How many circuit layers in a MB?

I was wondering how many layers does a typical motherboard have? I recently scratched a couple of traces and one of them is deeper then I would like to see. I can not see any layering in the small gouge under the magnifier, but I am curious about how many there might be. I repaired the 2 broken traces with a PCB repair pen and the meter shows everything 'I can see' to be in functioning order. I am very tempted to trash the whole thing though and just order a new one so I don't take the chance of frying anything when I power up...

Advice, comments, suggestions... All are welcome.

Well I went ahead and pulled the trigger and fired the system up. It seems everything is a.o.k. right now... Screaming along very merrily right now actually. No smoke, fire, or burnt smelling foul! See how long it lasts ;)