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Problems arise when attempting to compare caries data collected in both Africa and the People's Republic of China. These difficulties are not only the result of differences in the criteria used for the diagnosis of caries but are also due to the diversity of cultural and social conditions existing within each of the geographical areas. However, interpreted with caution, the data seem to suggest that caries experience among children is still fairly stable and at a low level, in contrast to the predictions of a decade ago. When comparing data from adult and elderly cohorts, however, caries is seen to be a widespread disease with continuing slow progression throughout life.

The hypothesis that the Stephan pH responses of dental plaque would be different in caries-active and -inactive individuals was tested in 20 seven-year-old and 19 14-year-old Kenyan children. In each age group, half the children had ≥ 2 dentin cavities; the other half had no such lesions. With a palladium-touch microelectrode, interdental plaque pH was monitored between m1/m2 in each quadrant in the primary dentition and in the four molar/premolar regions in the permanent dentition. pH was also monitored in caries cavities in the occlusal surfaces of lower first molars and on the tongue. pH was measured before and up to 60 min after the children rinsed with 10 mL of 10% sucrose. Caries status of the individual was unrelated to plaque pH in comparable non-carious sites in both of the age groups. The pH minimum in the maxilla was about 0.5 pH units lower than that in the mandible. Active occlusal caries lesions had a resting pH value of about 5.5, about 1 pH unit lower than that of sound surfaces. The pH dropped to about 4.5 in caries lesions and recovered slowly. In sound occlusal sites, a pH drop to about 6.0 was followed by a relatively rapid return to the resting value. Thus, when the mean values were considered, the classic Stephan curve response was evident. However, when the pH changes at single sites were considered at various time intervals, a substantial, erratic fluctuation was observed. The tongue had a resting pH value of 7.0, which dropped to about pH 5.5 and remained low for more than 60 min.

The aim of this study was to assess the applicability of palladium touch micro-electrodes, connected to battery-run pH meters, for in vivo plaque pH measurements in children. The pH was assessed in 20 7-year-old and in 19 14-year-old caries-active and caries-inactive rural Kenyan children. The resting pH was measured at non-carious interproximal and occlusal sites and in open dentine cavities. Independent repeated measurements were performed at given sites at intervals of 15 s and 5 min and on different days. The resting plaque pH varied widely among the children, and there was no significant difference between caries-active and caries-inactive groups. The most striking feature was the considerable erratic fluctuations of pH at a given site with time, both in resting and in sucrose-challenged plaque. These fluctuations were sensitively recorded by palladium touch microelectrodes. After a sucrose rinse, not all sites in the same mouth behaved in a similar fashion, and thus the classical ‘Stephan curve’ was not always apparent. In conclusion, the palladium touch microelectrodes are highly applicable for plaque pH measurements in children, even under extreme field conditions.

In 5 rural Kenyan children, the effect of sugarcane chewing on plaque pH was compared with the effect of a mouthrinse with 10% sucrose at various intraoral sites. They all had poor oral hygiene and at least two carious cavities in occlusal surfaces of molars. pH measurements were conducted under field conditions using paladium touch microelectrodes connected to a battery-operated pH meter. There was a marked difference in pH response of non-carious approximal sites between maxilla and mandible, with the lowest values in the maxilla. However, the pH recovery following the instantaneous drop occurred in parallel even if most pH values had not returned to baseline values 30 min after the sucrose rinse. Following the sugarcane chewing, the pH fall was less pronounced on all sites, and within 5-10 min the values had returned to resting pH and even exceeded this. In carious cavities, a similar pattern was observed, although the acidity in these sites was more pronounced, also reflected in a lower resting mean pH. The main conclusion from this study is that sugarcane chewing yields a less pronounced pH drop and a quicker pH recovery in dental plaque than is seen following a mouthrinse with 10% sucrose. This difference probably results from stimulation of salivary flow associated with the chewing.

317 children born and raised in two rural areas of Machakos District in Kenya were examined for enamel changes. All sources of drinking water were monitored for F–– over a period of 1 year.

Children aged 11–15 years from three low-fluoride zones (< 0.5 ppm in drinking water) situated at sea level, 1,500 m and 2,400 m above sea level, and from two higher-fluoride zones (0.5–1.0 ppm in drinking water) were examined for dental fluorosis. In the low-F zones 36.4% of the children at sea level had dental fluorosis, as compared to 78.0% at 1,500 m, and 100.0% at 2,400 m. In the higher-F zones 71.2% had dental fluorosis at sea levels as compared to 93.8% at 1,500 m (p < 0.001). The intraoral pattern of dental fluorosis was similar in each of these five populations, and the severity of dental fluorosis of each tooth type increased significantly with increases in altitude in both the low and higher-fluoride zones (p < 0.001). Moreover the severity of dental fluorosis was associated with increases in fluoride concentrations at constant altitudes (at sea level and at 1,500 m). This study establishes for the first time that populations living at high altitudes may be more susceptible to dental fluorosis than those at low altitudes for a given concentration of fluoride in drinking water. The findings indicate that certain physiological changes may occur in humans living at high altitude whereby the effects of fluoride on mineralizing tissues become exacerbated.