Objective:To evaluate the effects of photodynamic therapy (PDT) in extraction sockets of periodontally compromised molars on soft tissue healing, postoperative pain, bone density and bone height changes.Methods:This study is a single-center, single-blind, randomized controlled superiority clinical trial. Thirty-eight periodontally compromised molars requiring extraction in patients attending the Department of Periodontology, Stomatology Hospital, School of Stomatology, Zhejiang University School of Medicine, from December 2022 to September 2023 were included, and randomly assigned to PDT group and control group. The control group received routine debridement after extraction, while PDT group received routine debridement followed by PDT. The bucco-lingual and mesio-distal wound distances at 7 and 14 d after extraction were measured, and then the wound closure rates were calculated. Evaluating the soft tissue healing indexes at 7 and 14 d after extraction. The visual analogue scale was used to assess the pain level at 6 h, 1 d, 2 d, and 3 d after tooth extraction. Apical radiographs were taken immediately and 2 months after extraction in order to compare the changes of the bone density and height.Results:The wound closure rate at 1 week was (78.08±5.45)% in PDT group and (71.03±6.82)% in control group, with significant differences ( P<0.01). The wound closure rate at 2 weeks in PDT group [(85.88±3.84) %] was significantly higher than that in the control group [(81.66±3.79) %] ( P<0.01), but did not reach the superiority value of the superiority test (superiority value=10%, 95% CI at 1 week: 3.00%-11.12%, 95% CI at 2 weeks: 1.71%-6.73%). The soft tissue healing index of PDT group at 1 week was significantly better than the control group ( P<0.05), but there was no significant difference between the two groups at 2 weeks ( P>0.05). There was no significant difference between the two groups in terms of postoperative pain at 6 h, 1 d, 2 d and 3 d as well as in bone density and height changes at 2 months after tooth extraction ( P>0.05). Conclusions:PDT could promote soft tissues healing to some extent, but did not provide additional assistance in the healing of extraction sockets of periodontally compromised teeth. PDT did not show benefits on postoperative pain, changes of the bone density and bone height after tooth extraction.