All types of milk can cause cavities if they are inappropriately consumed. For example, cavities on the upper front teeth can develop if a baby with teeth is put to bed at night with a bottle of milk. However, plain cow's milk typically does not cause cavities if it is given in a cup with meals. Is milk at bedtime bad for teeth? Don't put baby to sleep with a bottle When babies fall asleep with a bottle some milk stays in the mouth and on the teeth. This can cause tooth decay.