Displacement of odontoblast nuclei into the dentinal tubules — the phenomenon known as aspiration — is caused principally by:

Correct answer: A. Desiccation of the dentine surface

• A. CORRECT. DESICCATION — most often from prolonged air-drying of freshly cut dentine — draws dentinal fluid outward through the tubules. The flow is rapid enough to pull odontoblast nuclei from the pulpal end of the tubule up into it. The displaced cells die, and the histological finding of nuclei sitting within tubules is termed odontoblast ASPIRATION.
• B. Bacterial invasion causes inflammation and eventually necrosis, not this particular displacement.
• C. Occlusal overload affects the periodontal ligament rather than producing odontoblast aspiration.
• D. Chemical irritants can injure odontoblasts, but the specific mechanical displacement of nuclei into tubules is a fluid-flow phenomenon.

Note: This is the hydrodynamic theory made visible. The same outward fluid flow that displaces the nuclei is what stimulates the A-delta fibres and produces the sharp pain of dentine hypersensitivity. Blot dentine dry; do not blast it with air.