Your gums might be receding due to so many factors; Congenintal thin gums, hard brushing, orthodontic treatment (braces), crown and etc. It can cause tooth sensitivity to cold and hot. Exposed roots are more vulnerable to decay, as they are not as strong as tooth crown enamel. The gold standard of care is to graft your own gums from the roof of your mouth to the affected area. The healing takes 10-14 days. Ask your hygienist if your gums are good or are experiencing a recession?