Broadly speaking there are three types of plans:
Indemnity plans (generally called dental insurance) allow employees to see any dentist who accepts this type of coverage.
Dental preferred provider organizations (PDPPO/PPO) provide in-network and out-of-network coverage.
Dental health managed organizations (DHMO) assign or allow employees to select an in-network dentist and/or in-network dental office and use the dental benefits in that network or managed-care plan.