Revascularization is an alternative new treatment of immature permanent teeth with necrotic pulp nowadays while apexification is the traditional therapy. The investigators suppose that revascularization is superior to apexification at developing the root of immature permanent teeth and reducing the risk of root fracture,and the research is designed.

The investigators design to collect a group of patients presenting immature permanent teeth with periapical periodontitis in certain criterion. The investigators will divide the patients into two groups randomly. One group will get treated with revascularization while the other with apexification. The investigators want to evaluate the short-term and long-term effects of the two groups to get a conclusion of the clinical value of revascularization.

Inclusion Criteria:

• clinical diagnosis of periapical periodontitis
• must be immature permanent teeth
• must be local Guangzhou

Exclusion Criteria:

• blood disease
• residual root that is advised to extract
• serious periodontitis
• women in pregnancy