How many of us own traditional tooth mugs? Plastic, about the size of a cream slice, but semi-round with a straight edge. And creased, presumably a fashion statement. It's certainly a design issue - dirt, grease, and whatever else accumulates in impossible-to-clean crevices. Inside can be similar, particularly if you haven't washed it out for a while. So the top is secured by a plastic hinge, part of the overall structure and vulnerable. I think mine lasted quite a long time before becoming permanently detached.
I needed a new one. Not available except in chemists. I visited my local in Scarborough.
"Do you have a tooth mug?"
"Oh, okay then," and I turned towards the door.
I'd was nearly out on the street when the assistant called out, "Did you mean a denture bath?"