"Composite resin" fillings (also called white fillings) are a mixture of powdered glass and plastic resin, and can be made to resemble the appearance of the natural tooth. Although cosmetically superior to amalgam fillings, composite resin fillings are usually more expensive. Bis-GMA based resins contain Bisphenol A, a known endocrine disrupter chemical, and may contribute to the development of breast cancer. However, it has been demonstrated that the extremely low levels of bis-GMA released by composite restorations do not cause a significant increase in markers of renal injury, when compared to amalgam restorations. That is, there is no added risk of renal or endocrine injury in choosing composite restorations over amalgams. PEX-based materials do not contain Bisphenol A and are the least cytotoxic material available.