Dental crowding in which fully erupted permanent teeth lack adequate arch space, causing overlapping, displacement, or malalignment of teeth that have already completely emerged through the gingiva.

Documentation tips

What should appear in the chart to support M26.31.

Source · Editorial brief grounded in 5 cited references ↓

• Confirm in the note that the affected teeth are fully erupted — not partially erupted or impacted — before assigning M26.31.
• Specify which arch is affected (maxillary, mandibular, or both) and whether crowding is anterior, posterior, or generalized, to support medical necessity.
• If crowding coexists with an impacted tooth, separately document the impaction and assign K01.- alongside M26.31 — the Type 2 Excludes permits dual coding when both conditions are present.
• Include any radiographic findings (panoramic X-ray, CBCT) that confirm insufficient arch length or tooth-size discrepancy to strengthen audit defense.
• Document the clinical rationale for treatment (e.g., extraction planned, orthodontic surgical referral) tied directly to the crowding diagnosis.

Related CPT procedures

Procedure codes commonly billed with M26.31. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

Common coding pitfalls

The recurring mistakes coders make with M26.31 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Billing M26.3 (the non-billable parent) instead of M26.31 — M26.3 lacks the specificity required for reimbursement and will be rejected.
• Using M26.31 for partially erupted or impacted teeth — those cases belong under K01.- (Embedded and impacted teeth), not M26.3x.
• Confusing crowding (M26.31) with excessive spacing (M26.32) or horizontal displacement (M26.33) — each is a distinct positional anomaly with its own billable code; match the code to the documented finding.
• Omitting a secondary K01.- code when an impacted tooth is also documented — the Type 2 Excludes permits dual coding, and failing to capture the impaction may underrepresent diagnosis complexity.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M26.3 (laterality / anatomic variants).