Okay, I will admit it; I carry around a bit of cultural baggage. Although I've lived in places with differing expectations about time, I returned to North America with those from my youth intact. There is honestly very little that
bothers me more than missing an appointment. I organize my entire existence so I'm not late for anything. An appointment is an agreement between parties. I fulfill my end of the bargain by arriving a few minutes early and I expect to find someone else who's ready. I can be a bit anal about all this.
Although, I pride myself on my easy-going attitude, I don't have much patience when it comes to having to wait.
In fact, I will be looking for a new dentist now. Let me tell you why.

Yesterday, I rushed home from work. I found myself with very little time but managed to jump into the shower, throw on a clean shirt and make it to my dental appointment with about two minutes to spare. I was just going in for basic hygiene. I was welcomed immediately but then ushered to an empty room. I sat in the chair staring at the ceiling TV for much too long. Still nobody came.
As soon as my cell phone showed that I'd been there 30 minutes, I got up and went to receptionist. "It's rude to keep me waiting after I rushed to make sure to be here on time and this isn't the first time it has happened." I continued by saying, "I understand how a schedule can slip but this proves to me you have a scheduling problem. I do not wish to re-schedule this appointment and will not be doing so in the future." I left.
I get dental coverage from work and this means we are worth a great deal to the practice. Still, to me, customer happiness is paramount and there is no monopoly on dental services. Consequently, I'll be moving elsewhere.