**Core Concept**
A diagnostic wax-up is a temporary, three-dimensional model of a patient's dentition, used to simulate the final restoration and visualize the esthetic outcome before fabricating the actual prosthesis. This technique is essential in restorative dentistry for planning and communicating treatment options effectively.

**Why the Correct Answer is Right**
A diagnostic wax-up is indicated when a patient requires a comprehensive treatment plan, involving multiple restorations, orthodontic treatment, or significant tooth reduction. This allows the dentist to visualize the final result, identify potential issues, and make necessary adjustments before proceeding with the actual restorations. The wax-up also serves as a communication tool between the dentist and the patient, helping to manage expectations and ensure a successful outcome.

**Why Each Wrong Option is Incorrect**
* **Option A:** A diagnostic wax-up is not typically used for simple fillings or minor restorations, where a more straightforward approach can be employed.
* **Option B:** While a diagnostic wax-up can provide valuable information, it is not solely indicated for patients with limited dental knowledge or those who require extensive education on their treatment options.
* **Option C:** A diagnostic wax-up is not a diagnostic tool in itself, but rather a planning and communication aid used in conjunction with other diagnostic tools.

**Clinical Pearl / High-Yield Fact**
A well-executed diagnostic wax-up can significantly reduce the likelihood of treatment complications, improve patient satisfaction, and enhance the overall esthetic outcome of the final restorations.

**Correct Answer: C.**