[3-4] tooth decay/ cavities 蛀牙
https://www.youtube.com/watch?v=oQrcmcP6bhs https://www.youtube.com/watch?v=wooYZCJI7WI https://www.youtube.com/watch?v=-ZcM1Z3Gf-M https://www.youtube.com/watch?v=T1Fnb4iVf-c https://www.youtube.com/watch?v=3Qvo1nIkQnM