| Objective: Periodontitis is an inflammatory,destructive disease involving periodontal supporting tissues caused by dental plaque and is the main cause of tooth loss in adults.After tooth loss,the alveolar ridge undergoes varying degrees of resorption due to physiological modeling and remodeling,resulting in poor soft and hard tissue morphology in the missing tooth area,making implant treatment more difficult.Alveolar ridge preservation(ARP)is a procedure to preserve or reconstruct the hard and soft tissues by placing biomaterials in the extraction sockets after tooth extraction to slow down or interrupt the resorption of the alveolar ridge.ARP is safe and effective in stage Ⅲ/Ⅳ periodontitis where the tooth cannot be retained,and it can reconstruct the hard and soft tissues,simplifying the procedure of subsequent implant treatment.However,the treatment of soft tissue wound in alveolar ridge preservation remains somewhat controversial.The purpose of this study was to evaluate the effect of alveolar ridge preservation by using three soft tissue treatment modalities: full-thickness flap reduction sutures,minimally invasive sutures and delayed surgery after extraction of teeth with stage Ⅲ/Ⅳ periodontitis that could not be retained,and to provide guidance for the clinical application of soft tissue treatment modalities for this procedure.Methods: This study was a prospective non-randomized case-control study.According to the inclusion and exclusion criteria,20 patients(male: 11;female: 9)with stage Ⅲ/Ⅳ periodontitis,with a total of 24 non-retentive affected teeth(maxillary: 6;mandibular:18),were included and divided into 3 groups: the subtraction suture group,5 patients(male: 3;female: 2),with a total of 6 affected teeth(maxillary: 0;mandibular: 6),using a full-thickness flap with vertical subtraction incision;in the minimally invasive group,8patients(male: 4;female: 4)with 10 affected teeth(maxillary: 2;mandibular: 8)were treated with a minimally flap or flapless,collagen sponge covering the barrier membrane;in the delayed surgery group,7 patients(male: 4;female: 3)with 8 affected teeth(maxillary: 4;mandibular: 4)were treated with extractions.The affected teeth were naturally healed for 4 weeks before alveolar ridge preservation,and the gingival flap was repositioned and sutured in situ to close the wound.The relevant clinical indicators were measured and recorded,and the preoperative and 6-month postoperative CBCT was superimposed to measure the imaging indicators using In Vivo Dental Anatomage 6.0.5software:(1)Clinical periodontal indicators: the probing depth,clinical attachment loss,bleeding index,tooth mobility and gingival recession of the affected teeth were measured before extraction.(2)Soft tissue index: The buccal keratinized mucosal width and changes and buccal mucosal thickness and changes were measured clinically before surgery and 6 months after ARP,the supracrestal tissue height was measured 6 months after ARP,and the soft tissue early healing index was applied to assess the wound healing status at 2,4 and 8 weeks after ARP.(3)Hard tissue indexes: The vertical height and changes of the buccal and lingual bone walls,horizontal width and changes of the alveolar ridge,alveolar bone augmentation,alveolar ridge morphology,alveolar bone density,the relationship between bone wall thickness and alveolar ridge resorption,and alveolar bone height of adjacent teeth were measured and recorded before surgery and 6months after ARP using CBCT images.(4)Pain assessment index: The visual analog scale was applied to record the pain level of patients immediately after surgery,2 weeks after surgery and 4 weeks after surgery.Statistical analysis was performed using SPSS26.0.Results:(1)Clinical periodontal indices: there were no significant differences in probing depth,clinical attachment loss,bleeding index,tooth mobility and gingival recession of the affected teeth in each group before extraction.(2)Buccal keratinized mucosal width: 6 months after ARP,the buccal keratinized mucosal width was significantly reduced(P<0.05)from preoperative levels in the reduced-tension suture group at the proximal,central and distal sites,with changes of-1.8 ± 1.0 mm,-2.1 ± 1.5 mm and-2.1 ± 1.0 mm,respectively;the keratinized mucosal width was significantly reduced(P<0.05)from preoperative levels in the minimally invasive group at the central and distal sites.There was no significant change in the width of the corneal mucosa at each site in the delayed surgery group compared with that before surgery(P>0.05),and there was a significant difference in the amount of change in the width of the corneal mucosa between the groups,and the width of the corneal mucosa in the reduced-tension suture group was more reduced than that in the minimally invasive group and the delayed surgery group(P<0.05).(3)Buccal mucosal thickness: After 6 months of ARP,there was no significant difference in the amount of change in buccal mucosal thickness between the reduced-tension tight suture group,the minimally invasive group and the delayed surgery group.(4)Supracrestal tissue height: After 6 months of ARP,the supracrestal tissue heights were 2.1±0.4 mm,2.3±0.7 mm and 3.8±0.4 mm in the subtended tight suture group,minimally invasive group and delayed healing group,respectively,with significant differences between the delayed healing group and the subtended suture group,and between the delayed healing group and the minimally invasive open suture group(P<0.05),and there was no significant difference between the subtended tight suture group and no significant difference between the minimally invasive open suture group and the reduced tension suture group.(5)Early soft tissue wound healing index: the soft tissue wound healing scores gradually decreased at 2,4 and 8 weeks after surgery,and at 2,4 and 8 weeks after surgery,the healing index decreased more significantly(P<0.05)in the deferred surgery group than in the reduced-tension tight suture group and the minimally invasive open suture group,and there was no significant difference between the reduced-tension suture group and the minimally invasive group.(6)Vertical height of alveolar ridge: After 6 months of ARP,there was no significant reduction in the vertical height of buccal alveolar ridge,but there was a significant reduction in the vertical height of lingual alveolar ridge at some sites(P<0.05),including the proximal-central,central and distal-central sites in the reduced-tension tight suture group,with changes of-1.5 ± 0.9 mm,-1.4 ± 0.8 mm and-1.5 ± 0.8 mm,respectively;in the minimally invasive open suture group The central and distomedial sites were significantly lower(P<0.05),with changes of-0.9 ± 0.9 mm and-0.8 ± 0.8 mm,respectively,and the central site was significantly lower(P<0.05)in the deferred surgery group,with a change of-1.2 ± 0.69 mm.There was no significant difference in the amount of change in the vertical height of the buccal and lingual alveolar crest between the groups.(7)Alveolar ridge horizontal width: 6 months after ARP,the alveolar ridge horizontal width increased significantly(P<0.05)at 1 mm in the crestal root direction,and there was no significant difference in the amount of change in alveolar ridge horizontal width between the three groups;at 3 mm in the crestal root direction,there was no significant difference in the amount of change in alveolar ridge horizontal width between the three groups;at 5 mm in the crestal root direction,there was a statistically significant difference in the central site in the reduced-tension tight suture group compared with the preoperative site.The amount of change was-0.5±0.3 mm,and the amount of change in the horizontal width of the alveolar ridge was not significantly different between the three groups.(8)Alveolar bone augmentation: The height of alveolar bone augmentation in each group exceeded the depth of the alveolar sockets before surgery,and there was no significant difference in the percentage of bone augmentation between the three groups.(9)Alveolar bone density: 6 months after ARP,the alveolar bone density in the edentulous area of patients ranged from 540.0 to 593.8 HU,and there was no statistical difference in alveolar bone density between the three groups.(10)Alveolar bone morphology: 6 months after ARP,the alveolar bone morphology of the reduced-tension tight suture group,the minimally invasive open suture group and the postponed surgery group were all RM type II or RM type III,and there was no significant difference in the alveolar bone morphology type among the three groups.(11)The relationship between bone wall thickness and alveolar ridge resorption: 6months after ARP,the thicker the alveolar crest bone wall,the less resorption of the alveolar bone.For sites with alveolar crest bone wall thickness less than 0.5 mm,all of them were resorbed;for sites with alveolar crest bone wall thickness more than 2 mm,only 7% of them were resorbed.(12)Alveolar bone height of adjacent teeth: After 6 months of ARP,there was no significant change in alveolar bone height of adjacent teeth in each group,and there was no significant difference in the amount of change in alveolar bone height of adjacent teeth between the three groups.(13)Postoperative pain index: The postoperative pain index decreased gradually in the reduced-tension tight suture group,minimally invasive group and delayed surgery group immediately,2 weeks and 4 weeks after surgery,and there was no significant difference in the postoperative pain index among the three groups.Conclusions: The affected tooth of stage Ⅲ/Ⅳ periodontitis,the alveolar ridge preservation by means of reduced tension suture,minimally invasive suture and delayed surgery after extraction can better preserve or reconstruct the alveolar bone in the edentulous area,and the delayed alveolar ridge preservation has certain advantages for the wound healing and soft tissue preservation. 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