Treating the DAO and Marionette Lines

The downturned mouth corner — what patients call a sad or angry resting expression — is one of the most anatomically instructive changes in facial ageing. It is not primarily a skin problem, and it is not primarily a volume problem. It is a neuromuscular imbalance: a progressive weakening of the muscles that lift the mouth corner, allowing a structurally intact but now relatively dominant depressor to pull the oral commissure inferiorly and laterally without adequate opposition. Treating this effectively requires understanding each layer of the process — and selecting interventions that address the right target.

Part One — What Actually Causes Marionette Lines

The Levator–Depressor Balance

The oral commissure is the meeting point of several muscular vectors that pull in opposing directions. The primary elevators of the mouth corner — the zygomaticus major, levator anguli oris (LAO), and levator labii superioris — act against the primary depressor, the depressor anguli oris (DAO), which originates along the inferior border of the mandible and inserts into the modiolus, a fibromuscular condensation at the lateral commissure that serves as a central anchoring point for multiple perioral muscles.^1,2

In youth, this muscular balance is maintained. The elevators are active, well-innervated, and supported by adequate bony and soft tissue architecture beneath them. The DAO is active but counterbalanced. What changes with age is not a sudden strengthening of the DAO — it is a progressive weakening of the elevators, combined with structural changes that shift the entire mechanical environment in the DAO's favour.^2,3

The result is a muscle that was always pulling down but was previously matched — now pulling down largely unopposed. The oral commissure descends. The skin lateral and inferior to the commissure is drawn downward and medially with it. The marionette line — the groove running from the commissure toward the chin — deepens not because the skin has folded, but because the soft tissue above and below the line has been displaced to different depths by different vectors.³

The Three-Layer Mechanism

Part Two — Treatment Options

Botulinum Toxin for the DAO

Botulinum toxin type A (BTX-A) injection into the DAO is the most anatomically direct intervention available for the downturned commissure. By reducing DAO contractile force, it partially restores the levator–depressor balance at the modiolus, allowing the residual elevator activity to express itself more effectively — lifting the mouth corner to a more neutral or subtly elevated resting position.^8,9

The results are modest but consistent: most patients experience a 1–3 mm elevation of the oral commissure at rest, with improvement in the resting expression that is perceptible to both the patient and observers.⁹ This is not a dramatic change in any individual treatment cycle, but it is reproducible, low-risk when performed correctly, and builds over multiple treatment cycles as the pattern of reduced DAO dominance becomes more established.

Injection Technique — Anatomy, Landmarks, and Dose

Accurate DAO injection requires careful landmark identification. The modiolus is the central reference point — palpated as a slightly firm, mobile fibromuscular knot at the oral commissure, approximately 1 cm lateral to the mouth corner. The DAO lies inferior and lateral to the modiolus, running diagonally from the mandibular border toward this insertion point.^1,2

The most significant technical risk in DAO injection is diffusion into the depressor labii inferioris (DLI), which lies medially and superiorly to the DAO and is responsible for depressing the central lower lip. Inadvertent DLI weakening produces asymmetric lip depression on animation — visible as an inability to pull the lower lip evenly downward when smiling broadly — and an asymmetric, flattened lower lip contour at rest that patients often find more concerning than the problem being treated.^9,10 Staying inferior to the commissure–mandibular line and using conservative doses on first treatment largely mitigates this risk.

A useful adjunct is the platysmal band assessment: the DAO is contiguous with the platysma at its inferior origin. In patients with prominent platysmal banding, co-treating the medial platysmal bands (nefertiti-style) at the same appointment can complement the DAO result by reducing the additional inferior pull of platysmal contraction on the lower face soft tissue.¹⁰

Platelet-Rich Plasma (PRP)

PRP does not address the muscular imbalance that drives marionette line formation — it is not a treatment for DAO dominance. What it does address is the dermal and soft tissue component of the problem: the collagen loss, the reduction in skin recoil, and the compromised extracellular matrix that allows the descended tissue to remain descended and that makes the marionette groove visible rather than transient.¹¹

When injected intradermally and subdermally along the marionette groove and into the pre-jowl region, the growth factors released from activated platelets — particularly TGF-β1, PDGF, and VEGF — stimulate dermal fibroblast proliferation, upregulate procollagen type I and type III synthesis, and promote neovascularisation.^11,12 The result is a measurable increase in dermal thickness and collagen density over the 3–6 months following treatment, with improvements in skin elasticity and surface texture that are objectively quantifiable on ultrasound and reflectance confocal microscopy.¹²

In the context of the marionette line, a thicker, better-supported dermis serves two purposes. First, it partially resists the soft tissue displacement that deepens the groove — a more structurally intact dermis does not deform as readily under the inferior traction of the DAO and gravity. Second, it improves the visual appearance of the groove directly by increasing dermal volume and improving skin surface light reflection in the affected zone.^11,12 PRP is not a stand-alone treatment for marionette lines — the muscular contribution must be addressed with BTX-A — but it is a rational complementary treatment for the dermal component, and the results of the two combined are more meaningful than either alone.

Red and Near-Infrared Light Therapy

Red and near-infrared (NIR) light therapy works through a fundamentally different pathway than PRP — not through growth factor delivery but through direct photobiomodulation of mitochondrial function in resident dermal cells. As described in the associated article on red light therapy mechanisms, the absorption of 630–700 nm red and 800–900 nm NIR photons by cytochrome c oxidase (Complex IV) in fibroblast mitochondria increases ATP production, activates downstream signalling cascades including NF-κB and TGF-β/Smad pathways, and directly upregulates collagen and elastin gene expression.^13,14

For the lower face and marionette line zone specifically, the tissue penetration of NIR wavelengths (800–900 nm, penetrating 20–40 mm) is sufficient to reach the dermal fibroblasts and sub-dermal connective tissue at the depth where the marionette groove is anchored.¹³ The collagen synthesis stimulation is not dramatic in any single session, but it is cumulative — regular treatment over 8–12 weeks produces measurable increases in collagen density and skin thickness, with clinical improvements in line depth and skin laxity consistent with the mechanism.^14,15

Red/NIR light therapy is well-suited as an ongoing maintenance strategy between PRP treatments. It carries no downtime, no injection risk, and can be performed regularly. In a patient receiving DAO botulinum toxin every 3–4 months and PRP 1–2 times per year, red/NIR light therapy in the intervening period provides a continuous collagen stimulus that supports and prolongs the structural improvements achieved by PRP.¹⁵

Part Three — Why This Practice Does Not Use Filler for Marionette Lines

Filler — specifically hyaluronic acid (HA) filler — is widely used by practitioners for marionette lines, typically injected along the groove itself or in the pre-jowl sulcus to create volume and reduce the visual depth of the line. I do not prescribe filler for this indication, and the reasons are both philosophical and evidence-based.

The Philosophy: Adding Volume in the Wrong Direction

The marionette line is formed, in part, by the inferior displacement of tissue that was previously in a more superior position. The jowl that deepens the marionette groove is descended cheek fat — volume that has moved down from where it belonged. Injecting filler into the marionette groove or the pre-jowl sulcus adds volume inferior to its natural position. It may mask the groove in the short term, but it does so by adding more mass to a region already burdened by excess descended volume — and it does nothing to address the muscular, ligamentous, or dermal mechanisms driving the change.¹⁶

This matters for two reasons. First, the result is often unconvincing on close inspection: filling a groove whose edges are themselves in the wrong position tends to produce a blunted, heavy lower face rather than a restored one. Second — and more importantly — it adds material to a dynamic anatomical zone that is subject to ongoing muscular movement, gravitational displacement, and lymphatic forces, all of which influence where that material goes over time.

The Evidence: Filler Migration and Retention

The traditional narrative around HA filler was that it was temporary — degraded by hyaluronidase over 6–18 months and safely absorbed. This narrative is not supported by the imaging evidence.

The most compelling imaging evidence comes from Australian oculoplastic and cosmetic surgeon Mobin Master and colleagues, whose body of work using MRI to evaluate HA filler in the mid-face is now among the most cited in discussions of filler longevity. Their 2024 study in Plastic and Reconstructive Surgery — Global Open reviewed MRI scans from 33 patients who had received mid-face HA filler, assessed by two blinded radiologists.¹⁶ The findings were unambiguous: filler was detectable in all 33 patients, with no cases of complete dissipation. Of those 33 patients, 21 had not been injected for 2–5 years, 12 had not been injected for over 5 years, and some patients had measurable filler retention 8–15 years after their last treatment. The statistical confidence interval for longevity was 95% CI of 84.47% ± 4.43%. Filler volumes were classified as mild in 9 patients, moderate in 13, and severe in 11 — the latter group including patients with oedema and symptomatic presentations despite having received what would be considered standard cosmetic doses.^16,17

This is not a hypothetical or theoretical risk — it is an observable phenomenon documented on MRI in real patients treated by qualified practitioners, often years or decades prior to imaging. The second finding from this body of work is filler migration: material identified at anatomical locations distinct from the documented injection sites, having tracked along tissue planes, fascial boundaries, and lymphatic pathways into regions that had never been treated.¹⁶

These findings are consistent with independent histological and imaging research. Goldie et al. identified persistent HA deposits in facial tissue on histology years after injection, with evidence of encapsulation and tissue reaction.¹⁸ Funt and Pavicic identified migration patterns along the SMAS and sub-SMAS planes as a mechanism by which filler tracks inferiorly under gravity and muscular activity.¹⁹ Wongprasert et al. demonstrated HA persistence of greater than 2 years in periorbital and cheek tissue on MRI, significantly beyond the expected duration.²⁰

In the lower face specifically, the marionette and pre-jowl region is a high-movement zone — subject to chewing, speaking, swallowing, and the repeated inferior pull of the DAO and platysma. These forces actively displace injectable material over time. Filler injected into this region has a particularly high likelihood of tracking inferiorly toward the neck, or medially toward the chin and submental region, producing the characteristic "pillow face" or "heavy lower face" appearance that becomes visible years after treatment in patients who received filler regularly in their thirties and forties.^19,21

Part Four — Putting It Together

Effective management of the downturned commissure and marionette line requires layered thinking. The neuromuscular imbalance — DAO dominance — is addressed with BTX-A, which is the most direct, evidence-based, and anatomically specific intervention available. The dermal and connective tissue component — collagen loss, skin laxity, reduced dermal support — is addressed through PRP and ongoing red/NIR light therapy, which work through different but complementary mechanisms to restore dermal architecture over time. The jowl and SMAS components that contribute to the overall morphology are addressed through patient education about realistic expectations: without surgical repositioning of the descended soft tissue, the three-dimensional volume shift of a significant jowl cannot be fully corrected through injectable or energy-based means alone.

What this approach does not include is filler. Not because filler cannot change the appearance of a marionette line — it can, transiently. But because the weight of imaging evidence now clearly demonstrates that HA filler does not behave as a temporary, precisely located implant. It persists, it migrates, and it accumulates in tissue planes that were not the intended target. For a region that is already anatomically complex, mechanically active, and carrying the functional deficit of a muscular imbalance, adding material with uncertain long-term behaviour is not a trade-off this practice is willing to make on a patient's behalf.