There are five types of resorption that effect teeth:
External, internal, replacement resorption (ankylosis), peripheral inflammatory root resorption (PIRR) and internal-external progressive.

This is an example of the internal-external progressive type. The lesion begins laterally and extends internally, often surrounding the pulp. When opening the access there is copious bleeding and granulation-like tissue is removed. The bleeding is managed with calcium hydroxide dressings. Once the dry chamber is achieved, the lesion needs to be sealed at the external defect.

The xray to the right shows the fill in teeth exhibiting external resorption. These teeth can be difficult to obturate as the foramen is often opened following the resorptive process. Tooth number 12 is obturated with gutta percha and tooth number 11 is obturated with MTA.