By increasing the percentage of which metal, the strength and hardness of amalgam increases:

## **Core Concept**
The question tests the understanding of dental amalgam composition and its properties. Dental amalgam is a mixture of metals, primarily used for filling teeth. Its strength and hardness are crucial for its durability and effectiveness. The primary components of dental amalgam include silver (Ag), tin (Sn), copper (Cu), and mercury (Hg).

## **Why the Correct Answer is Right**
Increasing the percentage of **Copper (Cu)** in dental amalgam enhances its strength and hardness. Copper plays a significant role in improving the physical properties of amalgam. It forms a stronger and more durable alloy, which contributes to the longevity of the dental restoration. When copper content is increased, it helps in reducing the gamma-2 phase, which is a weaker phase in the amalgam structure, thereby increasing the overall strength and hardness.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Increasing silver (Ag) content does contribute to the strength of amalgam but not as significantly as copper in terms of hardness and durability against wear.
- **Option B:** Tin (Sn) is essential for the formation of the amalgam but does not directly contribute to increased strength and hardness when its percentage is increased beyond a certain point.
- **Option D:** Mercury (Hg) is a critical component for the plasticity and handling of amalgam but does not increase strength and hardness; in fact, excessive mercury can weaken the amalgam.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the addition of copper to dental amalgam not only increases its strength and hardness but also reduces corrosion and improves the overall clinical performance of the restoration. High-copper amalgams are known for their enhanced properties compared to low-copper amalgams.

## **Correct Answer:** .