Cotton balls? Never heard that before, how many did you feed the dog and what breed/age is said dog?
Wonder Bread went out of business, so get a loaf of cheapo White with lots of preservatives. Wonder Bread is the standard remedy for sharp pica as it clumps around it. Feed the dog as much dry bread as he wants. When he doesn't want any more feed him a few more slices with peanut butter on them.
You got most of the glass up and it was probably only a few slivers, if anything. If dog's teeth, lips, gums are not bleeding and do not have adhered glass he may not have eaten any of it. What was in the glass that might've attracted a dog? Dog might've looked guilty just because something broke, everyone was upset, and he thought he might be in trouble for something.
Dogs are TOUGH and their intestines are thick, wide, and straight. They can eat all sorts of crazy stuff that would kill a person. Dog will probably be fine.