My advice is to stop posting versions of the same question here and retain your own lawyer.
Avvo doesn't pay us for these responses, and I'm not your lawyer just because I answer this question or respond to any follow-up comments. If you want to hire me, please contact me. Otherwise, please don't expect a further response. We need an actual written agreement to form an attorney-client relationship. I'm only licensed in CA and you shouldn't rely on this answer, since each state has different laws, each situation is fact specific, and it's impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue.
One issue that will come up is whether your site crosses the boundary from providing information about orthodontist procedures to giving advice about orthodontic procedures. I strongly advise you to discuss your site with an attorney before you put it up, and consider a procedure to vet content.
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Create a corporation to protect yourself from personal liability. I do not understand your question about the domain name itself. And finally, I would highly recommend that you stop posting the details of your business idea, as I could turn around right now, retain a web designer's services and start this exact business. I would highly suggest you delete these posts. Good luck!
Your best and easiest step to reduce legal liability would be to contact a good business attorney - there are so many potential pitfalls here that you really need to be very careful. If this is anything more than a hobby, you should approach it as a business and spend the money to get good advice tailored to your specific situation, including from an accountant. E.g., will you have to register to do business in Texas and pay taxes there? Do you want to subject yourself to the jurisdiction of Texas courts? A reminder - corporate form helps protect you against contract liability- but if you personally commit a tortious act, you're still likely to be on the hook (think "insurance"). Good luck!