To preliminatively investigate the changes of inflammatory factors and microbial flora distribution in the environment around implants following photodynamic therapy (PDT) combined with subgingival sandblasting therapy, and to provide theoretical basis for the application of PDT in the treatment of peri-implant inflammation.

A single-center prospective, open-label, randomized controlled study were adopted. Total of 9 patients and 16 implants were recruited from February 1st, 2018 to February 1st, 2019 in the Department of Stomatology of Beijing Chaoyang Hospital, Capital Medical University. Gingival crevicular fluid (GCF) was extracted from patients with peri-implantitis before combined therapy and after different treatment times, the changes of microflora in GCF were detected by amplifiers. Furthermore, changes of microflora distribution in GCF were revealed by bioinformatics analysis, in order to analyze the possible mechanism of PDT in the treatment of peri-implantitis from the point of view of pathogenic bacteria. In Alpha diversity analysis, R software was used for difference analysis, and rank-sum test was used for test.

All patients completed the planned follow-up. The α diversity analysis of GCF samples of patients before and after combined treatment showed that Observed species, Chao and Ace index of 5 groups of patients were all higher than before treatment, and Chao index showed significant difference among groups (χ² = 5.688, P = 0.033). β diversity analysis showed no significant difference in community diversity among groups (all P > 0.05). The principal coordinate analysis based on the unweighted Unifrac distance showed that the difference between the two groups was significant at 24 weeks after treatment. The pairwise comparison between the two groups confirmed that the β diversity was significantly different from that of the other five groups (P: χ² = 7.751, P = 0.005; W1: χ² = 6.471, P = 0.011; W2: χ² = 4.997, P = 0.025; W4: χ² = 3.612, P = 0.0415; W12: χ² = 3.125, P = 0.0486), indicating that colony diversity was significantly different from that of the former group at 24 weeks after treatment without considering abundance information.

There was no significant change in the composition of GCF in patients before and after combined therapy. The species diversity at 24 weeks after treatment was significantly higher than before, mainly reflected in the increase of non-dominant bacteria, which provides a theoretical basis for further study of the role of this therapy in the regulation of local microecological environment and long-term maintenance of peri-implantitis.