## Core Concept
The question pertains to the common complaints patients have following dental amalgam restorations. Dental amalgam is a widely used restorative material in dentistry, known for its durability and cost-effectiveness. However, like any dental procedure, it can be associated with certain post-operative complaints.

## Why the Correct Answer is Right
The correct answer, **D. Sensitivity to hot and cold**, is a frequent complaint because the process of placing an amalgam restoration can cause temporary irritation to the pulp, leading to sensitivity. This sensitivity is often due to the removal of decayed tooth structure, the mechanical preparation of the tooth, and the potential for microleakage around the restoration. The pulp's response to these changes can result in increased sensitivity to thermal stimuli.

## Why Each Wrong Option is Incorrect
- **Option A:** While sensitivity to sweet foods can occur, it is not as commonly reported immediately after amalgam placement as sensitivity to temperature changes.
- **Option B:** Pain on mastication (chewing) can occur but is less frequent as an immediate complaint compared to thermal sensitivity. It might be more related to issues like high restoration or occlusal problems rather than the material itself.
- **Option C:** A metallic taste is not a common complaint following amalgam restorations. Patients might experience a metallic taste with certain types of restorations or materials, but it's not the most frequent complaint with amalgam.

## Clinical Pearl / High-Yield Fact
A key point to remember is that post-operative sensitivity is a common issue after dental restorations, including amalgam fillings. This sensitivity is often temporary and can be managed with desensitizing toothpaste or other treatments. It's crucial for patients to report severe or persistent pain, as it could indicate a more serious issue like pulpitis.

## Correct Answer: D. Sensitivity to hot and cold.