If your job offers insurance then yes you can.

However, I’m going to assume you’re referring to an individual policy. If that’s the case, then no. You must be 19 years old to take out your own personal policy. (I know it makes no sense) OR your other option is to have your parents take out a policy for you. They can take out a policy through BlueCross that is Dental Only for just you, then you can take over the policy when you’re 19 and in the meantime pay for it yourself, or have them add you back to their policy. You will fall off of their policy at age 22, then you can get your own.
Just a tip: Most PPO dental plans give you a waiting period of 6 months to 12 months. If you’re not picky about using your same dentist, you can get an HMO that would go into effect immediately.