There are two kinds of people in the world:
People who are willing to share their toothbrush and those who are not.
The people willing to share are generally better people. Perhaps not as wise or prudent, but better. More trusting and generous and relaxed.
I would share my toothbrush with my wife, my children, and almost anyone else I know.
It's also important to note that the Center for Disease Control and Prevention recommends that you never share your toothbrush under any circumstances. In some cases, sharing a toothbrush can lead to life threatening infections.
I guess Billy Joel was right. Only the good die young.