove. Clove oil has been used to treat toothaches for centuries.
A topical oral anesthetic like Anbesol or Oragel can also be very handy. Pictured below: Oral topical anesthetic
I have a supply of broad spectrum antibiotics that can be used to help with abscesses and infections. And I always have a bottle of bourbon and a pair of vice grip pliers. I guess you could call these my last resort dental care items. Sure hope I never have to use them.
There is a book available called Where There is No Dentist. This book is intended for use by aid workers in third world countries, and it is written on a pretty understandable level with the layman in mind. It is available for purchase from the Hesperian foundation or you can download the fairly massive pdf file for free. Just do a search for "Where There is No Dentist" and you'll see a couple of different places where you can download the book.