Which has least density?
**Core Concept**
Dental amalgam is a mixture of mercury, silver, tin, and copper used as a restorative material. The density of dental amalgam is influenced by its composition, with mercury contributing significantly to its overall density.
**Why the Correct Answer is Right**
The correct answer is that dental amalgam has the least density among the options. This is due to the high atomic weight of mercury, which is the primary component of dental amalgam. Mercury has an atomic weight of 200.59 g/mol, which is significantly higher than the other metals present in dental amalgam. As a result, dental amalgam has a lower density compared to the other options.
**Why Each Wrong Option is Incorrect**
**Option A:** Gold has a high atomic weight and is often used in dentistry for its biocompatibility and durability. However, its high density makes it an unlikely candidate for the correct answer.
**Option B:** Tin has a relatively low atomic weight and is used in dental amalgam as a corrosion inhibitor. However, its density is higher than that of dental amalgam.
**Option C:** Copper has a high atomic weight and is used in dental amalgam to improve its corrosion resistance. Its density is similar to that of gold and is higher than that of dental amalgam.
**Clinical Pearl / High-Yield Fact**
Dental amalgam has a density of approximately 10-11 g/cm³, which is lower than that of most other metals used in dentistry. This lower density makes it more prone to wear and tear, but also allows for better adaptation to the tooth structure.
**Correct Answer: D. Dental amalgam**