Composite filling (tooth colored) Dentists call natural looking white fillings, posterior composites. Until recently, dentists filled and sealed cavities exclusively using a silver and mercury amalgam. Unfortunately, these fillings (or restorations) often weaken teeth due to the large amount of the original tooth that has to be removed and have the disadvantage of causing the tooth to darken as they age. Modern dentistry has increasingly turned to composite fillings as a strong, safe and more natural looking alternative.

Wikipedia: Dental composite resins are types of synthetic resins which are used in dentistry as restorative material or adhesives. Synthetic resins evolved as restorative materials since they were insoluble, aesthetic, and insensitive to dehydration and were inexpensive. It is easy to manipulate them as well. Composite resins are most commonly composed of Bis-GMA monomers or some Bis-GMA analog, a filler material such as silica and in most current applications, a photoinitiator. Dimethacrylates are also commonly added to achieve certain physical properties such as flowability. Further tailoring of physical properties is achieved by formulating unique concentrations of each constituent.

The main advantage of a direct dental composite over traditional materials such as amalgam is improved aesthetics. Composites can be made in a wide range of tooth colours allowing near invisible restoration of teeth. Composites are glued into teeth and this strengthens the tooth's structure. The discovery of acid etching (producing enamel irregularities ranging from 5-30 micrometers in depth) of teeth to allow a micromechanical bond to the tooth allows good adhesion of the restoration to the tooth. This means that unlike silver filling there is no need for the dentist to create retentive features destroying healthy tooth. The acid-etch adhesion prevents microleakage; however, all white fillings will eventually leak slightly. Very high bond strengths to tooth structure, both enamel and dentine, can be achieved with the current generation of dentine bonding agents. The downside to composite when compared to amalgam is a shorter lifespan of the filling, and the high likelihood of requiring root canal therapy if the failure of the filling is not caught quickly. Amalgam fillings may crack a portion of the tooth off, but otherwise tend to fail at a much slower rate.