Most gear design software will have some way of exporting the tooth profile. The one I used has a dxf export option that allows you to save a single tooth or the whole gear profile. I then import into UG and extrude and subtract.
I did it before by drawing one tooth then I used circular pattern to array it on the whole body but you need first to calculate number of teeth and module.
I did it before by drawing one tooth then I used circular pattern to array it on the whole body but you need first to calculate number of teeth and module.