What about complications from using iron compounds and vinegar? As these might induce staining and erosion, which leads to sensitivity.
In first place, how Ohaguru even got trendy!!! Difficult to believe that people would paint their teeth black.
We’ve been living in a world where the fairness is treated as beauty and bright teeth are often regarded as clean . But the history itself is the reason for the present and future. I don’t have a problem if my teeth is dark or white , it should be healthy 