21 CFR §860.200

1. (a)The purpose of this part is to establish an efficient, transparent, and thorough process to facilitate De Novo classification into class I or class II for devices for which there is no legally marketed device on which to base a review of substantial equivalence and which meet the definition of class I or class II as described in section 513(a)(1) of the Federal Food, Drug, and Cosmetic Act and § 860.3.
2. (b)De Novo requests can be submitted for a single device type:
   1. (1)After receiving a not substantially equivalent determination in response to a premarket notification (510(k)), or
   2. (2)If a person determines there is no legally marketed device upon which to base a determination of substantial equivalence.