There's no visible problem when X-rays or endoscopes are used, so it is usually diagnosed by taking a history from the patient and using a process of elimination to learn that it is not some other health problem.
The electromagnetic spectrum includes (from longest wavelength to shortest) radio waves, microwaves, infrared, red, orange, yellow, green, blue, indigo, violet, ultraviolet, x-rays, and gamma rays.
This walkthrough also specifically mentions some of the routine diagnostic procedures done in the office, including a 3-D digital x-ray machine that minimizes actual patient exposure to x-rays.
This type of policy normally covers emergency room visits and hospital stays, diagnostic tests and x-rays, surgery, and medications while traveling, but coverage would end when the trip ends.
The percentage of cost covered by a dental insurance plan varies from policy to policy, but the standard rate is 70-80 percent of preventative dental care (exams, cleanings, X-rays etc).