I don’t remember where, but I think I remember reading that some of the Soylent team and/or DIY’ers have taken to chewing gum.
It’s also important to note that a good deal of the people using soylent aren’t doing so exclusively – most people still eat some amount of “real” food, subbing in soylent for some percentage of their non-social or non-significant meals.
I’ll agree though that for those using soylent for a majority of meals, this is an important thing to at least keep in mind, to avoid possible jaw atrophy. Chewing gum sounds like a really good solution. As for the actual mixture having negative effects on teeth, I don’t really have any basis to judge that, but the linked thread looks like it has some good discussion