★★★★★
I used the known Japanese toothpaste Apag... for a few months and this black area reminerilized and turned white. Only a small part deeply in the root remains still black where the toothbrush is hard to reach. I have also tried another hydroxyapatite toothpaste without success. The Japanese one has nano-HAP. I used it in combination with a truly ultrasonic electric toothbrush (Megaso....) and this may helped sending the nano- HAP even deeper in the tooth enamel.
Japan has a history using nano-HAP instead of Fluride, to reminerilize teeth.
A photo before using nano-HAP.
https://ibb.co/CvMKkB5
If I find time I will post an after photo of my tooth.
