Figure 4. (a) Relation between time of eating and the pH of dental plaque in 18 different interproximal and facial/lingual dentition locations throughout the human mouth. Highest pH occurred in plaque in the mandibular interproximals of the lower incisors. Lowest pH occurred in the same sites of the upper incisors (see Kleinberg and Jenkins, 1964, for the specifics of the individual sites). Mean resting saliva pH was 6.7 (from Kleinberg, 1970b). (b) Range of pH of plaque on upper and lower approximal incisor surfaces in slower and faster salivary secreters. The dotted lines represent the mean resting salivary pH of the two groups (from Jenkins, 1979, based on data in Kleinberg and Jenkins, 1964).