Tooth decay can only worsen with time. If you do not seek dental treatment, the decay can progress into a toothache, and may eventually require further treatment or result in the loss of that tooth.
When the decay reaches the nerve of your tooth, you may begin to experience extreme tooth sensitivity and pain. Eventually a dental abscess may form and the tooth might fracture and may have to be extracted.
On the other hand, if treatment is sought early, a dental filling could be placed to restore the decaying tooth. Your dentist will be able to recommend the suggested treatment for your decayed tooth.