Bleaching tetracycline-stained teeth is difficult, some clinicians advocate intentional endodontic therapy along with the use of an intracoronal nonvital bleaching technique to overcome this problem. Although the esthetic result appears much better than that obtained from external bleaching, this approach involves all the inherent risks otherwise associated with endodontic treatment. External bleaching techniques offer a safer alternative, although they may not be as rapid or effective.  Patients who have darkly stained teeth always should be informed that although porcelain (or composite) veneers can result in improved esthetics, they may not entirely eliminate or mask extremely dark stains. Because of the limited thickness of the veneers and the absolute necessity of incorporating intrinsic opacity, the realistic translucency or esthetic vitality of veneered teeth may never be comparable with that of natural, unaffected teeth. Full porcelain coverage with all-ceramic crowns may be indicated in some patients with severe discoloration because of the crown’s greater capacity to restore esthetic vitality. Reference- Sturdevant 7th ed Pg-281