i picked up a pack of heinz baby basic dummys the other day and after opening them found they had a bigger teat than the other ones i had bought daughter. (she is 7months). i have been buying a packet a fortnight so she has enough but they are expensive so had to space them out. my question is, can i use the bigger teat with my previous bought smaller teat ones interchangeably without causing any harm to my DD. in other words, do i need to buy more of the bigger ones and only use them?