Run a small diamond lap along the flat faces, as Reno says, don't touch the diameter. This is a technique I use to keep router bits sharp. Don't overdo it, a diamond lap will remove metal very quickly. Sharpen little and often, as a keen edge lasts longer than a blunt one. A badly blunted cutter may not be revivable. I'm not sure what the 'titanium' coating is supposed to do, apart from giving the marketing departments a bit of snake oil!
One supplier;
http://www.eze-lap.com/ 
