Root resorption can be divided into two main categories: internal root resorption and external root resorption. Internal root resorption is a pathology that can lead to tooth destruction in the short term and must consequently be stopped as soon as possible by applying adequate canal treatment. Until now, despite many research studies, very little is known about its causes and the way this kind of resorption appears. There are many different forms of external root resorption and it has a very diverse etiology. An external root resorption can thus appear in case of orthodontic treatment or due to the pressure brought by cysts, tumours or impacted teeth. A trauma or an infection may also lead to the development of an external root resorption. Because they are so diverse, each of these forms of external root resorption requires a specific treatment. It should also be noted that internal root resorptions, and some forms of external resorption too, often respond favourably to a calcium hydroxide treatment.