Nanobots

Long ago, Sally would have had to clean her teeth with a brush, fluoridated goo, waxed string, and medicated rinse.
Now, it’s done with nanobots. Tiny robots programmed to scrub away food particles, eliminate bacteria, and rebuild any damaged surface material.
Everything is done with nanobots. Zapping cancer cells, replenishing muscle fibers, healing bone, and enhancing nerve signals.
They’re not supposed to go into the brain, but they do.
The tooth maintenance routine doesn’t quite work in the brain, neurons sheathed with shiny hard enamel.
Sally collapsed in the mall, staring blankly, with a perfect dead smile on her face.