Influence of Storage and Flattening on Enamel De- and Remineralization

Objectives: The influence of various storage solutions on in vitro de- and remineralization of human enamel was investigated. Moreover, the effect of surface grinding (usually performed to optimize microradiographic analysis) was evaluated. Methods: 360 freshly- extracted human teeth were stored randomly in one out of four different solutions [formalin 10%; H₂O₂ 3%; thymol 0.1%; NaCl 0.9% (control)] at room temperature. After three months, a cylindrical enamel block was obtained from each tooth. The specimens were embedded in epoxy resin, ground flat (mean 176.2 µm, SD 101.3 µm) and partly covered with nail varnish. After demineralization in Buskes` solution (pH 5; 15 d), parts of the demineralized area were also covered with nail varnish; subsequently, the specimens were exposed to a remineralizing solution (35 d). Lesion depth (LD [µm]) and mineral loss (ΔZ [Vol% x µm]) were evaluated from microradiographs of thin sections (110 µm). The General Linear Model was used for statistical analysis, thereby controlling the effects of grinding. Results: Compared with the controls [demineralization: LD: 108.96 (SD 27.6); ΔZ: 4675.89 (1484.8); remineralization: ΔLD: 18.14 (19.4); ΔΔZ: 3316.47 (1271.2)], only enamel stored in H₂O₂ [LD: 74.16 (25.9); ΔZ: 2820.6 (1375.2); ΔLD: 11.50 (14.3); ΔΔZ: 1928.12 (1148.6)] differed significantly with regard to both demineralization (LD: p = 0.000; ΔZ: p = 0.000) and remineralization (ΔLD: p > 0.05; ΔΔZ: p = 0.000). Furthermore, grinding enhanced slightly (but significantly) LD and mineral loss in both the demineralized (LD: 0.080 µm/µm of ground surface (gs), p = 0.000; ΔZ: 6.18 Vol% x µm/µm gs, p = 0.000) and remineralized areas (ΔLD: 0.037 µm/µm gs, p = 0.001; ΔΔZ: 4.89 Vol% x µm/µm gs, p = 0.000). Conclusion: H₂O₂ does not seem to be suitable for storing human enamel. Flattening of specimens seems to have a small impact on de- and remineralization.