**Core Concept**
Overdentures are a type of removable partial denture that is supported by natural teeth roots, either retained roots or implants. This treatment option is chosen to preserve as much of the patient's natural dentition as possible, while also providing support and stability to the denture.

**Why the Correct Answer is Right**
The primary reason for choosing overdentures over complete dentures is to maintain the remaining natural teeth roots, which provide a more stable and secure base for the denture. This is achieved by distributing the forces of mastication more evenly across the remaining teeth, reducing the stress on the denture and the surrounding tissues. Additionally, overdentures can help to prevent bone resorption, which can occur when teeth are missing, and preserve the facial aesthetics of the patient.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because retained roots do not necessarily provide a stable base for the denture, especially if they are loose or mobile. Overdentures are indicated when there are at least two retained roots that can provide sufficient support and stability.
**Option B:** This option is incorrect because complete dentures are often chosen when there are no remaining natural teeth roots, making overdentures a less viable option. However, in cases where retained roots are present, overdentures are preferred over complete dentures.
**Option C:** This option is incorrect because while bone resorption can occur with missing teeth, overdentures are chosen to prevent bone resorption by preserving the remaining natural teeth roots and providing a stable base for the denture.

**Clinical Pearl / High-Yield Fact**
A key consideration when choosing between overdentures and complete dentures is the presence of retained roots that can provide sufficient support and stability to the denture. A minimum of two retained roots is typically required for overdentures to be a viable option.

**Correct Answer:** C.