Jeez, if you just had dental surgery, no wonder you're not very hungry.

especially if you're still on painkiller meds.
About the starvation mode theory...I've written my thoughts on that before. I think 'starvation mode' is talked about more than it actually occurs. Using WLS patients as an example - for 6-12 months following surgery, they are limited to less than 1000 calories a day for the most part, and told to exercise at least 5 times a week (from what I've read). If the 'starvation mode' theory was correct, these WLS patients would stop losing weight within a short period of time. (I'm not mandating going on a very low calorie diet - most WLS patients are medically monitored on a regular basis - there are very dangerous reprecussions to doing a VLCD on your own - any 'starvation mode' you might theoretically throw yourself into is the least of it, IMO).
Let's face it - in life there are going to be days that you will eat FEWER calories than you feel you 'should' as well as MORE calories than you planned. To me, the 'calories per day' should be used as a guideline - averaging out over a period of a few days or a week or two, KWIM? When I was recovering from surgery, I doubt if I ate 500 calories for the first few days (of course I was on several different painkillers and antibiotics...

).
I don't think it's a good idea to force yourself to eat if you're truly not hungry. As far as protein shakes go - it's really a crap shoot. What one person says tastes great, another person will think tastes like ca-ca. I haven't been to a GNC store in ages, but they used to sell individual packets of protein powders - that way you could try different ones before you settle on a favorite. (I used to do shakes once or twice a day pretty regularly, until I burned out on them...I prefer 'real' food these days.)
Have you asked your dentist about what you can and can't eat? he or she must have some recommendations. Maybe try soft-boiled or scrambled egg? oatmeal? or mix together light yogurt and cottage cheese (sounds icky, but it's actually quite good...).
I agree about the fruit juices. They're basically sugar water - eating the actual fruit is much healthier, with less calories and far more satisfying!