A 45 year old female patient returns to your clinic with complaint of food lodgement in interproximal area of 47. On intraoral examination, 47 is restored with mesio-disto-occlusal amalgam restoration. Which type of matrix is used for this preparation?

**Core Concept**
The question is testing the knowledge of matrices used in amalgam restorations, specifically in the context of a mesio-distal-occlusal (MDO) preparation. A matrix is a critical tool in dental restorations, helping to shape and contain the amalgam material, ensuring proper contour and occlusion.

**Why the Correct Answer is Right**
In the case of an MDO amalgam restoration, a **rubber matrix band** is typically used. This type of matrix is designed to fit around the tooth, providing a stable and accurate framework for the amalgam material. The rubber matrix band is flexible, allowing it to conform to the contours of the tooth, and is usually used in conjunction with a matrix band retainer to secure it in place.

**Why Each Wrong Option is Incorrect**

* **Option A:** The **rubber sheet matrix** is not suitable for an MDO restoration, as it would not provide the necessary support and stability for the amalgam material.
* **Option B:** A **matrix band retainer** is a tool used to secure the matrix in place, but it is not the type of matrix itself.
* **Option C:** A **rubber wedge matrix** is used for specific types of restorations, but it is not the correct choice for an MDO amalgam restoration.

**Clinical Pearl / High-Yield Fact**
When choosing a matrix for an amalgam restoration, it's essential to select one that provides the necessary support and stability for the material. A rubber matrix band is a popular choice for MDO restorations due to its flexibility and ability to conform to the contours of the tooth.

**Correct Answer: C. Rubber matrix band**

✓ Correct Answer: A. Automatrix