The following is just my opinion, in case anyone is interested. These are just rough measurements. Make the formulation your own, after the third time you make it, you'll know how you like it. Use all organic ingredients.
2 tablespoons of coconut oil
2 capsules (1 teaspoon) of activated charcoal powder
1 1-2 to 2 tablespoons or turmeric (or curcumen, however it's spelled) powder
1 teaspoon of cinnamon powder.
Take away a little oil or add a little more turmeric/charcoal to adjust thickness of paste. It will NOT have the consistency of commercial toothpaste. It will be more "liquidy" and you'll have to mix it every time just before using it. I also think it actually helps to leave it in your mouth for a minute or two after brushing so that the charcoal can keep doing its job.
Have fun with it!