辛达托福代报考位：到2017年9月7日上午托福官网没有释放考位，在此提醒广大考生抓紧时间报名，注意自己的考试时间，如对托福报名有任何疑问，欢迎咨询在线客服

　　Mechanism

　　Fluoride compounds are found naturally in the ground water in some regions, such as Colorado.[22]. Fluoridation chemicals are typically added to potable water in the form of sodium hexafluorosilicate or hexafluorosilicic acid (also known as hydrofluorosilic acid or fluorosilic acid).[23][24] This acid is largely a byproduct of phosporic acid磷酸 plants which process phosphate rock.[25] Since 2005, reduced phosphate processing has led to an increase in the price of fluorosilic acid, with one community seeing a 105% price increase in the past two years.[26]

　　[edit] Efficacy, effects, and cost-benefit analysis

　　When used appropriately, fluoride use is a safe and effective way to prevent and control dental caries蛀牙, and has contributed to dental health worldwide of both children and adults.[1] The recommended dosage of fluoride for humans from the CDC is 0.7 ppm to 1.2 ppm depending on the average maximum daily air temperature of the area. Fluoridation is intended to reduce tooth decay, with its associated health problems, at a low cost. Fluoridation of the public water supply is the "most equitable, cost-effective, and cost-saving method of delivering fluoride to the community." [27] In 2001, the US Centers for Disease Control and Prevention stated, "Although solid data on the cost-effectiveness of fluoride modalities alone and in combination are needed, this information is scarce."[1] A 1989 workshop on cost effectiveness of caries prevention concluded that water fluoridation is one of the few public health measures that saves more money than it costs to operate.[1] A 2000 comprehensive systematic review of the evidence stated that "it is surprising to find that little high quality research has been undertaken". The review found that fluoridation was associated with a decreased proportion of children with cavities (the range of mean decreases was 5% to 64%, the median 14.6%), and with a decrease in decayed, missing, and filled primary teeth (the range of mean decreases was 0.5 to 4.4 teeth, the median 2.25 teeth). It also found that at a fluoride level of 1 ppm an estimated 12.5% (range 7% to 21.5%) of people would have fluorosis they would find aesthetically concerning, and that there was no clear evidence of other adverse effects.[28]

大家在进行托福备考的同时，如果对考位方面也比较紧张，可联系辛达代报为您服务