I don't know any personally, but I don't see why it couldn't work. Really, it's up to you two to make a decision to do residency/set up a practice in the same place when the time comes. i.e. she could choose to restrict her residency applications to areas where it would be possible for you to set up a practice. Of course, this only makes sense if the two of you are pretty serious at that point and planning on spending your lives together. But it's definitely possible to make sure you both end up in the same place, if you want to. Some career sacrifices may be involved for one or both of you but they shouldn't be too serious; there are plenty of good residency programs in most major cities and it should be possible, I would think, to set up a dentistry practice pretty much anywhere you want. If the relationship is important enough to you, you'll make being in the same place a priority when the time comes. If the relationship isn't that important to you, you won't. Either way, if you want to be together, you can be. That's what it comes down to. You gotta make a decision that you want to be together and if you want to be, then you will be.
BTW, my husband--who was then my boyfriend--and I faced this decision with regard to medical school, where it is MUCH harder to coordinate that you end up in the same place than with residency/setting up a practice, where you have comparatively a lot of choice. We worked it by choosing only to apply to major metropolitan areas with at least three medical schools, and hoping we'd both get into schools in the same city. We were betting on NYC, since it has 6 med schools...it worked out for us and we both got into the same med school. If we hadn't both gotten into the same school, one of us probably would have put things off a year and reapplied, or we might have tried to transfer. It's all about commitment and making a decision that you want to be together, and then planning with that in mind...if we hadn't coordinated our med school application process so carefully, we probably wouldn't have ended up in the same place just by accident. You gotta make a decision that you want to be together, then do it. For us, being in the same city was a major priority and we planned with that in mind. Good luck!