I have not tried DIY Soylent so I can’t comment on that, but I do have fairly severe teeth sensitivity and have been to a dentist so I can tell you the potential causes and solutions.
For me, it’s caused by eroding gums. This sounds much worse than it looks, basically the gums are just not covering the roots of my teeth as much as they used to. A dentist can tell just by looking. The cause of gum erosion is brushing too hard, according to my dentist. He told me to get an extra soft toothbrush and hold it like I would hold a pencil, to prevent me from pressing too hard. He cautioned me to never press hard when I brush, and said it’s the length of time that I brush that gets the plaque off, NOT the pressure I use on my teeth.
Complicating tooth sensitivity, in addition to gum erosion, is enamel erosion. My dentist told me I must use a toothpaste that contains fluoride to help with this.
So in conclusion, I have switched to an extra soft toothbrush, switched to a toohpaste that contains fluoride, and make sure to not press hard when I brush. Over the past year this has slowly but surely reduced my tooth sensitivity significantly.
Anecdotally, I have found that consuming products with aspartame cause my teeth to temporarily become more sensitive, until several days pass since the last time I ate aspartame. No idea on that one, and have never heard anyone else say it, but it’s happened to me 20+ times and never fails.