The confused baby
Sucking at the breast is fundamentally different from sucking from an artificial teat, which can lead to confused sucking behaviour in some babies. After sucking on an artificial teat or a dummy these babies are no longer able to suck from the breast, or no longer able to do so effectively.
The younger the baby, the greater the risk that she will not be able to alter her sucking behaviour again. This is why some hospitals prefer not to use bottles for additional feeding unless absolutely necessary, often using special containers e.g. Easy Cup as an alternative if required.
If a dummy is used to delay breastfeeds the baby satisfies her need to suck by sucking on the dummy. This means she sucks less at the breast and may be at risk of getting too little milk. Supply is regulated by demand so the process has a negative effect on supply. It is therefore helpful to avoid using a dummy for at least the first 4 to 6 weeks when milk production is building up.