No, but they will encourage an open bite, which is when teeth move to make space for the dummy or thumb. They may also affect speech development. That's why you should avoid using dummies after 12 months of age. Thumb sucking and dummies won't cause permanent problems as long as the habit stops by the time your child gets their second teeth, but it can be a hard habit to break. Discourage your children from talking or making sounds with their thumb or a dummy in their mouth, and don't dip dummies in anything sweet, such as sugar or jam.