Re: Accompany a friend who's suffering from dental phobia and is going to get her wisdom teeth remov
Bless you, pwypo. You sound like a great friend, both for helping your friend through her procedure, and for coming here to look for advice. I suspect you're already armed with the tools you need: empathy and compassion.
I don't think there's anything specific you can do that you wouldn't do for anyone going through any terrifying experience. Hold her hand, make it safe for her to cry and be vulnerable, assure her that she's safe and in good hands. I'd recommend reading through the "common fears" articles above, to get an idea of the types of things dental phobics worry about.
It's usually helpful to tell the staff that the patient is phobic, or at least very anxious and scared. Most dentists and their teams (including the front desk) are pretty familiar with how to deal with scared patients, and will make an extra effort to be comforting if they get a heads-up. Many phobics are embarrassed about our phobia, or worried that the staff will lose their patience with us because we can't act "normal"-- sometimes this results in us clamming up and acting brave, which adds additional pressure to maintain our composure. Remember to respect your friend's dignity at all times, even if she's coming a little undone. (e.g. "My friend is very uncomfortable about needles, can you take extra care with her?" vs. "Watch out, she's going to freak out when you give her the shot."
Be aware that most phobics feel like we're walking into a death chamber when we go to the dentist. Facts and statistics don't really help combat this feeling, although lots of "This is a very safe procedure" and "You're in really good hands" kind of reassurances in a calm voice help. Anything you can do to make your friend feel safe to let her scared little girl out (however old she actually is) will probably be helpful. Many people find comfort in bringing a teddy bear or blanky with them, once that permission is given. Being allowed to cry a little helps. Laughter helps. Distraction helps.
Sympathy ("oh, you poor thing") generally does not help. Denial and rejection ("it's no big deal, don't worry") don't help. It's a fine line sometimes between reassurance and rejection: the things we're afraid of are irrational, but the fear itself is very very real. In general it's better to meet the fears with general statements of comfort rather than trying to refute them with facts. "I'm afraid I'll never wake up from GA" is better met with "It's a very safe procedure, they'll be monitoring you very closely" than "98% of people experience no negative affects at all." (And certainly not, "That's crazy talk, nobody dies at the dentist!"

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I think you probably already know most of that instinctively. Mostly just remember that you're helping a good, rational, dignified person through a very vulnerable, terrifying, undignified time. The doctors and their team will take good care of her physically and emotionally through the procedure; your job is deliver her into their hands, and be there to receive her when they're done.
As a phobic who went through all this mostly on my own, I thank you for being a great friend to your friend.
Good luck to you both!