If you havnt read about metabolic bone disease and its causes, please google some info. It is the leading cause of receeded jaw lines.
Also make sure you get a good mercury vapor bulb UVB for him to heal and grow stronger bones. Natural outdoor sun is the best when able. Remember UVB can not pass thru plastic , glass or fine screen.
The picture is of one of my rescues and as you can see his mouth is MESSED up. I feed him in a low dised cake pan. He has trouble with some foods and i have to pile stuff up high and fluff it up and then use a cheese grater for addition fruits and veggies. One thing he has no trouble with is being fed banana, i peel it and point the end at his mouth and head it til its to short to hold lol.