The Collaborative International Dictionary of English v.0.48:

Demented \De*ment"ed\, a. [From Dement.]
   Insane; mad; of unsound mind. -- De*ment"ed*ness, n.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

dementedness \de*ment"ed*ness\ n.
   mental deterioration of organic or functional origin.

   Syn: dementia.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

dementedness
    n 1: mental deterioration of organic or functional origin [syn:
         dementia, dementedness]