Well unless my 2 year old is a genius then I wouldn't say so
She has had a dummy since she was 6 weeks and is the biggest chatter box going. Can recite all the nursery rhymes and christmas songs. Clearly asks what she wants and forms sentences (sometimes says things which i didn't know she had learnt)
I do encourage her to take the dummy out during the day or when asking for things. I have also encouraged clear queens English, so I try not to use slang or baby talk with her.
I didn't realise this! I knew dummies could cause speech delay but I thought that's just if they used them in the daytime as it prevents proper babbling. My son only uses his dummy for night time... the overseeing muscles things has me worried! I guess using a dummy for night sleep is bad too?