It's a baby tooth.

这是一颗乳牙。

If it is a lower baby tooth, throw it up onto the roof;

在日本，如果掉的是下牙，就扔到房顶上去；

In Mongolia, they put the baby tooth in the meat and feed it to the young dog.

在蒙古，人们把乳牙放在小狗的狗食中。

Take your child to the dentist within 6 months of the first baby tooth and no later than their first birthday.

在第一颗乳牙出现后6个月内就应该带孩子去看牙医，最迟也不能超过孩子一岁。

Proof of this can be determined by dropping a baby tooth into a glass of it, then going back the next morning to find most of it eaten away.

我们来终结这个流言：将一颗牙齿仍在可乐玻璃杯里，第二天早上回来发现大部分被蚕食了。