Well, it was a collection and you did pay it so it is technically accurate what is reporting on your credit report. I'm doubtful the CRA will delete it but you could contact the dentist since the dentist is the OC who reported it and ask him/her to have it deleted.
I think I disputed once or twice with the CRAs to no avail and have since begun to only dispute with the OC. I was able to get a few things that were inaccurate removed or updated that way.