Cervical resorption after bleaching is prevented by:
80% alcohol drying immediately after bleaching
Alpha tocopherol applied immediately after bleaching
Sodium perborate + sodium hypochlorite
Sodium perborate + calcium hydroxide
Cervical resorption is usually painless, until the resorption exposes the pulp, necessitating endodontic therapy. Intracanal dressings of calcium hydroxide are often successful in halting further tooth resorption. 

Severe external root resorption often necessitates extraction of the tooth. 
Moderate root resorption can be treated by orthodontically extruding the tooth and restoring it with a post-retained crown, but the prognosis of this treatment can be doubtful. 
Mild cervical resorption can be treated by surgical access, curettage, and placement of a restoration.