Imagine walking into an office, laying down onto your back, and someone covering your face with a thick green cloth with only one small slit. That slit is for your mouth. No one talks to you, except to say "Auflassen" (as in, "Keep your mouth open"). Then they spray your mouth with a strong smelling unidentified substance, and your gums, tongue, and lips go numb. Next comes the whizzing and whirring of various instruments that dive into and out of your mouth. Your lips are dry, but no closing your mouth, no rinsing until it's all over.
This was my first teeth cleaning in Germany, and it was as terrifying as you might imagine a German dentist to be. I should first clarify that I have never had a problem going to the dentist. Doesn't stress me out or make me uncomfortable, and I have had plenty of drilling down on my cavity-prone teeth. Now I am scarred for life.
When I was finally allowed to rinse there was obviously blood in my mouth. I floss - my gums don't normally bleed. They did not offer me a tissue to wipe off my face where water and toothpaste and whatever else had sprayed me (the slit moved a little - and there was stuff spraying everywhere). I really don't know exactly what they did, except clean my teeth German-style.