Caries is the result of a disruption in the dynamic balance between demineralization and remineralization of the hard tissues of the teeth. Demineralization is the dissolution and loss of minerals in the teeth; and remineralization is the redeposition of dissolved mineral salts on the teeth. Fluoride can make the remineralization effect greater than the demineralization effect and stop the development of caries. When brushing teeth, the fluorine in the fluoride toothpaste is released and forms the fluoride-containing mineralization system with the mineral salts such as calcium and phosphorus in the paste. On the one hand, fluoride ions can replace the hydroxyl groups in the mineral salts of tooth tissues and form fluoride-containing mineral salts to enhance the anti-caries ability of teeth; on the other hand, fluoride can promote the deposition of minerals on the surface of teeth to remineralize the early caries and repair the tooth enamel. Since demineralization of teeth occurs throughout the decay process, multiple and local use of fluoride is recommended. The addition of fluoride in toothpaste can well meet the conditions of local and multiple use, and is the first choice to effectively maintain the appropriate fluoride concentration in the mouth. How much fluoride toothpaste is suitable to prevent tooth decay each time? A 60 kg weight adult, the recommended daily fluoride intake should be less than 4.2 mg. The fluorine concentration of adult toothpaste is generally 1000~1500mg/kg, if you use 1g of fluoride toothpaste (about 1cm long paste) and brush your teeth twice a day, the total amount of fluorine is only 2~3mg. By spitting out the toothpaste paste after brushing, most of the fluoride has been spit out, and the remaining fluoride swallowed into the body is only a very small portion, which will not cause harm to the human body. For children, especially those under 6 years old, due to their poor swallowing reflex, they are prone to swallow toothpaste when brushing their teeth, so care should be taken to prevent excessive fluoride intake. On the one hand, children should use children’s toothpaste that contains less fluoride (the concentration of fluoride is generally 250~500mg/kg) and not more than twice a day, and the amount each time should not exceed the size of a pea. On the other hand, parents should supervise their children to brush their teeth and encourage them to spit out the toothpaste and not to swallow it. Occasional swallowing should not be too much of a concern because even with toothpaste containing 1,500 mg/kg of fluoride, a 1-year-old child would have to take 33 grams at a time to reach a potentially toxic amount. The U.S. Centers for Disease Control and Prevention also recommends that fluoride toothpaste be used only after a young child reaches the age of 2. Fluoride toothpaste is not for everyone? The Oral Health Guide for Chinese Residents suggests that the promotion of fluoride application is suitable in low fluoride areas, moderate fluoride areas, and in high-risk populations in areas with a high incidence of caries. However, people in high fluoride areas are not suitable for using fluoride toothpaste. Long-term excessive intake of fluoride causes chronic poisoning. Mild poisoning will cause dental fluorosis, and very few severe poisoning will lead to fluorosis bone. Patients with dental fluorosis will have chalky spots or even pitting on the tooth surface, which turns yellowish brown due to dentin exposure and staining. What diseases can fluoride cause? Dental fluorosis is just one warning of fluoride. What is more frightening is that long-term intake of high doses of fluoride can lead to cancer, neurological disorders, and malfunction of the endocrine system! Since fluoride is found primarily in the bones, bones are the best tissue for scientists to look for fluoride imprints. Many studies with osteoporosis patients have shown that high doses of fluoride stimulate osteoblast proliferation, also in older patients. The exact mechanism is not known, but scientists speculate that fluoride produces these effects by increasing the concentration of tyrosine phosphorylated proteins (involved in the process of transmitting biochemical signals to osteoblasts). While fluoride may increase bone volume, bone strength is significantly reduced. Epidemiological studies and animal studies have shown that chronic intake of high doses of fluoride can make people more susceptible to fractures, especially the elderly and diabetics. The “fluoride danger theory” is still controversial in the scientific community. Even so, nine of the 12 members of the NRC panel agreed that people who have been drinking water with fluoride levels above 4 mg/L for their entire lives are definitely more likely to suffer fractures than healthy people. They also noted that low concentrations of fluoride may also increase the odds of fracture, there just isn’t enough evidence to prove it. When the children involved in the trial reached puberty, Levy hoped to reveal a link between fluoride intake and bone health by analyzing their spine, hip and whole-body bone strength. 2007, he collected some initial data, however, based on the amount of fluoride consumed by the subjects in early childhood, Levy did not find any difference in mineral content in the bones of these 11-year-olds. He insisted, however, that differences in mineral content may gradually emerge with age. The bigger controversy about fluoride is whether the biochemical reactions that occur in the bones and teeth mean that fluoride also affects the function of other organs and causes more disease. Currently, the debate is over osteosarcoma – the most common type of skeletal tumor, and the 6th most common of all childhood tumors in children. Because fluoride promotes the proliferation of osteoblasts, some scientists therefore believe that it is the massive proliferation of osteoblasts that leads to malignant tumors.