Plaque and saliva samples were obtained from 55 children aged 13–15 years: 23 of them were caries free (group N) while the other 32 had evidence of high-caries activity over the preceding 2 years, with a mean DMFS of 25.9 (group H). The average concentration of calcium in posterior plaque of children in group N was 3.57 μg/mg (dry weight), compared with 1.63 μg/mg for group H. The average concentration of calcium in anterior plaque was 11.55 μg/mg in group N and 2.57 μg/mg in group H. The differences between groups N and H were statistically significant (p < 0.01). Similar significant differences were found between phosphorus levels in plaque. Although the mean levels of both calcium and phosphorus in saliva were higher for group N than for group H, only for phosphorus did the difference reach statistical significance (p < 0.05). The present study therefore shows that levels of both calcium and phosphorus are significantly higher in plaque taken from children with no caries experience than they are in plaque from children who are caries suscep
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