Alveolar bone resorption often occurs after tooth extraction. At present, guided bone regeneration technique is widely used in clinic since it leads to less trauma and less complications. Tenting screw technology, basic on the classical GBR, implants screws into the surgical area to prevent the barrier membrane from collapsing. Moreover, advanced platelet rich fibrin and injectable platelet-rich fibrin are used to provide the osteogenic function. The investigators intend to increase vertical alveolar bone augmentation by combining tenting screws and A-PRF, I-PRF.

Alveolar bone resorption often occurs after tooth extraction. At present, guided bone regeneration technique is widely used in clinic since it leads to less trauma and less complications. Tenting screw technology, basic on the classical GBR, implants screws into the surgical area to prevent the barrier membrane from collapsing. Moreover, advanced platelet rich fibrin and injectable platelet-rich fibrin are used to provide the osteogenic function. The investigators intend to increase vertical alveolar bone augmentation by combining tenting screws and A-PRF, I-PRF.

Inclusion Criteria:

1. 18-80 years old;
2. single tooth in the maxillary posterior area cannot be retained (third degree loosening / alveolar bone resorption to the periapical area), implantation is needed after extraction, and CBCT shows vertical bone defect ≥ 3mm;
3. 4 weeks after extraction or missing teeth within 3-5 weeks;
4. adjacent teeth exist and loosening is less than Ⅰ degree;
5. periodontal disease in inactive stage, whole mouth bleeding index (FMBS) is less than 20%;
6. thick gingival biological type.
7. CBCT shows that the bone of the edentulous site meets the requirements of tent screw implantation (bone height ≥ 3mm and bone mineral density is sufficient);
8. the patients and their families have informed consent and signed the informed consent form.

Exclusion Criteria:

1. pregnant and lactating women;
2. smoking (> 10 cigarettes per day) and alcoholism;
3. taking anticoagulants within 3 months before operation;
4. suffering from autoimmune diseases, diabetes, liver disease, blood system diseases and infectious diseases;
5. patients taking any drugs that affect platelet function or whose platelet count is less than 200000/mm3 3 months before blood collection;
6. patients who have been treated with bisphosphate / steroids for a long time;
7. have received alveolar ridge bone augmentation surgery;
8. previous history of radiotherapy in the head and neck;
9. acute inflammation in edentulous sites;
10. inability to maintain good oral hygiene or follow-up visits as required.