Hi. There must be a cavity in the said tooth that must have gone really deep into the pulp... This being the reason for your severe continuous pain. Once the pulp inside the tooth gets exposed.... A normal filling won't be the solution. Hence a root canal treatment is adviced.. Wherein the infected pulp will be cleaned out and the canals in the root will be cleaned.. Shaped and filled with a dental material called gutta percha. Once this is done.. The tooth will be restored with a filling on top followed by a cap which will reinforce the strength of the tooth n prevent a fracture. This is in short what an R. C. T is all about