Using Cycles I was able to achieve the following result using the meshes from your
.blend. Not sure why your image has the funky artifacts, but as far as I can see the result I turned out seemed okay? I'll add the steps of how I achieved the result below... :)
1. To begin, after deleting all previous mesh data (Materials, UV Maps, etc- helped me to start afresh) and with the multires mesh selected, add a new 2048x2048px image in the UV Image editor. Then create a new Cycles material with this image attached to the diffuse colour (as this image needs to be applied to the multires mesh in order to bake the normals, and plugging it to the diffuse colour will help us view it in Textured View Mode later on if need be).
2. Next enter edit mode and UV Unwrap the multires teeth mesh onto the new image.
3. Now we can head over to the Render settings in the properties panel and jump to the
Bake tab. Change the
Bake Type: dropdown to 'Normal'.
4. You can change the
Margin to be '0px' and check the
Clear box beneath it. This'll just make the normal map look a bit cleaner, you can leave it at higher values if desired, it shouldn't affect the normal map. Finally, hit
And there ya go! You can save the UV Map externally by tabbing out of edit mode, hovering over the Normal Map in the UV Image editor and hitting F3. Hope this helps! :)