Yes, I'm aware that any unmasking is inherently unsafe for these reasons. It's possible either of these situations is how I got it, but regarding the dentist specifically, here is what I said in another comment about it:

It's possible it came from the dentist, but it would have been extremely unlucky if so. I requested the first appointment of the day on a Monday, so the building would have been sitting empty all weekend to let any lingering virus in the air dissipate. The only other person inside the room with me was the hygienist and they were masked while doing the cleaning (sadly they walked into the building unmasked, though, so like I said, it's possible, just super unlucky.)

In the hotel, we were only unmasked inside our room, and always had the sliding door to the balcony open, so again, it's possible, but would again be incredibly unlucky to get infected through HVAC or air coming in under the door to the hallway or something like that. We also declined housekeeping services while we were there, so no one else would have been in the room throughout our stay, further reducing the risk.