T.L.
my daughter has a huge oral fixation also her happens to be associated with her sensory intergration dysfunction. but because of that we where able to see a speech therapist which helped us a ton. some of the things that have helped is getting her to be aware of whats in her mouth so we use diffrent baby teether with lemonade powder or pixie stick sugar on them an let her chew on them to fell the diffrent tasts and textures. when we finished with this then we got her some chewy tubes so she always had something around her neck to chew on. She is now 9 and a HUGE gum chewer. You are truly wanting some help I would try to contact a speech therapist just to get some more Ideas on how to help him. Good Luck