Line-by-Line / Technical Critique
Containment procedures are intriguing.
SCP-5150-1's anomalous attributes manifest once it is in possession of human teeth. Once this task is complete, SCP-5150-1 will insert these teeth into its mouth.
That's… an anomalous effect? Just, putting teeth in its mouth? Is that actually anomalous?
For an inexperienced D-Class, he seems to accept the fate of this appointment pretty quick after getting his teeth torn out. Like, wow. No more resistance? What a baller. And I mean that in, "I really doubt anyone would act that way".
It has been assumed that this was a byproduct of it's exposure to sugar.
This line is unnecessary and interrupts flow. I say cut it.
The use of nitrous oxide was not reported, however, plausible in this circumstance as the subject remained conscious throughout the operation.
This is missing some words and should be two sentences. I would make the comma after "however" into a semicolon, and say "it is plausible", not just "plausible".
Big Picture / Conceptual Critique
Finished, this is an upvote though not a strong one. I think your description spoils too much of what happens — it could be confined to "SCP-5150 is a dentist's office that contains several anomalous entities that conspire to perform dental procedures on subjects that enter the building, typically with the result of the subject developing hyperdontia". Not as short as I just wrote it, but that should be about the amount of information you get across. Then your log can take readers by a lot more of a surprise. Also, I feel like the candy bar thing is fun but not implemented in a fluid way. It might have been better for the candy bar to have been a "flub" — unplanned thing that just happened to show up in this D-Class's exploration of the building. Maybe he had it on him… somehow. Or, it was a lollipop from the front desk — know how doctor's offices give kids lollipops? I dunno, something like that.
But it was a good little creepy thing, and that's about all it had to be, so +1.