Objective To investigate the effect of low-level laser on periodontal bone remodeling factors during orthodontic retention after tooth movement in rats.Methods A total of 80 Wistar rats were randomly divided into blank control group and 4 model groups (relapse group,retention group,retention+laser group,and relapse+laser group),with 16 rats in each group.In the blank control group,no active force was applied and no measures were taken.The first molar mesial movement model was constructed in the other 4 groups,and the intraoral device was removed after 21 d of active force application.The relapse group was equipped without retention device,the retention group was equipped with retention device,the retention+laser group was equipped with retention device and irradiated with low-level laser every other day,and the relapse+laser group was equipped without retention device but irradiated with low-level laser every other day.The rats were sacrificed on the 2^nd,5^th,10^th and 15^th day of the retention period after 21 d of active force application,and the total RNA of 2-mm tissues around the first molar was extracted.The mRNA expression of bone remodeling factors (Runt-related transcription factor 2[Runx2],alkaline phosphatase[ALP],type Ⅰ collagen[COLⅠ],nuclear factor of activated T cell[NFATc],cathepsin K[CTSK],and matrix metalloproteinase 9[MMP9]) were detected by quantitative polymerase chain reaction (qPCR).Results The mRNA expression of the 6 bone remodeling factors in the 4 model groups was higher than that in the blank control group,and the differences were statistically significant at most time points (all P<0.05);the mRNA expression of the 6 bone remodeling factors in the relapse group was significantly higher than that in the retention group at each time point (all P<0.01).As time went on,the mRNA expression of 6 bone remodeling factors in the retention+laser group was higher than that in the retention group,and the difference was significant from the 5^th day (all P<0.05) and peaked on the 10^th day.Except for the MMP9,the mRNA expression of the other 5 bone remodeling factors in the relapse+laser group was higher than that in the relapse group at most time points (all P<0.05).Conclusion In the retention process of the first molar in rats,the low-level laser can increase the expression of bone remodeling factors and accelerate the remodeling of alveolar bone.