Combine all ingredients in a small bowl and stir together with a plastic or wooden spoon (metal is said to deactivate the clay, and while I’m not sure if that’s actually true, it's better to be safe than sorry).
Spoon the powder into a glass mason jar and screw on the lid.
To use, sprinkle a little on a wet tooth brush and brush your teeth like normal.
Notes
Store tooth powder in a cool dry place and use within 1-2 months.