I suspect there are few who actually hear from God and get "the calling" to become a dentist. I think an intelligence response to "why dentistry and not XXX" is to emphasize the exposure factor. I was exposed to and became interested in dentistry when this and that happened. I followed up on that intererst by doing this and that which enhanced my interest in the profession. As far as becomming an XXXX, that may have been a viable option for me, but I guess that I was never exposed to it to the extent that I became interested in persuing it as a profession.