## Core Concept
Internal resorption is a pathological process that occurs within the dental pulp, involving the breakdown and removal of dental hard tissues, such as dentin, by cells like odontoclasts. This process is often associated with pulpal necrosis or chronic inflammation. Understanding the characteristics of internal resorption is crucial for dental diagnosis and treatment planning.

## Why the Correct Answer is Right
The correct answer, ., describes a key feature of internal resorption. Internal resorption is characterized by the presence of resorptive lacunae or areas of dentinal resorption within the root canal, which can be visualized radiographically as a widening of the canal or a scooped-out appearance of the dentin. This process is usually painless and discovered incidentally during radiographic examination. The resorption is often caused by the activity of odontoclasts within the pulp.

## Why Each Wrong Option is Incorrect
**Option A:** This option does not accurately describe a characteristic feature of internal resorption. Without specifics, it's hard to directly refute, but typically, internal resorption is not primarily about external root resorption or surface changes.

**Option B:** This option might relate to another dental condition or a nonspecific description that does not uniquely identify internal resorption.

**Option C:** While certain dental conditions can present with radiolucencies or changes in bone density, the specific pattern and location of internal resorption are distinct.

## Clinical Pearl / High-Yield Fact
A key clinical pearl for internal resorption is that it often presents **asymptomatically** and is discovered on routine radiographic examination. Early detection can prevent extensive tooth destruction. Clinicians should consider internal resorption in the differential diagnosis for teeth with a history of trauma or pulpal pathology.

## Correct Answer Line
**Correct Answer: D.**