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N931 Remark Code: Pre/Post-Op Bitewing or PA Issue

N931 means the pre-operative and/or post-operative bitewing or periapical x-ray was missing, incomplete, or invalid. Payers use the before image to confirm the need for treatment and the after image to confirm the work was completed, for example a finished root canal fill.

Quick facts

Code
N931 (RARC N931)
Status
Active In use since July 1, 2026.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The unpaid amount pending acceptable before and after images. The dental office supplies them; the patient is not billed.
Official description
Missing/Incomplete/Invalid pre- and/or post-operative bitewing or periapical x-ray.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N931 means

Some dental procedures are judged on two moments: the condition that justified treatment, and the result. A pre-operative bitewing or periapical shows the problem. A post-operative image shows the outcome, such as root canals filled to the right length or a restoration seated properly.

N931 means one or both of those images is missing or cannot be used. It is narrower than N928, which only requires a bitewing or periapical, and narrower than N940, which does not name the view.

Common causes

  • Only the diagnostic image was sent; the completion image was left off.
  • The post-operative image was taken but not saved or exported.
  • The images do not show the same tooth, or are not labeled pre and post.
  • The dates do not align with the date of service.

How to fix it

  1. Check which image the payer is missing from the denial details.
  2. Export both images, labeled with patient, tooth, date, and pre or post.
  3. Send them together via the payer’s attachment process, referencing the claim.
  4. Request reprocessing or appeal if the claim has been finalized.

How to prevent it

For procedures where your major payers require completion images, add a checklist step so the post-operative image is captured and attached before the claim is released.

Codes that may appear with N931

  • CO-252 (An attachment/other documentation is required to adjudicate this claim/service.): An attachment is required; N931 names pre- and/or post-operative bitewing or periapical images.
  • CO-250 (The attachment/other documentation that was received was the incorrect attachment/document.): The wrong attachment was received, such as only the pre-operative image.
  • N928 (Missing/Incomplete/Invalid bitewing or periapical x-ray.): A bitewing or periapical is needed, without the before-and-after requirement.
  • N932 (Missing/Incomplete/Invalid pre- and/or post-operative full mouth x-ray.): Before-and-after full mouth series instead of individual images.
  • N940 (Missing/Incomplete/Invalid pre- and/or post-operative x-ray.): Before-and-after x-rays without naming the image type.

N931 FAQ

Which procedures need post-operative images?

Payers often want them for endodontic treatment, to show the canals are filled, and sometimes for implants or other surgical work. Policies vary by payer and procedure.

Do I need both images?

The remark says pre- and/or post-operative, so the payer may need one or both. Check what was already sent and what the payer's policy requires.

What if no post-op image was taken?

The payer may not pay without it. Taking a post-operative image purely for billing raises clinical and radiation questions, so decide based on clinical need and payer requirements.