Minor dings in bare wood can often be popped out by applying a bit of boiling water, which will swell the grain. If water doesn't work, try heated acetone. Place a small container of acetone in a large container of hot water to heat it, away from any ignition source. Steam will also work - to fix up large areas, use an iron on low over a damp towel. I have even gotten the hot water trick to work through a finish, but there is no telling what the result may be, and I don't recommend trying it.