CPT code 21127 denotes mandibular augmentation with bone grafting, a surgical procedure to enlarge or rebuild the lower jaw by placing graft material on the jaw bone or within its layers. The code captures both cosmetic augmentations and medically necessary reconstructions such as bite correction or structural restoration. This procedure is nationally relevant due to its intersection of reconstructive and cosmetic indications, implications for coverage determinations, and resource use in operating-room settings. Key payers covered in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will gain a concise clinical and billing profile of CPT code 21127, including typical sites of service and service classification, common modifier practices (listed separately), and the clinical contexts in which the code is used. The summary frames factors that influence payer coverage decisions, documentation expectations tied to medical necessity versus cosmetic intent, and where to locate related coding guidance. Data not available in the input: associated taxonomies, specific ICD-10 diagnosis pairings, payer-specific coverage policies, utilization benchmarks, and related codes. The content equips billing managers, clinicians, and policy analysts with a clear reference for understanding the clinical purpose of CPT code 21127 and the national payer landscape relevant to mandibular augmentation procedures.