EternalBrick

Did you use a new toothbrush? Dried toothpaste sticks horribly to everything. If you want to clean that off, put them under hot water and scrub vigorously with a new toothbrush. It should get most of the gunk off, and the plastic shouldn't be damaged by the brushing.

I'm not familiar with that particular one, but I've had similar problems with other headgears. This should work for just about any headgear: Remove the head and headgear from the body. Grab a hairpin or similar implement. Insert the looped end of the pin into the head until it touches the inside curve of the head. Grab the headgear in your other hand and pull the two apart, keeping the pin against the inside of the head. The head should pop right out. Failing that, try opening a loop on a paper clip enough to be wider than the hole - probably squished into a triangle - and wedge it in. That will let you pull the head equally from both sides.