Composite resins are mainly used in the front teeth, where a silver filling would be conspicuous. There are different types of cosmetic fillings currently available. The type used will depend on the location of the tooth and the amount of tooth structure that needs to be repaired. Increasingly, these fillings are now also being used on the back teeth. composites are hardened by shining an intense light (ultraviolet) on them for a specified period of time, usually around 40 seconds. The light instantly hardens these fillings. You can eat right away because the composite is instantly hardened and requires no setting time.