Abstract: PURPOSE: To investigate the effect of photodynamic therapy(PDT) combined with scaling and root planing and only scaling and root planing in the management of distal alveolar bone resorption of mandibular second molars. METHODS: A total of 82 mandibular second molars in 57 patients whose mandibular third molars were mesially impacted and distal alveolar bone were resorbed were randomly divided into experimental group and control group. In the experimental group, the distal surface of the distal root of the mandibular second molar received scaling and root planing combined with PDT after mandibular third molar was extracted, while the control group only received scaling and root planing. The observation lasted for 1 year, the tooth mobility, probing depth (PD), clinical attachment level (CAL) and the osseous defect depth(ODD) were examined and recorded. The data were compared and analyzed using SPSS 25.0 software package. RESULTS: There was no significant difference in tooth mobility of mandibular second molar between the two groups at 1 week, 3 months, 6 months and 12 months after surgery (P>0.05). PD and CAL in the experimental group were significantly improved at 3 months, 6 months(P<0.05), while the clinical outcome changes at 1 week and 12 months after surgery between the 2 groups were not significant(P>0.05). There was no significant difference in ODD between the two groups 12 months after surgery(P>0.05). CONCLUSIONS: In the short term (< 6 months), PDT combined with scaling and root planing on the distal surface of the mandibular second molar distal root is more effective than scaling and root planing alone, when the mandibular third molar is mesially impacted and the distal alveolar bone of mandibular second molar is resorbed.

Key words: Scaling and root planing, Photodynamic therapy, Mandibular second molar, Alveolar resorption