What conditions of enamel facilitate the post eruptive uptake of fluoride?

The uptake of fluoride post-eruption is facilitated by conditions that promote the absorption of fluoride ions into the enamel structure. Surface demineralisation makes enamel more porous, allowing fluoride to penetrate more easily. When the enamel surface is demineralised, it creates a more favorable environment for fluoride to bond with the enamel, leading to the formation of fluorapatite, which is more resistant to acids than hydroxyapatite.

Hypo mineralisation refers to enamel that hasn't fully mineralised, resulting in areas that are less structurally sound. Such areas can also absorb fluoride more readily compared to fully mineralised enamel. Therefore, both surface demineralisation and hypo mineralisation provide conditions that enhance fluoride's ability to integrate into the enamel.

In contrast, other conditions mentioned, like hyper mineralisation or normal enamel, do not promote enhanced fluoride uptake as effectively since the surface is denser and less permeable. Therefore, it is the combination of demineralised surfaces and hypo mineralised areas that optimally facilitate post-eruptive fluoride uptake.