Hydrodynamic Theory
Why should certain teeth in certain people become hypersensitive? This question was elegantly answered by a set of facts and suppositions that collectively became known as “the hydrodynamic theory.” While this theory is not yet regarded by all as completely factual, it explains most of the available clinical observations and anatomical realities.
The first component of the theory is the observation that dentin is normally covered by cementum or enamel. When this covering is in place, the teeth are not hypersensitive. However, when cementum or enamel are absent due to erosion, abrasion, dental manipulation or a tooth defect, dentin is exposed.
The second part of the theory focuses on the dentinal tubules, which are open at the surface of the dentin, allowing a direct channel to the nerve pulp. Supposedly, any of the abrasive or erosive forces that expose dentin also open these tubules to the oral interior. When any trigger is present, the tissue fluids inside the tubules move slightly inward or outward. Cold causes the tissue fluid volume to shrink slightly, and heat causes it to expand. Strongly osmotic sugar or sour solutions cause fluid to be drawn out of the tubules. An air blast on the tooth (by a dental instrument) dries a tiny portion of fluid at the distal end of the tubule, causing a significant outer flow of fluid in the tubule. Touching the tooth with a dental instrument or periodontal cleansing aid forces a small amount of fluid into the tubule. Intratubular fluid shifts are interpreted as pain by the Tomes’ fibers and/or central nerve root of the tooth.
