Short answer: Yes. In the Marketplace you can choose a health plan that includes dental, or buy a separate stand-alone dental plan, but you can only buy Marketplace dental if you are also enrolling in a health plan. A separate dental plan has its own premium, and adult dental plans may have waiting periods.
In the Marketplace, you can pick a health plan with or without dental benefits. If the health plan includes dental, one premium covers both. If it does not, you can add a separate dental plan, which you will see when you compare plans, for an extra premium. You cannot buy a Marketplace dental plan on its own, only alongside a health plan.
Children’s dental must be available because it is an essential health benefit; adult dental is optional and not guaranteed. Stand-alone dental plans can impose waiting periods before they start covering adult services, and you still pay premiums during that wait, so confirm the waiting periods and covered services with the insurer before you enroll.