why you have to brush

Michael:  Kailey, it's time to brush your teeth.
Kailey:  why?
Michael:  because
Kailey:  so I don't get cavities?
Michael:  yes
Kailey:  what do you and mom call those black things on your teeth where you had cavities?
Michael:  fillings
Kailey:  you mean like when you are mad, or happy, or sad?
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