While in Texas last week, I broke a lobe off a crown on one of my molars. My dentist squeezed me in between appointments today and said we will have to remove the old crown and replace it with a new one. (Insert dollar-shock emoticon here.) He kindly ground down the part of the crown remaining which was cutting my tongue every time that member snaked over to touch the wreckage, which it did frequently, pretty much of its own volition). The dentist referred to the sharp edge as "broken glass." I asked why "glass" and he said that "procelain is a kind of glass." Never heard THAT before.