Close Mysql Connection

[Muazam]

How do I close vbulletin's mysql connection?

I have custom pages that uses:
global $vbulletin;
require_once('global.php');

It seems to lagg my server after a while and crash it, I don't think mysql is getting correctly closed. I've read that it closes automatically, but is there I was I can ensure it's closure?

Thanks,
Muazam.