Dental stem cell proliferation and osteoblast differentiation are key cellular processes involved in periodontitis diseases. Researchers have found that SIRT1 (sirtuin 1, silent mating type information regulation 2 homolog 1) and microRNAs play a pivotal role in the process, but a clear underlying mechanism has not been determined. In this study, the has-miR-22-3p that target SIRT1 was predicted by TargetScan. Luciferase reporter assay was used to confirm that SIRT1 is the direct target of miR-22-3p. Importantly, miR-22-3p was revealed to control SIRT1 in periodontal ligament stem cell (PDLSC) and to regulate the proliferation and differentiation of PDLSC by SIRT1 silencing. Furthermore, we detected the induction of miR-22-3p expression by nicotinamide treatment on PDLSC. Induction of PDLSC proliferation and differentiation by nicotinamide treatment was blocked by miR-22-3p knockdown. These results suggested that the effect of nicotinamide on PDLSC is through miR-22-3p. In addition, miR-22-3p also upregulated the expression levels of the inflammatory cytokines tumor necrosis factor-α, interleukin-1β (IL-1β), and IL-8 in PDLSC through SIRT1 pathway and downregulated the expression of TLR-2 and TLR-4. miR-22-3p is a new target either for the treatment of periodontitis or the improvement of inflammation caused by orthodontics.