The other day, I was reading some Silver Age comics (natch) and I came across this plot point in Lois Lane No.50, from July 1964.
At first I was going to merely point this out and mention that from my experience with people of the generation that Lois would have been sliding through at the time, she almost certainly didn't get any sort of replacement; that right up until the original Crisis Lois Lane was missing a molar. How very strange by today's standards! How uncomfortable that would make some people feel!
And then the next day I heard about the Great Upcoming DC Reboot and the surrounding kerfuffle and the two got a bit muddled together in my head, such that when I got distracted by the new puppy and such I kept mulling it over and turning it around, and I came to this conclusion: Lois Lane's missing tooth means that reboots don't matter.
Think about it: by the strict rules of the ContinuiNerd, that tooth was gone up until the Crisis, but realistically it was probably forgotten by the end of the issue. The extraction, after all, existed solely as a means for Lois to learn about laughing gas (so that when she went back in time later on she could use some to try to disrupt Superboy and Lana Lang's first kiss - SILVER AGE!). But it happened, right? Theoretically, it should occupy as valid a space in the canon as Brave and the Bold No. 54, which came out the same month and featured the first teamup of Robin, Aqualad and Kid Flash in what would become the Teen Titans.
The obvious difference, of course, is that the tooth doesn't matter and that its absence isn't really interesting, whereas the concept of teen sidekicks getting together to fight crime does. If Lois had had her tooth replaced by a cunning fake that contained a Superman signal device or a piece of emergency kryptonite or something then it might have cropped up a few more times during the Silver Age, and had an appearance in All-Star Superman, and maybe Flashpoint Lois would have a secret spy tooth that shoots lasers or contains an emergency raft or has the Atom hiding inside.
Over time (and given good writing, of course), the fun, interesting, compelling stuff will keep coming back, while the drek and garbage and redundancies will fade away or be changed for the better: Krypto the Superdog will always come back, but Comet the Superhorse never will. Jimmy Olsen will never die but if we ever see the Blood Pack again it will be because someone has made something interesting of them.
Lois Lane is missing a tooth; Lois Lane is not missing a tooth.
It doesn't matter if Lois Lane is missing a tooth. Unless it makes for a good story, of course.