Yes, it's called orifice flow (weir flow would apply for an overflow with no teeth). When I was designing my last overflow box, I developed a spreadsheet using the orifice formula to determine how high up the slots the water line would be at different flow rates. If you PM/email your email addy I can send it to you...
RC is down at the moment so I can't double check, but last time I looked there, their overflow calculator was for weir flow. Not really applicable to an overflow box with teeth...