@D1Doris,
A man lives his life more fully when he expresses his thoughts & feelings, strives for his dreams to become reality, rather than restraining all of these. The misconception here is that would give way to decadent pleasures & sadistic acts, perhaps. In living a life free from self-restraints, however, it means that we would understand what we really want to give ourselves real happiness. The acts of decadence or sadism etc. occur because we do not understand what gives us real happiness & think, initially, that those acts give us happiness.
The only way, hence, is by expressing our feelings & thoughts & realising our dreams, that we'd slowly find what gives real happiness. Dorian Gray was susceptible to the misconception modern man have, that it means to give way to every decadence on earth - but that's not a true form of happiness. So it seems that Dorian Gray's demise & macabre ending reaffirms our concept of the necessity of self-denial (when in actuality it merely reaffirms our misconception of a 'free life'.)
So in 'the mutilation of the savage', we destroy, or alter radically, the savage way of life, which refers to the old way of 'uncivilized' life including human sacrifices, & when we seemed more violent perhaps & narrow-minded - rather than merely piercings or tattoos. The mutilation of the savage, turning away from the savage part of us, has led to us turning to the other extreme of denying ourselves for fear of the savage in us emerging once again. The interpretation here is substantiated by the context, where he says, 'the bravest man... is afraid of himself', which means that he's afraid of the savage in him.