Dummies 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 is why you should AVOID using dummies after the age of 1 year.
Thumb sucking and dummies will not cause permanent problems as long as the habit is stopped by the time your child gets their second teeth; however, it can be a hard habit to break.
Discourage your children from talking or making sounds with their thumb or dummy in their mouth and do not dip dummies into anything sweet such as sugar or jam.