The demineralization of dentin grooves using an automatic pH-cycling system

Objective: The outbreak occurrence and progression of a caries lesion are associated with an imbalance of de- and remineralization. The pH values of the groove would be different in the situation of wide or narrow grooves. The aim of this study was to evaluate a demineralization of time-lapse analysis in a different width groove using an automatic pH cycling system. Methods: A 100 μm thickness single-section specimen was prepared from human extracted molar. All of surfaces of the specimen, except for the original surface, were coated with Sticky Wax. We made an artificial groove with 200 μm wide (N group) and 400 μm wide (W group) with 1mm deep in the specimen (n-6). The coated surface of specimen was covered with Para film. These specimens were immersed into a beaker with an outlet, resulting in spontaneous outflow of solutions. The demineralizing solution (pH: 4.5) was flowed into the plastic beaker for 2 minutes. Next, the remineralizing solution (pH: 7.0) was flowed into the plastic beaker for 60 minutes. A programmable electronic timer controlled 9 times cycle per day. The demineralization of dentin at the Enamel-Dentin junction (EDJ) and the bottom (BO) of the groove of the specimens under the both conditions was compared with mineral loss (ΔZ) at week 2 and week 4 on Transverse microradiography (TMR) images. Result: ΔZ (Vol% •µm) of the dentin at EDJ at week 2 and week 4 (779.2±89.7, 1195.3±199.4), and BO (857.7±152.7, 1557.8±206.6) of the W group were significantly higher than ΔZ at EDJ (159.4±70.6, 528.3±249.8), and BO (120.1±63.1, 364.5±99.1) of N group at each week (Paired t test, p<0.05). Conclusion: This result suggested that the demineralization of the dentin is depending on the width of grooves artificially made, being much more progressed in the wide than a narrow grooves.