For each message you want to add to a multi-quote, click the "+Quote" at the bottom of that message. (When you do, "+Quote" will change to "-Quote." When you're ready to reply to the messages you're quoting, go to the message blank at the bottom of a page and click "Insert Quotes." A little window will open up that will let you choose which of your chosen quotes you want to reply to in your new message. You can place your cursor wherever you want within the message to reply to the quotes individually. (Gosh, I made that sound complicated---am I making any sense?)
[Hah! I was late to that party! Brad explained it all while I was still typing!]
I hope your tooth gets sorted out soon. Been there myself all too often ... a good, trustworthy dentist is worth his or her weight in gold.