The spacers only take a few minutes to apply. I had five put on, and it took about ten minutes. It would have been faster, but they had trouble getting one of them to "sit" properly. It took three people!
The orthodontist uses dental floss to hold and stretch the spacer, which is a small, rubber disc. It feels just like a rubber band. It's soft enough to be comfortable but firm enough to put pressure on your molars. They use the dental floss to "shimmy" the spacer down between your teeth and then pull the floss out of the spacer once it's seated.
Spacers are designed to create room between your molars so the orthodontist can put the bands on when it's time for your braces. The more crowded your teeth, the more pressure you'll feel, so this might be why I didn't have too much pain. The extractions left a lot of space in front of my molars, so they had lots of room to move.
I felt some pressure under my nose and in my cheeks the first couple of days, similar to a sinus headache, so I took some Tylenol. I read that ibuprofen/Advil can slow tooth movement, so I stopped taking it once the spacers went on. My teeth were still tender from the extractions, and now the spacers, so I stuck with soft food. I'm still eating soft food, but again, that's mostly because I'm still tender from the extractions. I'm not taking Tylenol anymore, so I think my mouth has gotten used to the spacers.
The spacers feel like I have something between my teeth (because I do), but it's not irritating. I can sort of feel them bouncing together, like chewing on a rubber band, but since I'm only eating soft food that I can kind of "mush" around my mouth, I don't get that sensation very often, so it's not bothering me.
I'm very gentle while brushing my teeth. You can't floss with spacers, or they'll come out, so I'm taking heed while brushing too. My orthodontist said to make an appointment right away if one comes out, as adult teeth will close right back up if left that way for a day or two. So, I'm being really, really careful. :)