Fluoride , hardening tooth enamel. 氟化物 ， 硬化牙齒琺瑯質。

Rubbing toothpaste on your teeth 'quadruples protection against decay' | Mail Online
http://www.dailymail.co.uk/health/article-2120960/Rubbing-toothpaste-teeth-quadruples-protection-decay.html
這種牙膏安全嗎？--KingNet國家網路醫院 | Second Opinion WebHospital
http://hospital.kingnet.com.tw/essay/essay.html?pid=21291&category=%B9D%C5%A5%A4%A3%B6%EE%BB%A1