I started a new job a few weeks ago and yesturday my boss asked me, "why is it hard (for people) to clean behind the bottom front teeth? so that we (the dentist) spend most of our time cleaning there rather than any where else in the mouth?" the answers that I have come up with have all been WRONG! (as he says) and I have asked the other dental assisstant and my friend that was a dental assisstant for a few years and they both have said because it is a small compact area difficult for the bristles of a brush to be at the right angle to clean properly which then has to be scaled. But he says this is also wrong. And I have to have an answer tomorrow.

There is a saliva duct under the tongue. When plaque isn't removed thoroughly on a daily basis the minerals in the saliva cause this plaque to harden.

Well the current theory is complicated, has to do with pH (acidity) Basically the lower inside of the teeth is always filled with saliva so has a very high pH (low acidity) so calculus (tartar) can form easily there.