Receeding Gums

I have about 4 teeth where the gums are receeding pretty badly. The root is starting to get exposed and is very sensitive. I actually have very healthy teeth and gums otherwise. My dentist wants to bond a composite material over the exposed root area to keep the receeding from going further. I had all of my mercury fillings replaced a few years ago and do not want to put something harmful back in my mouth. Do you think this would be ok/safe?

BTW, I tried oil pulling and it had no effect on the receeding gums.