I had a retainer after ortho work, I wore this has advised, but after a few years was told by my dentist both sides of my molars at the back where the wire of the retainer fitted, had a little black spot, on x-ray it showed beginning of decay, so needed small white fillings on the inside just where the wire sat, I have never had a filling in my mouth ever, so feel very let down that a retainer could cause this, as I have been very very particular with hygiene cleaning etc. Any hints on what to do now, or how it could have been avoided.
Gay

I don't think it is anything to do with your personal mouth hygiene, its just that the retainer wire rubbed ever so slightly against the molars causing the enamel to deteriorate to the point that it became decayed. Nothing could have stopped it from happening.