In normal (non-anesthetized) patients, Gysi (1900) reported that fluid distortion on the cavity floor caused sharp pain. Brännström et al. (1966, 1969, 1976, 1979, 1980, 1996) demonstrated dentin hypersensitivity (sharp pain) is the result of rapid fluid movement in the tubule complex, aggravated by aggressive air-drying. Physiological testing in various animal studies (Heyeraas 1985, Narhi 1983, 1985) confirmed the fluid pulsing or hydrodynamic mechanism (Brännström 1966) as the prime cause of sudden dentin pain. Physiologically, any rapid bi-directional fluid flow is the result of a sudden shift in tubule fluid from stimuli (i.e. cold or rapid airflow; Brännström 1996).