Sensory mechanisms in dentine: A literature review of light microscopy (LM), transmission microscopy (TEM), scanning microscopy (SEM) & electro physiological (EP) tooth sensitivity: Is the ciliary organelle on the odontoblast the elusive primary nociceptor?

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Ancient humans believed in myths-that tooth pain was due to evil spirits [1].Homer-the Greek author even wrote of tooth pain in his classical epics [2].The European renaissance-circa 1350 to 1600-attributed tooth pain to worms that were allegedly found in tooth lesions [3].Scientific methodology has described 3-theories of dentine sensitivity: (1) In 1770 Hunter suggested tooth sensitivity was due to pulpal nerves [4].(2) In 1842 Neill 1 st proposed that tooth sensitivity was due to fluid movement in the dentine tubules [5].(3) In 1856 J Tomes implicated odontoblast processes (OP's) in the dentine tubules as initiating tooth sensitivity [6].In 1899 Gysi reported that dentine sensitivity was clinically activated by fluid-flow in the dentine tubules [7].In 1968 Brännström proposed the hydrodynamic fluid-flow theory of dentine sensitivity [8].Using LM & TEM Mummary (1916), Tiegs (1938), Bernick (1948), Fearnhead (1961), Itoh (1976) & others observed nerve fibers in the predentine & dentine tubules.Using TEM Arwill (1967) described 8-sub-patterns of nerve fibers in the dentine tubules & Frank (1968atubules & Frank ( , 1972tubules & Frank ( , 1975)).Corpron & Avery (1973) observed nerve fibers extending ≈150µm from the predentine interface into the dentine tubules by TEM.Detailed LM, TEM & SEM studies-by Gunji-reported 4-nerve patterns in the predentine-dentine region.In 1958 Avery & Rapp reported acetylcholine receptors on odontoblasts.Some primate OP's have been shown to extend the length of the dentine tubule [9] & some cross the basement membrane of the enamel-dentine-junction (EDJ) as enamel spindles.All eukaryotic cells display cilia, which are classified as specialized motile or sensory organelles that mediate gradients of sensory perception e.g.pressure, fluid-flow, which perceive environmental stimuli.TEM studies show cilia-extending from odontoblasts into the dentine tubule-suggesting they may be the initial mechano-nociceptor of dentine sensitivity [10].