The use of teeth should be avoided if possible. They simply cut down the amount of linear overflow distance, which in turn reduces surface skimming. The only purpose teeth serve are to keep FISH out of the overflow.
The dimensions of the teeth are not really important. If they are to keep fish out, then they must be narror enough to do just that. The space in between the teeth (the solid areas) should be as small as possible while still allowing enough strength or rigidity not to break off if bumped.
As for the depth? make them as deep as you want. Lets put it this way.
Lets assume you have a 6 inch wide flat overflow and the water is 1/2 deep flowing over it.
Cutting 1/8" wide teeth 1/8" apart would basicly reduce the "linear overflow" area by half. This in turn would just about double the depth of the water going over the open area (so about 1")
Like I said, if the water going over the "flat" overflow is not enough to carry YOUR fish over, then don't use teeth at all. If you must use teeth, the more open area the better. Because wide gaps defeat the purpose, you need to make lots of small gaps very close together.
You will find htat most of the DIY and MANUFACTURED overflows or baffles that have teeth are nothing more than useless eye candy. People want them, so manufacturers put them in. They serve no purpose but an item without them may not "look" as desirable.
