A natural tooth consists of 3 layers: the outer enamel layer, the dentin layer, and the nerve of the tooth.
Tooth decay begins to occur in the enamel layer and is never painful. If tooth decay neglects, it reaches the dentin layer, where the patient begins to feel some varying degrees of pain, and then the decay reaches the nerve of the tooth. In this case, the pain is severe and the patient cannot bear it, and in many cases, the pain prevents the patient from sleep.
In the event that tooth decay reaches the nerve of the tooth, there are no solutions for the patient except to extract the tooth or make a nerve filling for the affected tooth.