Final answer:
A gingival third restoration on tooth #3 is classified as a Class V restoration. Amalgam's advantages include cost-efficiency and durability, but its mercury content raises health concerns.
Step-by-step explanation:
An amalgam restoration located on the gingival third of tooth #3 would be a Class V restoration. Dentists use amalgams containing silver and other metals to fill cavities, including those on the gingival third. They choose amalgams for various reasons such as low cost, ease of manipulation, and longevity compared to alternative materials. Despite these advantages, the use of amalgams has been scrutinized due to their mercury content, which is approximately 50% by weight. Concerns about the toxicity of mercury have led to considerations for safer alternatives.