Surface Roughness Measurements of Enamel During De- and  Subsequent Re-mineralization

The surface roughness parameter R_a is a measure of the topography of a surface at the micron level.  Previous studies have demonstrated that the R_a of enamel increases following an artificial carious challenge, suggesting the surface does not demineralize uniformly, and acid attack increases the surface microporosity. This increase in surface energy may assist subsequent remineralization. The aim was to continuously measure changes in R_a as a function of time throughout demineralization, and, to further measure changes in R_a of the same enamel surfaces during subsequent remineralization.

Method:

R_a measurements were obtained using a Proscan2000 Optical Profilometer (Scantron Ltd, Taunton, UK).  Thirteen caries–free enamel surfaces were cut from teeth of unknown origin. Each sample (5mm square, 3mm thick) was attached to the profilometer using a kinematic mount to facilitate removal and subsequent relocation of samples.  Initial profilometer line scans (length 45mm,  step  1.0 µm) were obtained, then each sample was removed, exposed to caries simulating demineralizing solution (pH=4.0) for 12h,  and then relocated onto the profilometer for further measurement.  This cycle was repeated for 200h.  Subsequently, each sample was exposed to remineralizing solution containing 2.4mM Ca²⁺ (pH 7) and further profilometer scans taken after every 12h throughout remineralization for 800h. Control samples were exposed to deionized water only.  R_a was calculated and plotted as a function of demineralization time, and remineralization time.

Result:

Demineralization:  R_a increased linearly with time (total increase in R_a for each of the eight samples was ≈1.5 µm in 200h). Control samples showed no change in R_a.

Remineralization:  Initial rapid decrease in R_a during first 38h, then little further decrease for 400h, then substantial decrease returning to original values after further 400h.

Conclusion:  

Surface roughness of natural enamel surfaces increased linearly during caries-simulating demineralization. During remineralization, R_a  almost returned to original values, but after considerably longer duration.