A stuck dental prosthetic is one of the odder origins of vampirism I've seen. I should use this book as the backstory of a game of Night's Black Agents : a vampire conspiracy of immortal sirens, deeply rooted in the Japanese entertainment industry, centered around a shadowy agency known only as 765. See how long it takes the players to realize they're playing Idolmaster.
(Presumably after consolidating their control over their own agency, they would go after 876, but it's a female-only infection, so Ryo has to pretend he's a vampire;. Then on to 346Pro and I really want to see Kirari as a vampire, nyowa. There could be cross-coven conflict with Chitose and Chiyo...)
To trace the vectors:
Yukiho -> Mami
Mami -> Ami, Yayoi
Ami -> Miki
Yayoi -> Haruka, Iori
Miki -> Chihaya
Takane -> Hibiki
Hibiki -> Makoto
Ritsuko -> Azusa
... So Ritsuko and Takane have unclear sires, and Yayoi is the most prolific tertiary vamp.