He is currently using this one:

But he is constantly mouthing at it and licking it and just seems uncomfortable. His teeth have been done and checked, it the bridle is giving him that 'smile' But he opens his mouth and lowers his head and sometimes even gets the shanks in his mouth and then we will just stop and look at me, worried. He was abused in the past and I know bits bother him but the hackamore is bothering him even more and when I pull him up he throws his head and gets upset with stomping and dancing in place. But the bit keeps him calm and relaxed except for the mouthyness. Any Ideas on what bit I should use with him?
I was thinking maybe just a normal Snaffle bit, something mild?