# Marginal Orbicularis Oris Hyperactivity (MOOH): An Exploratory Case Series of Inversion-Dominant Upper Lip Dynamics Following Intraoral Botulinum Toxin Type A

## TL;DR

This study explores a new type of lip movement causing gum visibility and shows that a small botulinum toxin injection can temporarily reduce this effect.

## Contribution

The paper introduces 'marginal orbicularis oris hyperactivity' as a novel dynamic contributor to gingival exposure and evaluates its modulation with botulinum toxin.

## Key findings

- Low-dose botulinum toxin reduced inversion-dominant lip dynamics in most patients.
- Functional changes were mild and temporary with preserved oral function.
- AIS and ΔLv% showed acceptable consistency as exploratory tools.

## 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.