I'm not sure of the physics reason why, but X-ray images don't have the resolution. You would think they would because X-rays have a much shorter wavelength, but I think it has to do with the fact that you're dealing with a point source and relying on materials to absorb the X-rays. So, with an X-ray, what you're seeing are projected shadows some distance away from the thing you're imaging. Those shadows are also convolved with all the layers between the layer of interest and the sensor, so, you get all the metal layers interacting with the light making it even harder to see a single metal layer.

Thus to get a high resolution of individual slices, you have to do something like ptychograpy or CT scanning, where you move the light source around to get a better idea of what's doing the absorption. These types of scanners are substantially more expensive than a dental X-ray.