Resin composite fillings are made of ceramic and plastic compounds. Because resins mimic the appearance of natural teeth, these fillings have been used in front teeth for years. When they first appeared, however, resin compounds weren't strong enough to be used in back teeth, where high-pressure grinding and chewing require greater durability. In the past 10 years, technology has improved enough to allow the use of resin material in posterior or back teeth and make for a very natural looking smile.