In ancient Egyptian times, you were more likely to suffer from a toothache if you were well-to-do. This was because those who could afford to ate sweets (such as honey), while the working class ate more onions.
Onions are known to be high in sulfur, an important mineral for both teeth and bones.  They also possess anti-inflammatory benefits and may even improve blood-sugar blance.  Blood sugar imbalances, on the other hand, can also accelerate tooth decay and bone loss.