And Nothing Happens
Every great journey of one thousand miles begins with a single brush. Wait, no that's not right. Every great teeth brushing experience of a thousand cavity preventions begins with a single step. Darn that is not right either. Oh well. I'm the narrator, and ipso facto I can do what ever I want. Today I want to regale you with a tale of teeth and toothpaste and Twilight Sparkle and alicorn magic which in this case is functionally equivalent to regular unicorn magic. Today I wish to regal you with the tale of Twilight Sparkle brushing her teeth.
Our tale begins, as these sorts of tales are wont to do, at night. Twilight had earlier in the evening consumed the last of her caloric intake of the day, yet held off on the act of brushing her teeth, because she wasn't sure if she would eat dessert or maybe a Taco Bell© Fourth Meal or something. After all, she often stayed up late into the night studying, researching, and generally being a perfect pony princess for little girls to aspire to follow in this brave new world in which we encourage little girls to pursue careers in STEM (Science, Technology, Engineering, Math) rather than be stay-at-home moms, or Celestia-forbid, liberal arts majors. Inasmuch, it is wise to condition them to view staying up into the wee hours of the night doing post-grad work while subsisting on coffee (or perhaps boba tea if they go to UCLA) to be a thing that is indeed normal as opposed to something actually useful, like sleep. However, on this day, Twilight actually did not indulge in any further food or drink, as she ended up getting ready for bed around 1:30 AM, which, TBH, was pretty early for her. That this was on the early side of bedtime for her makes clear that pehaps Celestia wasn't so wrong when she nearly elected to make Twilight Sparkle the princess of 
ed-up sleep schedules. Fortunately Luna and Cadance were there to remind her that Hasbro would have a fit, and she elected to instead promote her into something more capable of selling toys.
At any rate, having decided that finding an optimal solution to the three-body cuddling problem would have to wait until morning, Twilight Sparkle let out an involuntary yawn and deposited her papers into neatly-labeled folders and her books into neatly-shelved, well, bookshelves. After all, if she didn't have organization, what did Twilight have? A shutter ran through her body as she deigned to consider such a thing as an unorganized Twilight, and how such an abomination, were it capable of even existing, surely would, in the words of Goatfried Leibnibbles, be a product of the "worst of all possible worlds". Twilight shook her head furiously and consigned the very thought of such a Twilight to the purgatorial part of her brain that housed such abominable memories that she had naught but the option of sealing it up with several forget-me-so spells, such as that time she didn't get the extra-credit problem correct on her metaphysics test, that time she walked in on her BBBFF and the Cadance-formerly-known-as-foalsitter tickling each other, and most of all that one time Celestia wasn't perfect (for of all things Twilight Sparkle's world view swam around, rotated around, spun around, nay, revolved around, none were more central than the central tenet of centrality that Her Royal Highness Celestia was immaculate, ineffable, and ultimately, devine. Celestia had at first gently tried to prod Twilight away from this hero worship, but when her methods proved to be a bit too successful and her student began showing signs of instead worshiping Gerard Neigh and a cursory scan of her library checkout history revealed a litany of books and pamphlets with such malodorous titles as "So Your Heros Have Failed You: How to Start an Emo Band", "Goddess is Dead: The Complete Unabridged Works of Fried Rice Neighzsche", and--perhaps most worryingly--"Filly Scout Knots For Dummies", Celestia about-coursed and decided that there were worse things to be worshipped than herself.)
Rather than ruminate on such Lovecraftian horrors, Twilight instead elected to to trot up the stairs. As she ascended each step, rising to higher and higher heights, she pondered her own metaphorical journey, from a helpless foal to a student to a scholar to a princess. How queer that of all the unicorns (and flippyflappers and mud ponies) of the world, fate had decreed that she alone was worth of Alicornication. It almost made her want to write angsty real pony fiction in which she, an immortal alicorn mourning the death of her friends, sought a taboo relationship with her former mentor. Almost. She shrugged the thought off, unaware as she was that such dreary ideas were merely seeping in from her Select Equestrian Accepteds phase mentioned earlier. She proudly limited her RPFs to A.K. Yearling/Rainbow Dash slash. And even that only came about when she was really drunk. And no pony would ever read it. Ever.
Twilight Sparkle eventually made it to the top of the stairs. Stairs carved into the body of a great oak tree which was somehow still living despite inexplicably having its insides hollowed out into a library inexplicably containing living quarters because honestly who would ever live in a library oh right Twilight Sparkle would because she's a huge NERD. But seriously, it's almost like that library was custom grown/carved/whatever for her almost as if somepony was a chessmaster plotting out the course of the world hundreds of years in advance. Not that anypony would ever do that. Ha you thought that was going to be a link to Celestia, didn't you? YOU WERE WRONG!
Just like Twilight Sparkle was wrong about her ability to use the restroom for her tooth-cleaning ritual, for lo and behold, Spike was taking one of his legendary seven hour bubble baths. Fortunately for the other resident of the household, Pinkie Pie had hidden toothbrushes with toothpaste already on them (like those ones at the Minuette's dentistry office you use right before getting 5 fillings because you don't floss enough and because you don't floss enough the cavities are the ones on the sides of the teeth that are harder to fix and maybe you shouldn't spend so much time hanging around Sugar Cube Corner trying to score a date with Pinkie Pie because seriously, everything they sell there other than the coffee and boba tea (which still is bad in the sort of excessive amounts Twilight Sparkle consumes it in) is bad for your overall health and especially the health of your teeth.) all over Ponyville "in case of toothbrush emergency" so Twilight Sparkle trotted back down the stairs, pulled a toothbrush out from under her kitchen sink, and brushed her teeth.