For caries to develop in enamel, acids must be transported into and mineral building blocks transported out of the area of demineralization through the superficial intact enamel layer. Although the issue is extremely interesting from the standpoint of the physiological protection of erupting permanent teeth, researchers have examined the phenomenon of reduced permeability of the enamel of deciduous teeth before exfoliation only once and found that the permeability of deciduous-tooth enamel decreases during the process of root resorption. The few studies on living permanent animal teeth have shown that diffusion processes occur much faster in living teeth than in extracted teeth or teeth from which the dental pulp has been removed, but the results of these studies vary greatly or even contradict one another.

Using the electron paramagnetic resonance (EPR) method, we measured the permeability of human tooth enamel to a water-soluble spin label. We supported the method by measuring the amount of free water in enamel, which constitutes the medium for diffusion processes.

Enamel specimens were cut from single-rooted permanent and deciduous teeth and divided into four groups: (A) enamel specimens from deciduous teeth with roots resorbed by no more than half, (B) enamel specimens from deciduous teeth with completely resorbed roots, (C) enamel specimens from permanent teeth of younger patients, (D) enamel specimens from devitalized teeth, and (E) enamel specimens from permanent teeth of older patients. In all specimen groups, we determined the mean diffusion coefficients (D):

D(A) = 10,72 ± 2,83 × 10-7 cm2/s, D(B) = 3,22 ± 0,66 × 10-7 cm2/s, D(C) = 7,03 ± 0,61 × 10-7 cm2/s, D(D) = 5,75 ± 0,28 × 10-7 cm2/s, D(E) = 4,45 ± 0,37 × 10-7 cm²/s.

In the groups, we also determined the mean weight fractions of free water (W) by drying at room temperature for one hour:

W(A) = 6,03 ± 0,62 %, W(B) = 2,04 ± 0,16 %, W(C) = 4,02 ± 0,70 %, W(D) = 3,82 ± 0,67 %, W(E) = 3,16 ± 0,71 %.

Our results support the findings of the previous study that the permeability of the enamel of deciduous teeth with completely resorbed roots is lower than that of deciduous teeth with partially or non-resorbed roots. The observed reduced permeability of devitalized teeth, together with findings on the role of enamel permeability in the caries process, indicated the possibility that devitalized teeth are more resistant to caries than vital teeth. The results of the work support the assumptions about the important role of deciduous teeth in the physiological protection of erupting permanent teeth and the role of the pulp of permanent teeth in the development of caries.