**Question:** Due to inward or outward movement of dentinal fluid exciting the nerve endings

Core Concept: Sensitivity of teeth to cold, hot, or pressure, and the role of dentinal fluid in transmitting stimuli to nerve endings.

**Why the Correct Answer is Right:**

Correct Answer: D. Cavitation

Dentinal fluid, a mixture of fluid and dissolved salts, is present within the tubules of the dentin in the tooth. The movement of this fluid, due to factors like temperature changes or pressure, causes the dentinal fluid to either move inward (hypoosmotic) or outward (hyperosmotic) within the tubules. This results in the stretching or compression of the dentinal tubules, which then excites the nerve endings within the dental pulp, leading to the perception of sensitivity in response to stimuli like cold, hot, or pressure.

**Why Each Wrong Option is Incorrect:**

A. Sensitivity due to pulpal changes: This option is incorrect because sensitivity is primarily caused by changes in dentinal fluid movement within the tubules, not due to pulpal changes itself.

B. Sensitivity due to dentinal fluid movement: While dentinal fluid movement contributes to sensitivity, the primary cause is the stretching or compression of dentinal tubules, not solely the fluid movement itself.

C. Sensitivity due to pressure: While pressure can affect the dentinal fluid movement, the actual cause of sensitivity is the stimulation of nerve endings within the dental pulp, resulting from the inward or outward movement of dentinal fluid in response to pressure.

**Clinical Pearl:** An understanding of dentinal fluid movement is crucial for diagnosing and treating sensitivity issues in patients, as it helps identify the underlying mechanism of tooth pain and guides appropriate treatment options, such as desensitizing agents or restorative procedures.