Frequently when I examine patients suffering from food trapped between their teeth or bleeding gums, I find restorations with an overhang. 
As seen on the right an overhang is an excess of dental filling material that projects beyond the margin of a tooth. It leads to food being trapped under the ledge giving an idea hideaway to bacteria since it is very difficult to clean. As seen in the image on the lower left, the gums swell and only after my professional cleaning, the amalgam excess became evident on the lower right. But the overhang needs to be removed to achieve a complete resolution of the food trap.
Overhangs can be created not only from fillings, but from poorly fitted crowns, veneers or excess of dental cement. It is important to have the excess of dental material removed to prevent further damage to the tooth or the supporting bone from decay or gum disease.
If you find that there is an area where food always remains after eating, you may have an overhanging restoration. Please make an appointment for me to check it.