Abstract: BACKGROUND: Disorders of calcium metabolism mediate the occurrence and development of chronic fluorosis, but the specific molecular mechanism has not been elucidated and there is little systematic discussion on the role of calcium ion (Ca2+) in the pathogenesis of chronic fluorosis.
OBJECTIVE: To review the role of Ca2+ in chronic fluorosis, thereby providing new ideas and perspectives for the exploration of the molecular mechanism of chronic fluorosis and the development of targeted drugs.
METHODS: “Ca2+, fluorosis, pathogenesis, calcium overload, oxidative stress, endoplasmic reticulum stress, mitochondrial damage, apoptosis” were used as Chinese and English keywords, and the relevant literatures included in PubMed database and CNKI database from January 2000 to January 2022 were retrieved. After removal of obsolete, repetitive and low-credibility documents, 110 documents were finally included. 
RESULTS AND CONCLUSION: Ca2+ plays an important role in the pathogenesis of chronic fluorosis. The calcium paradox forms of low extracellular calcium caused by bone calcium metabolism disorder and of high intracellular calcium caused by intracellular Ca2+ metabolism disorder jointly induce the damage of fluoride to the bone and non-bone tissues. Intracellular Ca2+ metabolism disorder, with calcium overload as the core link, mediates the occurrence and development of chronic fluorosis. The specific process is as follows: fluorine promotes the production of chronic fluorosis through the inhibition of calcium transporters/enzymes in the plasma membrane and endoplasmic reticulum and the interference of gene expression levels. Cytoplasmic calcium is overloaded, thereby activating the downstream calcium signal transduction pathway, forming a unified negative regulatory network with multiple mechanisms, such as oxidative stress, endoplasmic reticulum stress, mitochondrial damage, and jointly inducing apoptosis in bone and soft tissue cells. In contrast, calcium agents and inhibitors that act on intracellular calcium-related targets (LTCC Cav1.2, NMDARs, and CaM-CAMKII) exert therapeutic effects by reversing fluoride-induced calcium paradoxes. Recovery from Ca2+ metabolism disorders is an important approach for treating chronic fluorosis. From another point of view, this not only provides an immediate theoretical basis for the current clinical application of calcium agents, but also provides new ideas and confidence for the development of drugs acting on calcium-related targets in the future.

Key words: calcium ion, fluorosis, pathogenesis, calcium overload, oxidative stress, endoplasmic reticulum stress, mitochondrial damage, apoptosis