THE dental caries experience rates of Evanston school children, aged 12, 13, and 14 years, indicated a reduction of 12.19 per cent after these children had been exposed to artificially fluoridated water for a period of twentythree to thirty-four months.1This report on the dental caries experience rates is for children of the same age, presumably influenced by the same conditions, but with exposure time to fluoridated water increased from twenty-three to thirty-four months to fifty-nine to seventy months at the time of dental examination.
METHODThe mechanism of the study, with the exception of the material pertaining to rates per hundred teeth and rates per hundred surfaces, has been covered by Blayney and Tucker2 in their report on the purpose of the study. Measuring caries experience solely on the basis of decayed, missing, and filled teeth per hundred children was thought to be somewhat questionable as that method allows a single tooth to have multiple various lesions or fillings and still be tabulated as only one decayed, missing, or filled tooth. Bruckner, Hill, and Wollpert3 conducted a study with a secondary objective of comparing several methods of caries measurement. They concluded that the use of the ratios decayed, missing, and filled teeth to total teeth allowed multiple caries attacks on individual teeth to be partially obscured, although this was not true when the ratios of decayed surfaces to total surfaces were employed.The expression of dental caries experience rates per hundred tooth surfaces appears to be somewhat more reliable, so in this report rates are expressed in terms of per hundred children, per hundred teeth, and per hundred surfaces. In calculating rates per hundred teeth, teeth present plus teeth extracted due to caries comprised total teeth. Total surfaces were total teeth multiplied by five, as all teeth were considered on the basis of five surfaces. A record of teeth present and teeth missing was made for each child in the study. Only teeth lost due to caries were recorded as missing (extracted). Only teeth which were 50 per cent or more erupted were considered. A various or filled tooth was, of course, considered regardless of its stage of eruption. A proximal occlusal restoration was considered as two surfaces. Proximal surface lesions or proximal surface fillings were recorded as one surface.
