Outward fluid flow reduces inward diffusion of bacterial lipopolysaccharide across intact and demineralised dentine.

Objective: To examine the ability of outward fluid flow (OF) on resisting the inward diffusion of bacterial lipopolysaccharide (LPS) across the demineralised dentine (DD) in comparison with that across the intact dentine (ID).

Design: Twenty ID discs were prepared from freshly extracted human third molars. After etching both dentine surfaces, hydraulic conductance (L(p)) of the dentine was measured. Ten dentine discs were then completely demineralised using 10% EDTA, and L(p) was re-measured. The diffusion of LPS through ID and DD was measured against the OF and compared to the non-outward flow (NF) (n = 5 for each group) at 0, 1, 4 and 8h. Longitudinal sections of ID and DD surfaces were observed under a scanning electron microscope (SEM).

Results: The L(p) of DD was significantly higher than that of ID (independent t-test, p < 0.001). The application of OF and demineralisation significantly affected LPS diffusion (two-way ANOVA, p < 0.05). In addition, the effect of OF depended on dentine demineralisation. SEM images of ID showed intact dentinal tubules, whereas those of DD showed expanded collagen fibres and enlarged dentinal tubules.

Conclusions: The inward diffusion of LPS across DD differed from that of ID and the OF affected the inward diffusion of LPS. In the presence of the OF, the inward diffusion of LPS was reduced to near zero in both ID and DD. Nevertheless, when compared to that in the ID group, the OF produced the slightly greater effect to resist the inward LPS diffusion in the DD group.