Leo Lichtman wrote:

But, how would a dentist use it? Wouldn't he have
to place his eye 2" from your mouth?

The mirror's focal distance seems to run between about 1-2" from
whatever you are looking at. I just ballparked the 2" from my eye. It
will still magnify clearly when held at much greater distances from the
eye, just needs to be close to what you're looking at. I'm not an optics
guy, can't explain the whys and whatfors, just know that it lets me look
at my own eyeball with exceptional clarity. I'd been using this when
machining in tight places. I'd asked my dentist about them. He says
they're back surface mirrors and distort the image slightly. He prefers
using front surface mirrors and those neat (but expensive) glasses with
the long standoff lenses. Sorta like a microscope you wear...

Jon