Botulinum Toxin Type A for Gummy Smile: Anatomical Targeting, Protocol Variability, and Reproducible Outcome Measurement

Abstract

Background: Botulinum toxin type A (BoNT/A) can reduce excessive gingival display in selected muscular phenotypes, but the literature remains difficult to compare because anatomical assumptions, protocol reporting, and endpoint capture are uneven.

Objective: To critically reassess the use of BoNT/A for gummy smile, with emphasis on the Yonsei point, and to identify the variables that most strongly determine reproducible clinical response.

Methods: Structured critical narrative review integrating etiologic phenotyping, upper-lip elevator anatomy, BoNT/A formulation and preparation variables, clinical injection studies, and the measurement science underlying standardized photography and three-dimensional facial imaging.

Results: Current evidence supports temporary reduction of gingival display in selected muscular cases and provides a credible anatomical rationale for Yonsei-region targeting. However, the landmark is not universally transferable, and cross-study interpretation remains constrained by phenotype heterogeneity, incomplete reporting of dilution-volume-depth parameters, and weakly standardized photographic endpoints. Protocolized two-dimensional imaging can be reliable, whereas three-dimensional surface imaging generally provides lower geometric error when available. Longitudinal reading of Yonsei-derived publications suggests continuity of anatomical reasoning but slower progress in endpoint harmonization and formal reproducibility standards.

Conclusion: BoNT/A remains a defensible minimally invasive option for compatible muscular etiologies, but reproducible evidence depends on treating anatomy, product handling, injection mapping, and outcome capture as one protocol rather than as separate variables. The next substantive advance is standardized phenotyping linked to calibrated measurement, traceable documentation, and reproducible endpoint definition.