What does this line mean?

[samfat33]

What does the poet mean by " Because the dentist may be a bear, or as the Romans used to say, only they were referring to a feminine bear when they said it, an ursa,".Its from "This is going to hurt just a little bit" by Ogden Nash.

[samfat33]

Please do post the meaning of this line in the poem.

[Anglika]

You have your answer on your other post. It's best not to post the same question in different places.