Thanks. I'm greatly reassured my posts I saw like this. I've been OP'ing now for about three months and honestly came close to beliving that it was breaking down, rather than helping, my mouth. I simply think it exposes weaknesses, and you're right, it obviously can't reach inside a sealed tooth. So all is well. The crown is fine, the old piano teacher smell has gone, and my worries have evaporated with it.