CAUTION: Oral B12 Methylcobalamin Can Erode Tooth Enamel? I was using high doses of liquid vitamin B12 in the methylcobalamin form orally, and after a week or so, found that the B12 had thinned the enamel on several teeth, near the gum line and also just under gum line. I suddenly felt felt a strong and quite horrible sensitivity every time my toothbrush touched the teeth in this area. At first I did not know what this tooth pain was, and I though it might be some new cavities. However, there were no signs of any cavities, and normally you do not suddenly get cavities in several teeth all at once, within a week. As I had only recently started experimenting with high doses of liquid vitamin B12 placed on my upper gums, I had a hunch that this B12 might have caused my tooth sensitivity, and sure enough, an online search found some anecdotal accounts of tooth enamel loss through B12 methylcobalamin oral/sublingual use (though I cannot find any proper scientific references to this phenomenon). I don't think this B12 tooth enamel erosion is of major concern for people here taking sublingual B12, and/or B12 on their upper gums in the excellent method described by Freddd. But is is something to be aware of, just in case you are getting increased sensitivity in your teeth and don't know why. I think the reason that my tooth enamel was eroded so fast was because I was using high doses of liquid B12 on my upper gums, and when I applied it, this liquid was actually running into the crevices between my teeth, and under the gum line, and remaining in these crevices for hours. I was applying these liquid B12 drops several time a day too, so this B12 was in constant contact with my teeth: ie, the enamel just under the gum line was almost constantly exposed to liquid B12 all day. The enamel just under the gum line is very thin anyway, so it is not entirely surprising that this portion of my teeth lost enamel and became sensitive. But there is a happy ending: I stopped all use of sublingual B12 for the moment, and got hold of some amorphous calcium phosphate tooth remineralization toothpaste (one of several types of tooth remineralization technologies), and in addition, I placed small pinches of bicarbonate of soda in my mouth a few time a day (since remineralization of teeth can only occur when the oral environment is not acidic). I also put some di-calcium phosphate powder in my mouth several times a day (tooth enamel is made from the hydroxyl ion combined with calcium phosphate, both of which are naturally found in saliva, as this is the way saliva works to constantly rebuild tooth enamel). After 5 days or so, the damaged teeth seemed to be better (the horrible sensitivity virtually disappeared), which I assume is due to the enamel being rebuilt by this remineralization process.