Why do you take an X-ray after filling a tooth?

I do commonly take one bitewing xray after filling a tooth in which the proximal(side next to the adjacent tooth) surface is restored. This will show me some relevant information. It helps me visualize the proximity of the filling to the pulp and to see if the tooth is filled without any voids,gaps or overhangs. It also allows me to check the proximal contour(How the filling contacts the adjacent tooth).

Sometimes teeth that are filled are in need of a crown and the X-ray is used to send the insurance company, since it shows how much filling is in the tooth. Often that is one of the criteria an insurance company uses when deciding to allow or disallow a treatment plan for a crown.

Many dentists do not take this sort of check film,but choose to wait until the patient has his or her next check up films taken. This is certainly OK, but I usually choose to check at the visit I place a filling if I am placing a filling.