Discussion
PD, bone defect, pain, tooth
DENTIN SENSITIVITY, ADHESION
At present, alveolar surgery usually experiences a process of “destruction before reconstruction”. Awareness of the clinical protection for the second molar was absent after third molar extraction. The operation process is often too casual, only focusing on how to remove the tooth. Such surgical procedures might result in excessive alveolar bone defects, leading to the risk of bone absorption in the distal area of the second molar, dentin sensitivity and even tooth extraction. In order to explore new strategies for the clinical protection of the second molar after third molar extraction, this study provided two different methods for the repair of the distal bone defect of the second molar. Both could provide effective clinical protection by reducing the formation of periodontal pocket, alleviating gingival recession, and prompting bone defect repair. Especially in terms of short-term pain reduction, early bone defect repair and long-term reduction of PD, test B group containing CGF exhibited more obvious advantages.In terms of PoSSe scale, after tooth extraction there was almost no significant difference among all three groups except for pain perception. Test B containing CGF could significantly alleviate pain at the early stage, which was consistent with previous reports. Fang et al. [Concerning the depth of periodontal pocket and the degree of gingival recession, the PD-B and PD-M in test groups were significantly lower than that of the control group during short and long-term follow-up. Over 6 months, CGF and CGF membranes had better effects upon the healing of periodontal tissue and the reduction of gingival recession. CGF fibrin membrane is a blood agglutinate obtained by centrifuging venous blood specimens in a special centrifuge, which could produce fibrin with higher density and richer growth factors, therefore widely used in many clinical treatments and tissue engineering [Regarding defect repair, the vertical height and horizontal width of new bone of the two test groups were significantly better than that of the control group, and the angle of the distal infrabony pocket of the second molar was also significantly less than that of the control group. Bio-Oss has a porous structure as a bone substitute, which can guide the adhesion of osteoblasts, osteoclasts and so on, and change the structure of the filling material. It has been found that Bio-Oss can be retained for a long time in clinical application and participate in the process of new bone formation effectively [The vertical height of new bone in test A and test B groups was significantly different at 3rd and 6th month, and the bone repair ability of test B group was significantly better than test A group, indicating that CGF gel and CGF membrane could significantly promote bone defect repair ability in the early stage, which was consistent with most previous reports [In addition, our study also found that in the control group, if the horizontal impacted crown of the third molar was exposed on the gum and contacted with the distal root of the second molar, the periodontal membrane might be completely lost, the vertical bone height in the extraction socket was difficult to recover, and the infrabony pocket was basically formed based on the lowest point of the crown of the third molar. If the crown of the third molar was not exposed, the vertical height and horizontal distance within the extraction socket could be well repaired. The unrepairable alveolar bone might be attributed to the loss of periodontal membrane in the distal root surface of the second molar, which was a result of the inflammatory factors induced by long-term exposure of the crown. The lower position of extracted third molar crown, the more obvious repair of the vertical bone; the larger meso-distal width of the exposed alveolar bone of third molar, the lesser repair of vertical bone. Due to the limited sample size, the bias of present measurement results might be amplified. If this result is to be confirmed, a larger sample size would be required for further investigation.