2026 ICD-10-CM Diagnosis Code M26.31Crowding of fully erupted teeth

ICD-10-CM Codes›M00–M99›M26-M27›M26

ICD-10-CM M26.31
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M26.31 is a billable ICD-10-CM diagnosis code for crowding of fully erupted teeth. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 157 through 159. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Any dental condition including traumatic injury, Disorders of jaw, and Disorders of teeth and gingiva.

Code Identity

ICD-10-CM Code
M26.31
Billable Status
Yes — Valid for Submission
Code Describes
Crowding of fully erupted teeth
Short Description
Crowding of fully erupted teeth
Same as the full description in the CMS dataset.
Parent Code
M26.3
Anomalies of tooth position of fully erupted tooth or teeth

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM26-M27Dentofacial anomalies [including malocclusion] and other disorders of jaw
CategoryM26Dentofacial anomalies [including malocclusion]
This CodeM26.31Crowding of fully erupted teeth

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Anterior imbrication of teeth
  • Crowding of anterior mandibular teeth
  • Crowding of anterior maxillary teeth
  • Crowding of posterior mandibular teeth
  • Crowding of posterior maxillary teeth
  • Crowding of teeth
  • Crowding of teeth due to supernumerary teeth
  • Posterior imbrication of teeth

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Crowding, tooth, teeth, fully erupted

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR DEN001
Any dental condition including traumatic injury
Default principal diagnosis: inpatient No · outpatient No
CCSR MUS029
Disorders of jaw
Default principal diagnosis: inpatient Yes · outpatient Yes
CCSR DIG002
Disorders of teeth and gingiva
Default principal diagnosis: inpatient No · outpatient No
CCSR DEN002
Nontraumatic dental conditions
Default principal diagnosis: inpatient No · outpatient No

Patient EducationClinical

Tooth Disorders

Your teeth are made of a hard, bonelike material. There are four parts:

The full article covers:

  • What are teeth?
  • What are tooth disorders?
  • What causes tooth disorders?
  • What are the symptoms of tooth disorders?
  • How are tooth disorders diagnosed?
  • What are the treatments for tooth disorders?
  • Can tooth disorders be prevented?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert M26.31 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
524.31 Crowding of teeth
Exact Match The mapping is direct, with no qualifiers.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M26.31Overview

Is M26.31 (Anomalies of tooth position of fully erupted tooth or teeth) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report crowding of fully erupted teeth on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M26.31 group to?

When crowding of fully erupted teeth is the principal diagnosis on an inpatient stay, it groups to MS-DRG 157, 158, 159, with relative weights from 0.7085 to 1.7168 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M26.31?

Under the General Equivalence Mappings, crowding of fully erupted teeth converts to ICD-9-CM 524.31 (crowding of teeth). The mapping is a direct match.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.