Many parents use a dummy as a way of comforting their baby, especially if you're trying to get him or her off to sleep. Limited use of dummies is fine, but if your child sucks on a dummy for long periods, it could cause problems in the way the teeth develop. The same is true if your baby sucks his or her thumb. The pressure of the thumb or dummy against the back of the teeth could push them forward, which may mean your child will need corrective treatment - like a brace or having teeth removed - later on.
Try to wean your child off sucking its thumb or a dummy, treating it as part of the growing up process. Never be tempted to dip your child's dummy in anything, especially something like sugar or fruit juice. Prolonged contact with the teeth could cause real damage.