I've been a dental ceramist for the last 22 years. I've spent the last 14 years working pretty closely with a couple of specialists, actually participating in case planning and being chairside during procedures. I don't see any pottery glaze in your picture. The "part that widens out" is the "crown" of the tooth, & should be covered with shiney enamel (underneath that is dentin, then pulp, then nerve). The root portion of a tooth doesn't have enamel. The material that makes up the exterior surface of the root is called "cementum", and can be fairly rough on an extracted, dried tooth. It's hard to tell how big your tooth is in the picture. From the pictured lingual surface (the tongue side), it looks like it flares a little too much to be human, I'm thinking a barnyard animal. If the picture was of the labial surface (the side that contacts the inside of the lip), it would be a lot easier to identify it.
Anyway, the picture looks like a real tooth.