In the case that your gums have withdrawn and you now have bare root areas – you have the condition - Gingival Recession.
What is at stake is not merely aesthetics, but sensitivity, or even pain, to changes in temperature as well as to touch and certain other stimuli.
Gums cannot grow back on their own so surgical intervention is required. This entails an operation that will return gums to their original position, or transplant it over the bare root from some other position, most often the palate.