Both methods tested in this study disinfect the non-vital root canals and induce blood clot formation inside the root canal. One method places calcium hydroxide inside the root canal after disinfection and the blood clot is induced four weeks later.

The other method performs disinfection and induction of blood clot in one appointment. The investigators hypothesize that both methods will obtain the same success rate in eliminating infection, increase in root length and canal walls thickness.

Collagen is placed on top of the blood clot, followed by white MTA. Glass ionomer is used to seal the access to the canal, which will be replaced by a permanent restoration 3 months later.

Inclusion Criteria:

• Healthy or having a mild systemic disease (ASA Physical Status 1 or 2), with no contraindications to the treatment.
• Cooperative.
• Clinical diagnosis of pulp necrosis based on cold test, electric pulp test as well as an identified cause of pulp necrosis such as caries, deep restorations, dental anomalies, history of trauma, associated with radiographic and/or clinic signs of periapical lesion.
• Open apex with a diameter of at least 1mm. For teeth with more than one apical foramen, at least one foramen needs to be 1mm wide.
• Tooth is restorable and periodontally stable.

Exclusion Criteria:

• Pregnancy.
• Evidence of pathological external or internal root resorption, root fracture or ankylosis.