A tooth is made up of enamel (the outer layer), dentin (the second layer) and the pulp (the innermost layer of the tooth; commonly referred to as the nerve). The dental pulp is the part in the centre of a tooth made up of living connective tissue and cells called odontoblasts (the cells that form the tooth).
When a tooth experiences trauma or has decay which is left untreated, the nerve of the tooth can die. This can cause extreme pain, a possible abscess or necrosis of the bone (bacteria eating away or diminishing bone structure).
The infected pulp is removed, the space where it resided is thoroughly cleaned, shaped and disinfected and a rubber-based filling material is packed within. A filling can then restore the tooth back to its original shape and function.
After this procedure, the tooth becomes more fragile and a crown should be placed to prevent the tooth from fracturing.