Final answer:
A composite resin is a tooth-colored substitute for amalgam used in dental fillings, preferred for aesthetic reasons and because it does not contain mercury.
Step-by-step explanation:
A composite resin is a tooth-colored material often used in place of amalgam for filling cavities. While dental amalgam is a cost-effective and durable material composed of a mixture of metals, including approximately 50% mercury, concerns have been raised about its safety due to mercury's toxicity. In contrast, composite resins are aesthetically more pleasing and do not contain mercury, making them a popular choice for patients. They may not always be as durable as amalgams, but advancements continue to improve their longevity and strength.