Legally speaking you already own your healthcare data such as dental X-rays. In many cases you can even download your data from provider and payer organizations in industry standard formats (although dentistry specifically is way behind in this area). But for most patients this data is worth zero. Legal and privacy concerns aside, there's just not much use for it. Several start-ups have tried to de-identify and agregate such data for sale to researchers but consistency and quality issues make it tough to use in real studies.