MMP9 and dental fluorosis: Taking the level of urine fluoride as the internal loading index and the extent of dental fluorosis the clinical effect index, it was found that with the increase in the urinary fluoride level and the extent of dental fluorosis, the serum BALP, MMP-2 and MMP-9 of the children gradually increased, and the OC and PTH gradually decreased, suggesting that BALP, MMP-2, MMP-9, OC, and PTH were closely related to the occurrence and development of dental fluorosis.