teether and pacifier are different and you can go through the difference by searching internet. there is no problem in using pacifier / nipple / teether if cleaned. the problem arises when it falls down and goes again inside the oral cavity of the child without proper cleaning and sterilization. if it is not cleaned and goes in the oral cavity can cause infection and cough and cold and loose motion you can use them to sooth the gums as well as calm the child but yes if it not cleaned properly and regularly or when it falls down then it definitely can cause infections