I would need to see it. The 'ridges' on a coin is what's called reeding, and it is created by the collar die. There is the hammer (top), anvil (bottom) and collar.
If a dime planchet (coin blank) was struck without the collar, there would be no reeding, but there would also be nothing to hold the metal in place under the pressure of the other two dies. Metal would flow outward, and as a result, the coin would not only be misshapen, but it would lack the same detail on both sides that a normal coin has. This would be a very noticeable error.
The cent and the nickel are the only two coins where the collar die adds no reeding; you get a smooth edge. This sounds like what you're seeing. However, this is impossible. A coin blank for a dime could accidentally end up in the cent or nickel dies, but it would look like a cent or a nickel struck on a dime blank. For it to look like a dime, it had to be struck using the dime dies.
So I am at a loss for what you have, except to suggest that the reeding was machined off by someone after the dime left the Mint. That would be a damaged coin with no collector value.
That's why some good pictures would help. Both sides and turned sideways so I can see the edge.