Tooth root sensitivities: Oversensitivity of exposed roots of teeth to cold, hot, and sour foods because those roots are no longer protected by healthy gum and bone. Chronic gum disease contributes to toothache due to root sensitivities. The roots are the lower 2/3 of the teeth that are normally buried in bone. The bacterial toxins dissolve the bone around the roots and cause the gum and the bone to recede, exposing the roots. The sensitivities may be so severe that the person avoids any cold or sour foods.