I recommend that you don't get it; I have not had dental insurance in probably at least 5-10 years.
When you go without, it creates an incentive system to encourage you to brush and floss every night. See if you slack off, you get cavities and its like a punch in the face when you have to pay $200 out of pocket to get each one fixed; Thus, the fear of paying for these procedures drives you to take better care of your teeth. As a result, I have not had a cavity in probably about 5 years. I used to slack off but learned my lesson through the wallet. Thus, its a win-win, you get better health for less money (since there are no premiums to pay).
I do go in to the dentist for 6-month checkups; my health insurance actually covers these checkups (but it does not cover any other dental procedures at all). Thus, this system has worked out great for me. I have no idea about that HSA stuff because I don't use it.