YOU SAID:

The only time I saw a banana was when there was a monkey is my tooth

INTO JAPANESE

バナナを見たのは猿がいた時だけ歯だった

BACK INTO ENGLISH

I saw bananas only when there was a monkey on my teeth

INTO JAPANESE

バナナは歯に猿がいるときだけ見ました

BACK INTO ENGLISH

I saw bananas only when there was a monkey on my teeth