Baby bottle tooth decay is caused by sugary substances in breast milk and some juices, which combine with saliva to form pools inside the baby's mouth. If left untreated, this can lead to premature decay of your baby's future primary teeth, which can later hamper the proper formation of permanent teeth. One of the best ways to avoid baby bottle tooth decay is to not allow your baby to nurse on a bottle while going to sleep. Encouraging your toddler to drink from a cup as early as possible will also help stave off the problems associated with baby bottle tooth decay.