Marginal Orbicularis Oris Hyperactivity (MOOH): An Exploratory Case Series of Inversion-Dominant Upper Lip Dynamics Following Intraoral Botulinum Toxin Type A
Year: 2026
Type: article
Abstract: Excessive gingival display (EGD) is most commonly attributed to vertical upper lip elevation, short lip length, or dentoalveolar disproportion. However, some patients exhibit gingival or mucosal visibility during smiling despite minimal vertical upper lip displacement, suggesting the presence of alternative dynamic patterns. This exploratory case series examined an inversion-dominant smile presentation and its documented modulation in association with conservative intraoral chemodenervation directed toward the marginal region of the orbicularis oris. Ninety-four patients with dynamic inversion during smiling were assessed using a qualitative rating aid (Armenti Inversion Scale, AIS) and a quantitative composite proportional measure of vermilion loss (ΔLv%). All patients received low-dose intraoral Onabotulinum toxin A (4-6 U) as part of routine aesthetic care. At Day 15 follow-up, a shift toward lower inversion grades was observed across the cohort, with a large proportion of patients showing minimal residual inversion. Quantitative ΔLv% values showed proportional changes that were directionally consistent with shifts in AIS grade. The functional alterations were mild, transient, and self-resolving. Preliminary inter-rater agreement for AIS and measurement repeatability for ΔLv% suggested acceptable internal consistency for exploratory reporting tools. These findings suggest that inward vermilion inversion may represent a potentially distinct dynamic contributor to gingival or mucosal exposure in selected individuals, and that conservative marginal chemodenervation was associated with transient modulation of this pattern with generally preserved oral competence. AIS and ΔLv% are preliminary documentation tools. Further studies incorporating objective neuromuscular assessment, three-dimensional imaging, and comparative designs are required to refine phenotypic characterization.
Source: Toxins
Author: Andrea Felice Armenti
Language: English
Subfield: Orthodontics
Field: Dentistry
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $3,258
OpenAlex ID: W7138351011