If your gums have receded, then unfortunately, they are not going to grow back unless you have some complicated periodontal (gum) surgery, and this is only necessary in particular circumstances.
Recession as a result of brushing technique alone, generally isn't that much of a problem. The exposed root surface isn't covered by the strong enamel layer (containing no nerves), instead it is made of a series of tubes directly connected to the nerve and because of this, sensitivity is often an issue.
There is so much variation here- some people with extensive recession and exposed roots do not seem to have any sensitivity- yet in others, the exposure of even the smallest amount of the root can cause incredible sensitivity to hot and cold, sweet things and most certainly our ultrasonic scalers. Sensitivity from tooth brush abrasion can be dealt with in a few ways and is discussed in treating tooth wear
If you have just had treatment for periodontal disease
, the recession may indicate an area of healing. As the gum inflammation recedes, the root may become exposed but your pocket depth will have been reduced- cleaning will now be easier and more effective. This is a good sign! If you haven’t had any treatment and your gums are receding due to gum disease, the support for your teeth is being lost and you need to see a dentist to get this under control.