Rather than brush, i would slowly start using some toothpaste on a guaze pad until his gums start to heal. sometimes adults complain that flossing cuts their gums, but actually, their gums are inflamed which causes the bleeding and the answer is to take better care of their teeth. when they do, the inflamation subsides, and their gums stop bleeding which is why i suggested to start slowly with guaze pads. As his gums begin to heal and stop bleeding, then start adding a brush.