There weren't really "dentists" per-se in the Medieval era. Rather, when there were teeth issues one went to the nearest barber or perhaps a local physician. The most common Medieval solution for a toothache would have been ignore it if it were only mild, or have the tooth pulled if it were more severe. Given how much lower in sugar the medieval diet was however, this would have been a fair bit less common than it might seem. Day to day dental care would have mostly consisted of rinsing and possibly scrubbing with some sort of herb or maybe a fibrous material, though it varies greatly over time and place.

Further reading / source: http://gallowglass.org/jadwiga/herbs/teeth.html