A bite-wing x-ray (generally) consists of four x-rays showing the upper and lower molars and pre-molars.
As you can see from the above photo, it is important because it clearly shows areas of decay (which appear darker) interproximally (between the teeth) as well as in more exposed areas.
It also can show cavities just breaking through the dentin, which enables the dentist to diagnose and treat decay before it becomes larger or causes any problems.
Bite-wings can also show areas of tartar build-up and may reveal chronic infections that would remain undetected without this procedure. The bite-wing x-ray remains one of the most powerful tools in keeping your mouth healthy and pain free.