歯につきにくい

I recently got a pack of gum in a treat box from Japan. One of the phrases on the front was "歯につきにくいガム" which I understood to mean something like "gum that's difficult to pierce with your tooth/teeth" so hard gum as opposed to soft gum. I've seen the "につきにくい" in other places though where that meaning doesn't seem to fit. Am I not understanding this phrase correctly?

"stick to", not "pierce". You're looking at the wrong つく

Ah! That makes a lot more sense.