Final answer:
The shiny surface of a dry polished dental amalgam results from the mercury content in the amalgam, which amalgamates with silver and other metals, providing a lustrous finish.
Step-by-step explanation:
The shiny surface on a dry polished dental amalgam is primarily produced by the component mercury in the amalgam. Dental amalgams typically contain about 50% mercury by weight and are combined with silver and other metals. Mercury's unique properties, including its ability to amalgamate with metals such as silver and tin, give dental amalgams their durable and shiny surface after polishing. Unlike zinc in copper (brass alloy) or carbon dioxide in water, dental amalgams rely on the mercury blended with silver, which polishes to a shiny finish.