Add a Bezier Circle (Add-->Curve-->Circle) and delete one of its vertex.
Select the whole curve and press Alt+C to open it up.
Shape the curve to make it look as a grinding wheel tooth. Use V button to change the handle type, so you may for example make the teeth sharper.
Add an Empty, then set the Array Modifier for a curve (with the settings pictured below). Set the Count amount as desired. Rotate an Empty to create a grinding wheel. Now changing the shape of a one tooth will affect every other one.
In Object Mode press Alt+C to convert your curve to a mesh.
If you need more teeth, increase the Count amount and scale the curve to make the teeth fit each other. Enable a First Last checkbox to merge the first and the last teeth.