3. Visit your insurer's website. Look for any policy statements related to your condition, and review the services your individual plan covers. Learn your rights and responsibilities for requesting coverage.

4. Engage someone at your health plan. It could be a nurse case manager or the medical director. And insist that the insurer follow its own rules. "Oftentimes, an insurer may have a legitimate reason for being concerned about a test or a treatment, but they have to follow a specific process" for denying a claim or pre-authorizing a service, Santa said. "Your request may or may not be covered, but the insurer has an obligation to provide due process."

5. Appeal. If you're not satisfied with your plan's response, don't be afraid to go through the appeals process. "The track record on appeals is favorable," Santa said. "There's a good chance you could win." In the case of autism, make sure your treatment plan is medically focused and targets deficits in social interaction, communication and repetitive or restrictive behaviors, said Kristin Jacobson, the president of Autism Deserves Equal Coverage, an advocacy group in Burlingame, Calif. "Health plans make it very hard for families," she said. "They count on families giving up. The ones who don't give up are the ones who eventually will prevail."

6. Beware of signing long-term contracts. Some TMJ patients have gotten locked into multiyear contracts with health care providers and continue having to pay long after they've stopped treatment, Cowley said. "In the event that the treatment doesn't work or you are worse, you are still obligated to pay that contract."

7. Maximize your benefits. If you have another medical condition that overlaps with the one you can't get coverage for, treat the one that is covered. Children with autism whose family health plans exclude that diagnosis, for instance, might find some relief by pursuing coverage for related conditions such as speech or motor-skills delays, Jacobson said. Your health plan also may have a separate disease-management program, for which you might qualify, that could help you with pain management or diabetes, should you need it.

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8. Consider hiring a private health care advocate. Choose someone who has handled many cases similar to yours. You can search for professional advocates near you at AdvoConnection.com and the database of the National Association of Healthcare Advocacy Consultants.