M26.12 identifies jaw asymmetry that is not attributable to maxillary asymmetry (M26.11), capturing mandibular laterognathia and other non-maxillary imbalances in jaw-cranial base relationship.
Verified May 8, 2026 · 4 sources ↓
- Status
- Billable
- Chapter
- 13
- Related CPT
- 12
- Region
- Other
Documentation tips
What should appear in the chart to support M26.12.
Source · Editorial brief grounded in 4 cited references ↓
- Specify which jaw structure is asymmetric — mandible, chin, or other non-maxillary structure — to distinguish M26.12 from M26.11 (maxillary asymmetry).
- Record imaging findings (cephalometric radiographs, CBCT, or panoramic X-ray) that quantify skeletal deviation, including midline shift measurements when available.
- Document functional impact: occlusal discrepancy, midline deviation on opening, limited range of motion, or masticatory dysfunction support medical necessity and enable concurrent coding.
- If condylar hyperplasia or hypoplasia is identified on imaging, the provider must explicitly confirm or exclude M27.8 before M26.12 is assigned — the Type 1 Excludes note makes these mutually exclusive.
- For surgical cases, ensure the operative report and pre-op evaluation use consistent language matching the diagnosis — 'mandibular laterognathia' or 'jaw asymmetry' maps cleanly to M26.12; 'hemifacial microsomia' may route elsewhere.
Related CPT procedures
Procedure codes commonly billed with M26.12. 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 M26.12 and adjacent codes.
Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓
- Assigning M26.12 when documentation clearly identifies maxillary asymmetry — that presentation requires M26.11, not M26.12.
- Ignoring the Type 1 Excludes for unilateral condylar hyperplasia or hypoplasia (M27.8); these conditions cannot be coded alongside M26.12 — M27.8 replaces it when condylar pathology is documented.
- Coding M26.12 alongside Q67.4 (hemifacial atrophy or hypertrophy) — the section-level Type 1 Excludes bars both codes from appearing together on the same claim.
- Using M26.10 (unspecified anomaly of jaw-cranial base relationship) when the provider has documented a specific non-maxillary asymmetry — M26.12 is the more specific and payable code in that scenario.
Clinical context
Source · Editorial summary grounded in 4 cited references ↓
M26.12 sits within the M26.1 subcategory (anomalies of jaw-cranial base relationship) and is the correct code when documented jaw asymmetry involves the mandible or a structure other than the maxilla. The sibling code M26.11 covers maxillary asymmetry specifically; if the provider documents maxillary involvement, use M26.11 instead. M26.12 is the residual code for everything else in this subcategory — mandibular laterognathia, asymmetry of the inferior border of the mandible, or generalized jaw asymmetry where the maxilla is not identified as the source.
The M26-M27 section carries a Type 1 Excludes for hemifacial atrophy or hypertrophy (Q67.4) and unilateral condylar hyperplasia or hypoplasia (M27.8). If imaging or clinical documentation supports either of those specific diagnoses, they displace M26.12 entirely — you cannot code both. Confirm that the provider's diagnosis language does not describe condylar hyperplasia/hypoplasia before assigning M26.12.
M26.12 groups into MS-DRG v43.0 clusters 157–159 (Dental and oral diseases with/without CC/MCC) for inpatient claims. It is commonly paired with orthognathic surgery CPT codes when asymmetry is the operative indication, and with imaging codes to support pre-surgical planning or diagnosis confirmation. Document whether the asymmetry is functional (affecting occlusion, mastication, or mandibular range of motion) or purely skeletal, as concurrent codes such as M26.51 (abnormal jaw closure) or M26.52 (limited mandibular range of motion) may be warranted.
Sibling codes
Other billable codes under M26.1 (laterality / anatomic variants).
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 4 cited references ↓
01What is the difference between M26.11 and M26.12?
02Can M26.12 be used when condylar hyperplasia is the underlying cause?
03Is M26.12 appropriate for hemifacial microsomia?
04Which CPT codes are commonly billed with M26.12?
05Does M26.12 require a 7th-character extension?
06Can M26.12 be coded with TMJ disorder codes such as M26.61?
07What MS-DRG does M26.12 map to for inpatient claims?
Sources & references
Editorial content was developed using the following public sources. Last verified May 8, 2026.
- 01CDC ICD-10-CM Tabular List 2026 (effective October 1, 2025)
- 02icd10data.comhttps://www.icd10data.com/ICD10CM/Codes/M00-M99/M26-M27/M26-/M26.12
- 03aapc.comhttps://www.aapc.com/codes/icd-10-codes/M26.12
- 04findacode.comhttps://www.findacode.com/icd-10-cm/icd-10-cm-diagnosis-codes-M26-group.html
Mira AI Scribe
Mira's AI scribe captures the provider's identification of the asymmetric jaw structure (mandible, chin, or other non-maxillary component), any midline deviation measurement, imaging modality and findings (CBCT, cephalometric, panoramic), and documented functional sequelae such as occlusal shift or limited opening. This prevents a drop to the unspecified M26.10, avoids a Type 1 Excludes conflict with M27.8 or Q67.4, and supplies the medical-necessity detail payers require for orthognathic surgery authorization.
See how Mira captures M26.12 documentation