Data obtained in a longitudinal study of caries incidence and caries-r
elated factors were analysed with a view to producing a model for the
prediction of caries. In direct correlations, caries incidence was sig
nificantly associated with bacterial, dietary and salivary variables;
but when the data were examined by stepwise regression the strongest v
ariables were the baseline caries score and misuse of sugar. Counts of
Streptococcus mutans entered into the analysis but only as a relative
ly minor component. Similar significant relationships were seen with t
he determination of odds ratios. A caries activity test was formulated
combining the following caries-associated variables: high counts of S
. mutans, or lactobacilli, or the misuse of sugar, or frequent consump
tion of paediatric medicines. Regular use of fluoride tablets could co
mpensate for paediatric medicine use or misuse of sugar. Such a caries
activity test if it had been applied to the children at baseline woul
d have had a positive predictive value of 0.76, a negative predictive
value of 0.82, a sensitivity of 0.8 and a specificity of 0.78. Combini
ng tests made the prediction of caries more accurate and in the popula
tion for which it was intended gave a reliable means of detecting thos
e children most in need of enhanced caries prevention.