Washington Revised Code Title 48. Insurance § 48.21.147. Dental services that are not subject to contract or provider agreement

(a) Require, directly or indirectly, that a dentist who is a participating provider provide services to a subscriber at a fee set by, or at a fee subject to the approval of, the disability insurer unless the dental services are covered services, including services that would be reimbursable but for the application of contractual limitations such as benefit maximums, deductibles, coinsurance, waiting periods, or frequency limitations, under the applicable group plan or disability insurance policy; nor

(b) Prohibit, directly or indirectly, a dentist who is a participating provider from offering or providing to a subscriber dental services that are not covered services on any terms or conditions acceptable to the dentist and the subscriber.