critical pH – The pH at and below which
demineralization of enamel occurs. The research
of Stephan and Miller originally demonstrated this
critical pH to be approximately 5.5 (see Stephan’s
curve). Due to other chemical factors, especially
the saturation of the immediate environment of
the enamel surface with respect to calcium and
phosphate, the presence of buffering agents, and
the fluoride availability, the critical pH may vary
and is considered to be between 4.5 and 5.5.