There's usually 16 teeth top and bottom making 32 in all.
You need lot of reference photos to really get the shape of each tooth because every one is slightly different you can get away with using the same ones at the back of the jaw but its well worth taking time getting the front ones looking right because you can always use them on other heads.
The teeth are finnished.
Now I'm going to start shaping the head a little more.
I've extrudeed some edges at the bottom making more of a neck.
Started adding a few details around the eye.
Making some wrinkles around the eyes.
Yet even more wrinkles...
Now looking from the side. Marked green I decided to change the flow of the lines down the cheek and chin area, marked in yellow are where the old lines use use to follow.
Added more detail around the eyes.
Here's how my wrinkles are looking so far.
Now I'm trying to get the shape of his older face and trying to get some skin hanging under his chin.
More 3D Graphics: 
