Per the American Dental Association (ADA) Current Dental Terminology: The ADA Practical Guide to Dental Procedure Codes) [CDT] –
Nonduplication of Benefits – Term used to describe one of the ways the secondary carrier may calculate its portion of the payment if a patient is covered by two benefit plans. The secondary carrier calculates what it would have paid if it were the primary plan and subtracts what the other plan paid. For example, if the primary carrier paid 80 percent, and the secondary carrier normally covers 80 percent as well, the secondary carrier would not make any additional payment. If the primary carrier paid 50 percent, however, the secondary carrier would pay up to 30 percent.
Some dental benefit plans have "non-duplication of benefits" provisions. This means that the secondary plan will not pay any benefits if the primary plan paid the same or more than what the secondary plan allows for that dentist.
An example:
If both the primary and secondary carrier pay for the service at 80 percent level, yet the primary allows $100 and the secondary carrier normally allows $80 for the same treatment, the secondary carrier would not make any additional payment.
If the primary carrier only pays 50 percent of the dentist’s allowed fee, then the secondary carrier would reduce its payment by the amount paid by the primary plan and pay the difference. In this case, the secondary carrier would pay $14 ($80 x 80 percent - $50 = $14).