**3. Endodontic regeneration in an infected root canal**

Given the proper environment, many body tissues are programmed to regenerate new cells in order to compensate for lost ones; dental pulp tissue is no an exception. One of the most critical factors for regeneration is a bacteria-free root canal to allow stem cells to continue to regenerate and grow the root further into its full maturation without any damage.

Sterilizing an infected root canal can be sometimes quite challenging since roughly 20 different bacterial species can be found in an infected root canal with chronic apical periodontitis [23]. In addition, the root canal anatomy can provide a good sanctuary for the microbiota to thrive, containing places antimicrobial agents have difficulty reaching, for example accessory canals, isthmuses and fins.

Teeth can be subjected to many conditions in which lead to bacterial contamination of the root canal. The most prevalent are caries lesions, traumatic injuries and dental anomalies. Caries lesions can cause pulp exposure in teeth with immature apex, often in the permanent first molars. Permanent first molars erupt at an early age (6 to 7 years old), often when children are not sufficiently skilled in maintaining adequate oral hygiene on their own. This explains why caries is more prevalent in children who live in families of low socioeconomic status that have the inadequate oral hygiene and/or poor dietary habits that lead to early dental caries [24].
