My oldest had a dummy till about 6 months also and she would also scream at bed time unless she had it. It too was the only time I gave it to her except if she started to cry a lot when I was not able to pick her up straight away. I was able to get rid of the dummy by allowing a small amount of crying at bed time and then popping the dummy in if she started to get worked up and she would drop straight off to sleep at that point. If I gave her the dummy any earlier she would still cry and would spit out the dummy so I was going back and forward putting it in again. Eventually she didn't need it anymore but still cried a little at bed time till about 13 or 14 months. I figured she just needed to sook a bit to get off to sleep as nothing else I did seemed to help her nod off.
My youngest is 4 months and has the dummy a lot more than my oldest as she has always needed to suck a lot more for some reason. The Lactation Consultant I saw said that a dummy does not interfere with teeth as long as it is gone by 2 years of age. So if you aren't too concerned about your baby having a dummy then you have quite a while before it needs to go. I am going to let my daughter have the dummy as long as she has the need to suck for comfort up until she is walking and then look at taking it away then.
This probably hasn't helped much!! Good Luck with it, I hope someone else has some more suggestions!
4 lovely munchkins DD 10/03, DD 03/05, DS 10/06 &