White, tooth colored, or composite fillings are placed on a tooth that has a cavity, is chipped, worn, or has abrasions.
Composite fillings are the standard treatment of tooth decay as most patients prefer not to have the amalgam (silver) fillings for the fear of mercury poisoning or the visual look.
It's normal to experience sensitivity to cold and hot after a composite filling. The discomfort should subside soon after.
To protect these fillings you should practice good oral hygiene and see your dentist regularly.