One application I've seen for this is recording your brushing patterns for your review and to recommend ways to improve your process. This is pretty useful right now considering dental hygiene literacy is criminally undertaught and uncommon even among adults.
IoT is great, it's just that companies right now are abusing it and our lack of data protection laws to extract as much personal information as physically possible. The question shouldn't be "why is my toothbrush connected to a network", it should be "why does my toothbrush need to be connected to the Internet".
Actually this one feels pretty similar to watch_dogs. Wasn't this the plot to watch_dogs 2?