Advance directives and the severely demented

Should advance directives (ADs) such as living wills be employed to direct the care of the severely demented? In considering this question, I focus primarily on the claims of Rebecca Dresser who objects in principle to the use of ADs in this context. Dresser has persuasively argued that ADs are both theoretically incoherent and ethically dangerous. She proceeds to advocate a Best Interest Standard as the best way for deciding when and how the demented ought to be treated. I put forth a compromise position: both ADs and the Best Interest Standard have roles to play in guiding the care of the severely demented.