The curve on a graph, first described by Robert Stephan in 1943, showing the fall in pH below the critical level of pH 5.5, at which demineralization of enamel occurs following the intake of fermentable carbohydrates, acidic liquids, or sugar in the presence of acidogenic bacteria. After consumption, there is an elimination of the acid and a return to normal saliva or plaque pH, at which point repair of any destruction of the enamel structure takes place (remineralization). Repeated intakes of fermentable carbohydrates cause the low pH to be maintained for longer periods, thereby not allowing remineralization to take place.
Stephan R. M., Miller B. F. A quantitative method for evaluating physical and chemical agents which modify production of acids in bacterial plaques on human teeth. J Dent Res 1943;22:45–51.