To evaluate the clinical effect of site preservation after third molars extraction by using tooth extraction of third molars with site preservation using bio-oss and bio-guide in preventing the formation of deep periodontal pockets in the distal of second molars.

The mandibular third molar is the last tooth to erupt in the dentition, and due to the insufficient eruption position, it can lead to different degrees of impact. During the eruption of impacted tooth, the crown may be partially or completely covered by the gingival flap. A deep blind pocket is formed between the gingival flap and the tooth crown, and food and bacteria are easily impinged in the blind pocket. Under the influence of oral environment and dental plaque, the presence of blind pockets can lead to the loss of periodontal attachment and the absorption of alveolar bone, thus affecting the distal periodontal status of adjacent molars.

Organic bone xenograft material composed of absorbable organic bovine hydroxyapatite is one of the commonly used transplantation materials for repairing bone defects. The application effect of allogeneic bone materials in periodontal therapy has been recognized by many experts and scholars. Guided bone regeneration (GBR), as a conventional periodontal bone graft, has achieved good results in periodontal tissue regeneration. Aljuboori et al. found that when the third molar was removed and GBR was performed at the same time, the depth of distal periodontal pocket probing of the adjacent second molar was significantly reduced in the re-examination 6 months after surgery.

Hence, this study intends to use xenograft combined with barrier membrane to improve the formation of distal periodontal pocket of the second molars after third molars extraction.

Inclusion Criteria:

• 26-45 years old
• Completely or partially impacted mandibular third molar
• No evidence of acute inflammation
• In good physical status and oral health
• Regular attendance at control visits

Exclusion Criteria:

• pregnancy or lactation
• Aggregate systemic pathologies such as diabetes, thyroid disorders, bone metabolism diseases, among others
• Patients taking calcium, bisphosphonates, glucocorticoids, or other drugs that can interfere with bone metabolism
• Patients with uncontrolled periodontal conditions, endodontic conditions and other oral disorders
• Heavy smoke (10 cigarettes/day or more)
• The second molar has no contact with the third molar, or the third molar crown has alveolar bone