Figure 1. Relation between the Stephan pH challenge test and dental caries activity in maxillary and mandibular incisor plaque of subjects with different levels of caries activity. The challenge was a 10% (w/v) glucose solution administered as a rinse (25 mL) for two min, and the pH was measured with an antimony-rod touch-type pH electrode (adapted from Stephan, 1944, and reproduced from Kleinberg et al., 1982).