Evaluation of outcomes
PD
SECONDARY, CREST
The investigator was not involved in the surgery and randomization, who was also not aware of the assignment of groups. Clinical data and imaging data were measured by two different investigators. The researchers analyzed the measurements of primary outcome variables including the height and width of bone repair in the extraction socket, and secondary outcome variables including PoSSe scale, PD and degree of gingival recession.Postoperative symptom severity (PoSSe) scale was a questionnaire developed by Ruta et al. [The PD of periodontal socket at distal buccal axis angle (PD-B), lingual axis angle (PD-L) and alveolar crest (PD-M) of the second molar were measured at 3rd, 6th and 12th months after surgery in all three groups. The distance (CG) between the cemento-enamel junction (CEJ) and the gum (G) of the second molar was measured to calculate the degree of gingival recession.Baseline values of each measurement index before extraction of the third molar were measured by CBCT: ① The distance between the distal root apex (point A) of the second molar and the lowest point (point B) where the third molar’s crown connects with the second molar, AB; ② The distance between point B and CEJ of the second molar (point C), BC; ③ The distance between the point C and the contact point (D) of the alveolar bone and the distal of the third molar, CD; ④ The lowest point (B) of the third molar connect with the distal root of the second molar is compared to the depth of the distal root of the second molar, AB/AC. In addition, the vertical height (BE) and horizontal distance (DF) of new bone at 3rd, 6th and 12th months after surgery, the value of ∠CEF, the relative vertical height (BE/BC) and relative horizontal distance (DF/CD) of new bone were measured (Fig. 
The CBCT measurement methods (