I’m glad you asked. First about the causes because without addressing all of the causes, treatment success will be of short duration.
Gum recede from excessive stress to the teeth and their supportive structures. For example, harsh brushing using hard unpolished bristles with improper techniques; tooth grinding or clenching (usually a response to mental and emotional stress); improper chewing causing jaw imbalance; and faulty and biologically incompatible dental materials causing the gums to recede. Usually the bone under the gums recedes first (the purpose of the gums are to cover and protect the bone) thus the gums recede covering the receding bone. If the stressors are eliminated there is a possibility for the bone (and thus the gum) to grow back. This regenerative process can be long one, and patience must be exercised.