When determining whether the claims of a patent are valid, the United States Patent and Trademark Office (Patent Office) typically reviews “prior art” published before the filing date of a patent application. Under the current first-to-file system in the US, however, any US patent or application that was filed before the application being reviewed can be considered prior art, even if the earlier-filed patent or application was not published before the filing date of the reviewed application. In a recent case, the Court of Appeals for the Federal Circuit (Federal Circuit), which hears appeals of all patent cases, clarified when patent applications qualify as prior art.

In this case, Align Technology challenged the validity of a Dental Monitoring patent in an inter partes review, citing one key prior art reference. Dental Monitoring’s patent had a filing date before the filing date of the cited prior art published patent application, but after the original, unpublished patent application from which the published patent application claimed priority. The Patent Office presumed that the published patent application qualified as prior art merely because it claimed priority back to the original, unpublished patent application. As a result, the Patent Office invalidated the claims of Dental Monitoring’s patent as obvious based on the published patent application. Dental Monitoring appealed this decision, arguing that one is required to analyze each claim of the published patent application to determine whether it can properly claim priority back to the original, unpublished patent application. The Federal Circuit agreed with Dental Monitoring and ruled that the original, unpublished patent application must actually provide sufficient written description support for at least one of the claims in the published patent application used to determine that the patent was invalid. The written description analysis requires that the specification of a patent describe the inventions claimed in the patent. This decision clarifies that the written description analysis is an important and required process to determine whether a patent or a patent application with a filing date after the filing date of the challenged patent can qualify as prior art by claiming priority back to an earlier-filed application.

The decision in this case could help patent owners defend against prior art in this type of situation if they can show that the later-filed patent application is not fully supported by the disclosure of the earlier-filed patent application from which it claims priority, and thus does not count as prior art.

The case is Dental Monitoring SAS v. Align Technology Inc., decided August 10, 2026. For more information, please contact the authors or your McCarter attorneys.

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