The most popular serration design is probably the Spyderco type and to maintain it to its original shape you have to have a tool that Spyderco no longer makes, which is pretty stupid. .....Spyderco used to make a set of ceramic sticks that had the exact contour of the Spyderco serration on one side of them and you can draw the serrated section straight down that side of the ceramic and they look better than new.
So why doesn't Spyderco make them anymore? Seems a bit silly, being as they sell a whole lot of serrated edges, all in the same grind profile.