Lavémonos los Dientes

We went to the Planned Parenthood used book sale in Santa Barbara this weekend and came home with some interesting books. One of the things I found was an old LDS hymnal in Spanish titled Himnos de Sión. As I was looking through it, I came across a song titled "Lavémonos los Dientes." Here are the lyrics in Spanish:

Los Dientes no me lavaré, Un niño exclamó
Ya me lavé, ya me peiné, con eso me bastó.
Mas en su boca se oyó un grito de placer,
Y los microbios sin temor, salieron a comer.

Dijeron, llenos de placer: Aquí hay buen hogar
Entre sus dientes sin lavar, podremos festejar.
Oyó el niño de su plan y pronto se lavó,
A los microbios él mató, ni uno escapó.

It took a little bit of searching, but I found an old post on Times and Seasons that contains the lyrics to the original English version (titled "Tooth Bugs"), which I'm posting here so all the gringos out there don't have to be stuck reading my own translation.

I do not want to clean my teeth, a little boy once cried,
I’ve washed my face and combed my hair, That's quite enough, he sighed;
Some tooth bugs hiding in his mouth, Began to dance in glee;
At last we’ve found a home,” they cried, We do not have to flee!

This boy has such a nice warm mouth, We’ll linger here all night;
His teeth are filled with bits of food, We’ll eat with all our might!
The small boy heard their shout of glee, Get out of there, he cried;
He grabbed his brush and scrubbed and scrubbed ‘Till every tooth bug died.

Two questions: how did this song ever make into the hymn book? And why did they ever take it out?