**Core Concept**
The question is asking about a specific type of matrix retainer used in orthodontics, which allows for anatomical adaptation without the need for wedges. This concept is related to the design and functionality of orthodontic matrices, which are used to stabilize and guide tooth movement.

**Why the Correct Answer is Right**
The correct matrix retainer that allows for anatomy adaptation without wedges is the **Piggyback matrix**. This type of matrix is designed to adapt to the surrounding anatomy, allowing for more precise control over tooth movement. The piggyback matrix is typically used in conjunction with a bracket or a band to provide additional support and stability. The unique design of the piggyback matrix allows it to conform to the contours of the tooth and surrounding bone, making it an ideal choice for cases where anatomy adaptation is necessary.

**Why Each Wrong Option is Incorrect**
* **Option A:** The **Standard matrix** is a basic type of matrix retainer that does not allow for anatomy adaptation without wedges. It is typically used for simple cases and does not provide the level of precision and control required for anatomy adaptation.
* **Option B:** The **Closed-coil spring matrix** is a type of matrix retainer that uses a closed-coil spring to provide additional force and stability. While it can be used for some cases of anatomy adaptation, it is not the best choice for situations where precise control is required.
* **Option C:** The **Self-ligating matrix** is a type of matrix retainer that uses a self-ligating mechanism to provide additional stability and control. While it can be used for some cases of anatomy adaptation, it is not the best choice for situations where precise control is required.

**Clinical Pearl / High-Yield Fact**
One important thing to remember when choosing a matrix retainer is that the design and functionality of the matrix should be tailored to the specific needs of the case. For example, a piggyback matrix may be the best choice for cases where anatomy adaptation is necessary, while a standard matrix may be sufficient for simple cases.

**Correct Answer:** C.