I know someone who did this. I think his reasons were similar to yours - he got a job as a dental assistant in undergrad and then went on to study dentistry. But towards the end of his dentistry degree, he had the opportunity to shadow a few doctors and enjoyed the experience so much, he went back to school to get his DO after completing his dentistry degree and after two years of practice. In fact, he practiced as a dentist part time for the first two years of DO school! (Although this was in the late 80s, don't know how feasible it would be to do that now).
I think the bigger thing you have to consider is since you were foreign trained, you will definitely need to have at least US prereqs for medical school before you can apply which can take a year or two. At that point of time, you should take the opportunity to complete clinical volunteering and shadowing doctors so that you can round out your application as a medical school applicant. I think being a dentist who was pulled to a career in medicine can be your unique story, and as long as it is compelling and justifiable (ie, you have shadowed doctors, you put in clinical hours with patients and know what you are getting into and what you want to leave behind), you should not have any problem just because you switched tracks.
All the best to you!