C.B.
I think they are used for different things. Something that looks like a retainers can widen the palate (palate spreaders) but they do not have the same ability to move teeth like braces. I had all of them: palate spreaders and then true braces that moved some of my teeth as much as10mm (the space of a whole molar). I also wore head gear to move the rear molars back to make more space on my jaw for my teeth. After braces were done I got retainers to "retain" the teeth in the same position. If you do not wear retainers teeth can move out of alignment again. Now there are those invisalign braces that look clear, but those are also expensive.