I'm going to play Dr Phil for a moment. A lot of bullying profs and row instructors are out there because like someone else said before, they suck at their private practice. And of course, for the most part, most instructors are excellent clinicians who want to teach their skills. While I see a lot of sympathy posted here, let me give you some advice.
Whenever a prof puts you down, here's what you do:
1) Call them out on it:
Dr _____ are you having a bad day?
Dr _____ have I done something to upset you?
2) Tell them how it makes you feel:
Because the way you're talking to me isn't helping me.
Because what you just said embarrassed me in front of the patient.
3) Correct the situation:
I know I'm a student, and I'm not going to get a perfect the first few times, but I would appreciate it if you could be a little more constructive.
I realize now that I should have gone about this a different way, and I see that, that's why I'm here to learn, but I would appreciate it if you could be a little more constructive.
If I've done something really out of bounds, I'd appreciate it if you pulled me on the side and told me, because I don't want to lose my patient's trust.
Be humble and respectful. If that doesn't work, step up your game a notch:
Dr _____, it's obviously I'm not going to learn anything from you, so I think I'd better see a different row instructor (and if you pull this card, you have to back it up by seeing someone else).
Dr _____, I feel like I haven't communicated how I felt to you completely, so I think I'll talk to the dean/dean of students/etc (and walk out for dramatic effect).
Parting shots if you want to stick it to them:
1)Seriously Dr _____. Why are you here? Is it to help us or not?!?
2)If you're here to guarantee my failure, I'll tell you right now you're right on track!
3) So what you're trying to say is I should quit right now? Just quit?
4) *quote any humanistic teaching model that the school incorporates*
...ensuing responses may be comical.
Of course, it takes a certain amount of self assurance to pull of steps 1, 2 and 3, and then balls of steel to pull off stepping up your game, and then god-like powers to pull off the parting shots.
Use these at your own risk. Practice them if you have to. Edit/add/create your own phrases. Be confident, and don't break down. Be ready to think on your feet if they come up with a smart response. I went to a school with a stellar humanistic teaching philosophy, and we've only had one problem with one row instructor. Enough of us complained to the higher ups, and her attitude quickly shifted a week later.
Don't cry. Elevate yourself articulately, and by doing so, you'll pull them down and show them how much of an ass they're being. If you run away and sniffle, you'll be victimized your entire dental school career, and possibly by your future employers and partners.
Stand up for yourself. Push back if you have to. Yes you're dental students, but yes, you're human beings too.