## Core Concept
The question pertains to the principles of restorative dentistry, specifically the management of old restorative materials. The decision to remove old restorative material is crucial and depends on several factors including the condition of the restoration, the presence of caries, and the overall health of the tooth.

## Why the Correct Answer is Right
The correct answer, , implies that old restorative material should be removed if there is a secondary caries (tooth decay around or under the restoration). Secondary caries is a significant reason for the failure of dental restorations. When caries develop around or beneath an existing restoration, it indicates that bacteria have penetrated the interface between the tooth and the restoration, leading to demineralization of the tooth structure. Removing the old restoration is often necessary to assess the extent of the caries, remove the decayed tooth structure, and place a new restoration that can properly seal the tooth and prevent further bacterial invasion.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because not all conditions require the removal of old restorative material. For example, if the restoration is still intact, properly sealed, and there's no evidence of caries or other complications, it might not need to be removed.
- **Option B:** This option is incorrect as it does not provide a clear or specific condition that would necessitate the removal of old restorative material. The presence of a fracture might not always necessitate removal; it depends on the location and extent of the fracture.
- **Option C:** This option is incorrect because the mere presence of an old restoration does not automatically necessitate its removal. Many old restorations can remain in place for years without causing problems, provided they are regularly monitored for signs of failure.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the decision to remove an old restoration is often guided by clinical and radiographic findings. Secondary caries is a major indication for removal, as it directly threatens the health of the tooth. Regular check-ups can help identify issues early, potentially saving the tooth from more extensive damage.

## Correct Answer: D. Secondary caries.