Hi SuperDuperDude, i had to reply to this because i had/have the same problem, although i overcoming very rapidly with the help of EFT (link at my sig), visit also
Tapping.com - Free EFT Videos - Emotional Freedom Technique for some free videos to get started quick, i looks ridiculous, but it really works, what it will do for you is that it will set yourself free of those limiting beliefs that make you feel anxious in social situations, it did wonders for me, and it will do that for you to if you get doing it, i strongly recommend it to you, it will change your life.
But i belive that is only half of the battle, you still need to learn a few things, the book that Shamou recommended is awesome, i recommend it to you too, also try searching for more info about social skills, or charisma, that will help you learn those skills that you havent learned from lack of practice.
You know, what you say about the dentist is pretty similar to something i had lived, i went to see my psycologist to thank her for the help she gave me for overcoming my school problems with study and socializing, and i went with my mother, when we arrived my psycologist started to talk to me and my mother replied for me, and my psycologist told my mother that she needed to let me do the talking... it doesnt matter the causes of why we arrive at beign social phobic, the important thing is that we can do something to overcome it.
Something called "affirmations" also helped me. Before i got into Affirmations i also changed my mind about feeling dumb, so instead of beign worried about looking dumb, i accepted it, i embraced it, so no matter what i did i allways assumed that i was allready making the ridicule of myself, this helped me to see my clumsyness in a very relaxed and worry-free way, and it had the effect that i started to see and also accept the imperfections and clumsyness and dumbness in others, wich made me feel more comfortable and confident. I also heard this way of thinking no so long ago in a TV show... weird...
I have come a long way with the help of EFT, thats the most powerfull thing i encountered, but even if i have still a little of fear left, i am still pretty stupid in social situations, for example just a few minutes ago i had to open the door to the girl who cleans my house, and she said "oh the climate is so hot!" (something like that) and since im so retarded

the only thing that went through my mind was "yeah?"... and then awkard silence... the good thing is that i dont worry about this anymore, i find it funny now, but it also means i have to learn some skills, because all this years of not socializing made me stay at the conversational level of a 5 year old

, but i can overcome, i have no doubts.
Good luck, dont forget to try EFT, it will change your life.