its called gums recession which is generally happen by prolonged deposition of tarter. that are sign of gums disease which is also known as pyorrhoea. deep cleaning is necessary. some time gums surgery also needs to carried out to clean everything from the root surface.if the receding gums are less there we can do soft tissue grafting but that is possible or not that is decided by gums specialist only. so start with basic procedure first than further treatment needs to done.