## Core Concept
The functional cusp bevel is a critical concept in fixed prosthodontics, particularly in the fabrication of occlusal surfaces for dental restorations. It refers to the adjustment or shaping of the occlusal surface of a restoration to ensure proper occlusal function and harmony with the opposing dentition. This adjustment is essential for maintaining the health of the temporomandibular joint (TMJ) and the overall success of the dental restoration.

## Why the Correct Answer is Right
The correct answer, , involves understanding that a functional cusp bevel is primarily given for **non-restorable cusps**. When a tooth is heavily decayed or damaged, and a cusp is not restorable, a functional cusp bevel is used to adjust the occlusal surface of the restoration. This adjustment ensures that the restoration does not interfere with the occlusion and allows for smooth functioning of the jaw. The bevel helps in distributing the occlusal forces effectively and prevents the restoration from acting as an obstacle to the opposing tooth.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because cusps that are **restorable** do not typically require a functional cusp bevel. Restorable cusps are usually covered and supported by the restoration material to maintain tooth integrity.
- **Option B:** This option is incorrect as it does not accurately describe the primary purpose or scenario for applying a functional cusp bevel.
- **Option D:** This option is incorrect because it does not relate to the common practice or indication for a functional cusp bevel in dental restorations.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **functional cusp bevels are critical in ensuring proper occlusion and preventing TMJ disorders**. They are particularly important in cases where the occlusal scheme needs to be adjusted to accommodate a dental restoration. Clinicians must carefully evaluate the occlusal relationship and adjust the restoration accordingly to avoid complications.

## Correct Answer Line
**Correct Answer: C. non-restorable cusps.**