stuck- Gemara and S”A only say metitzah. To the best of my knowledged it never specifies by mouth. For all I know, doing it with a tube is just as good and is probably safer.
And it is a big machlokes whether Chazal knew science or not. I’m not saying one way or another, but there are Gedolim on both sides of the issue. If I’m not mistaken, the Gemara says we have to wash the baby with hot water after the bris because of sakanah (or something along those line) which we don’t practice anymore because it’s no longer a sakanah. Whatever you say either nishtaneh hateva or they were basing themselves on medical science that has been disproven, we don’t practice the science in the Gemara. Therefore, metzizah, which may have been done orally in the time of the Gemara, might be dangerous nowadays.