Dental root-canal treatment. Coloured pan-oral X- ray of the mouth of a 17 year old woman showing a number of fillings (red) in teeth of the upper jaw, including root-canal treatment. In four of the upper incisors, the roots of the teeth have been drilled to remove the pulp which is diseased or has died. These teeth have then been filled and sealed. Other teeth reveal more superficial dental fillings. Dental caries (tooth decay) is the most common reason for this type of treatment. Good dental hygiene, such as regular brushing and consuming less sugar, can help to prevent tooth decay.