Why is it that we brush our teeth like a madman right before our dental appointm!

Why is it that we brush our teeth like a madman right before our dental appointments?

I know alot of people out there do this. It's like we think all our neglect, and tarter, and cavities will brush themselves away. At least, one hour before our regularly scheduled appointment. I had an appointment at 8:30 this morning and brushed my teeth for almost 30 mins. Did I accomplish anything?
By the way, my appointment went fine. Just a cleaning and consult. Fillings and root canals come later. My next appointment is July 23rd.

Well, I think it's because people don't want the dentist to think we never brush. So they think the extra, thorough, last-minute brushing will get off tons and tons of plaque and tartar. It's our way of covering up our embarassment of not brushing as often as we should.

I don't think it accomplishes anything because plaque hardens over time, the only thing it does is get the soft plaque and gunk off your teeth that is more recent. Brushing has to be consistent to prevent the plaque from hardening. That is why we go to the dentist for cleanings, our toothbrushes alone--no matter how hard or long we scrub-- cannot remove the hardened plaque. So they use those lovely metal tools to scrape them off.. which I hate! But it's for the best :)