I have seen this expression in a few threads so thought it warranted one of it's own.
My first ds was never going to get a 'dummy' and I sat for hours at a time with my pinkie in his mouth thinking that was superior, then he got his thumb.
My second ds was a thumbsucker but contracted meningitis at 6 months and couldn't suck his thumb because he was so ill. He was in pain though and his mouth was getting dry sucking my pinkie so I sent dh to buy him a couple of dummies - a yellow one and a green one. He looked really cute and more importantly got comfort from sucking.
My third ds was premature and I had bought dummies because I knew he would be in special care in an incubator. He didn't need them because he was on a ventilator for a week! When he did start feeding he was settled in between initially but when we got home I used it if I was too busy to breastfeed straight away. I stopped him at 8 months by not replacing it when it burst. He never did find his thumb.
My last baby dd also got a dummy because she was stuck in an incubator under phototherapy needing exchange blood transfusions due to incompatable blood groups. She stoppd about 9 weeks when she got her thumb.
Contraversially I much preferred the thumb sucking because they could find it themselves during the night. None of them have buck teeth by the way.
The point to this ramble is that some babies definately are comforted by sucking. As long as they are not restricted at the breast within the first few weeks and are fixing properly, there is no reason why they can't have a 'comforter' which is a much better term.