Inclusion Criteria:  18-80 years old; 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; 4 weeks after extraction or missing teeth within 3-5 weeks; adjacent teeth exist and loosening is less than Ⅰ degree; periodontal disease in inactive stage, whole mouth bleeding index (FMBS) is less than 20%; thick gingival biological type. 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); the patients and their families have informed consent and signed the informed consent form.  Exclusion Criteria:  pregnant and lactating women; smoking (> 10 cigarettes per day) and alcoholism; taking anticoagulants within 3 months before operation; suffering from autoimmune diseases, diabetes, liver disease, blood system diseases and infectious diseases; patients taking any drugs that affect platelet function or whose platelet count is less than 200000/mm3 3 months before blood collection; patients who have been treated with bisphosphate / steroids for a long time; have received alveolar ridge bone augmentation surgery; previous history of radiotherapy in the head and neck; acute inflammation in edentulous sites; inability to maintain good oral hygiene or follow-up visits as required.