There are good dental plans available on Healthcare.gov, but they are not necessarily the best available and you can only sign up for them if you are enrolling in a healthcare plan during a valid enrollment period. It is also important to remember that, unlike the healthcare plans which can be generously subsidized by the government, the dental plans are unsubsidized.
Ameritas has very good plans with a robust network.
Here are dental plans that you can enroll in OUTSIDE of the healthcare.gov market place. The first link is primarily for dental insurance. Many of the same companies that list plans on Healthcare.gov are listed here, but not necessarily the same plans for the same prices. Some of these plans also include vision.
The second link is for dental discount plans, which can be a better deal for some people.Unlike dental insurance, the discount plans never make any payments on your behalf. Rather, they simply negotiate prices with the dentist that contract with the plans. These prices are often less than half of what you would otherwise pay. These plans are typically paid for on a yearly basis, with the pricetag being around $100-130.
Often they are effective almost immediately, whereas dental insurance may have substantial waiting periods for most services. For people needing major treatment immediately, the discount plans are probably the best bet.