Tooth pain. When i chew a hard food?

If you have developed black or brown spots of decay on your teeth either in the fissures or on the smooth surfaces and it is associated with discomfort and / or sensitivity to hot and cold and / or frank pain, it is likely that you have tooth decay. Your dentist will evaluate you comprehensively and based on his clinical and radiographic findings he will do one of the following; 1.Make an opening in the crown and remove decay, shape the cavity and fill it with a tooth colored filling or an amalgam filling. This could also be done under local anaesthesia. 2.If the decay is very deep and the pulp (nerve, root canal) is involved in the decay process he will, under local anaesthesia go deeper into the pulp chamber, remove the pulp and the nerve, render it free of infection, do a root filling and later put an amalgam or a tooth colored filling. Subsequently he will put a veneer or a crown on the tooth as the case may be.

May be you have caries in your tooth. Go for treatment as suggested by your dentist (filling or rct)