Where can a veteran with disability rating of less than 100% go for free and/or affordable dental care?

Assuming you can't get discounted dental though your employer and you didn't retire from the military (otherwise you could get discounted dental through FedVIP), then on option would be though the VA's Dental Insurance Program (VADIP)*.

SGT Charlie Lee brings up a great point - many times if you have a teaching program nearby you might be able to get discounted/free dental procedures from them. This also applies with groups around you that may help out veterans - you're going to have to search for them yourself as there might be a group in NC that helps out Vets, but if you're in PA (for example), there might not be.

Humana and others have discounted dental plans for veterans .. but as with all dental insurance, you'll have to dig into the details of the plan to see what's best for your ... one may cover the dentist you go to, but only pay for 50% of the procedures; another may pay 100% of preventative procedures, but would have a limited number of dentists it might apply to; etc.

If you're facing financial hardship, there are a number of dental programs for veterans out there (EveryoneForVeterans, etc), but I assume that's not your situation.
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* VADIP - https://www.va.gov/health-care/about-va-health-benefits/dental-care/dental-insurance/