"he's surely a person first, and a dentist second"
Well yes, and no. You have met him at work and he is a dentist there, first.
If you are really attracted to him the only way you can get into a relationship with him is if this develops outside his work. If you don't know where he lives and there is no crossover between you except in his surgery, nothing will happen.
Your gentle little thank you note won't bear fruit. He would never risk 'misinterpreting it' by seeing it as a come on. Imagine if it were just a polite thank you and he responded by seeing it as a sexual overture. He would be screwed professionally.
The only other strategy open to you is to be blunt and open. Tell him to his face you are attracted to him and would like to see him socially, but that you accept that if he is interested you will have to find another dentist. You have no choice but to do this at his workplace, but if you are honest and open and make clear you understand the issues, he might respond positively.
I know the position with doctors and from what the dentists on this thread have said it sounds identical.
I fell in love with my daughter's GP a few years ago - head over heels. There were weird atmospheres - oscillating friendliness and coldness - at the surgery. After a couple of years of this, we both got dogs and started 'bumping into' each other dog-walking and he befriended me (naturally I was receptive). We are both married. He did an awful lot of trying to bump into me (pitching up when I was doing the school run etc) but if I ever said when I would be there, he wouldn't show. Long story but he suddenly changed and avoided me like the plague for 3 months, actually putting his dog in the car at lunchtime and driving it out of town.
I was gutted. Then suddenly he turned up again and was obviously trying to spend as much time with me as possible. Nothing was ever said. Then he told me his wife was pregnant with twins and I realised he'd come looking for me as soon as he knew their IVF had worked. Prior to that I had been expecting a quite different declaration from him.
Needless to say I cut him out of my life, took myself out of the practice, hid at home. He responded to this by semi-stalking me, walking his dog past my house daily for two and a half years, having never taken this route before. Within three months of my cutting him out, he had lost about two stone and looked haunted,, all the time as an expectant father of twins.
I have no doubt this man was in love with me, but his being a doctor, his professional responsibilities and status and the fact that I was so off-limits meant nothing could happen. Rather than leave it alone he fudged things. He was addicted, but tormented. It was all a mess and my marriage was profoundly damaged. I have no idea what his situation is like now, but it was a sorry-looking relationship to bring twins into. I am over him now, but it took a long, long time.
Sorry for the essay, but I have learned from this experience. These professional responsibilities are very serious and the boundaries have to be maintained. I think it's easy to forget sometimes how important men's jobs are to them. You and this man may both be single and this is of course very, very different, but any personal relationship would have to be completely separate from the dentist-patient relationship. Anything else would be unprofessional.
A postscript is that I am now three years into training to be a doctor myself and I understand much better than I did five years ago how strong the taboos are. Knowing what I know now, I would run a mile from the situation I got myself into, it had to end in tears. It is not just from a medico- (or dento-)legal point of view that all this matters, it is innate to the almost mystical trust that is deemed to be implicit in the relationship between the professional and the patient. Trust me, by the time training is completed, these values are (or should be) hard-wired. If you start this training at the tender age of 18 (not at 38, like me!) this is absolutely the case.
So when you say someone is a person first, and a dentist second, I say, well, yes, and no. One of the doctors I met first in my training, who had a big impact on me was a cardiologist who told me that she identified herself as a doctor even before she identified herself as a wife and mother. That being a doctor was almost part of her DNA.
Again, apologies for the essay. I sympathise a lot with your situation, but I don't see a relationship coming out of this unless you accept and understand the boundaries and how clear they have to be. I don't get the impression from your posts that you really do understand the issues or take them seriously and you really have to if you are serious about a relationship with this man. If you gain him as a lover, you will have to lose him as a dentist. It's not unfeasible that you gain him as a lover but not while he's your dentist, no way. Good luck OP. You will have to decide if you are prepared to blunt.
Btw, I am a tall woman as well, and I prefer tall men. I married someone my own height, but I've always wished he were taller. We are divorcing now. If there is ever a husband no. 2, he's going to be very tall indeed!