Watch a smiling patient stop smiling for a second. The corners of the mouth don’t just fall, they are pulled down by a tug-of-war between the depressor anguli oris (DAO) and the levator complex, especially the depressor labii inferioris (DLI) and mentalis. When the DAO dominates, marionette shadows deepen, lipstick bleeds into vertical perioral lines, and the resting face reads tired or stern. Calibrated Botox use in this zone is not about “freezing.” It is selective weakening, with intent to rebalance vectors and protect function. In practice, that means knowing where these fibers live, how they behave in your patient, and how a unit here or a half unit there changes the way their smile lands.
The functional map: DAO and DLI in real faces
The DAO originates along the mandibular body and inserts at the modiolus at the mouth corner. It pulls the commissure down and slightly lateral. The DLI sits medial and deeper, depression-focused on the lower lip itself. Over-treat DAO and the DLI can overexpress, causing a crooked, “tucked” lower lip on speech. Treat DLI by accident and you invite lower lip incompetence, difficulty with “f” and “v” sounds, and straw use problems.
In animation testing, I ask for three moves: a tight “e,” a strong “sad face,” and a slow, tooth-baring smile. In the “sad face,” the DAO bands become obvious as vertical cords lateral to the marionette line. In the tight “e,” DLI action presents as lower lip flattening and central depression. This animation analysis, done from frontal and oblique angles, is the best predictor of injection placement success. It also defines asymmetry. One side often wins, and you want to anticipate compensatory drift in the weeks after Botox onset.
Dosing logic for DAO: ranges and rationale
For most adult faces, DAO dosing ranges from 2 to 4 units of onabotulinumtoxinA per point, 2 points per side, with a total of 8 to 16 units for both sides combined. Petite faces or first-time patients may start at 1 to 2 units per point. Male faces or high-mass lower faces can need 3 to 5 units per point, especially if there is strong clenching, a heavy masseter set, or a downturn at rest. I rarely exceed 20 units total to the DAO complex on both sides unless I am splitting doses over staged sessions, and only after checking how the lips perform during speech.
The DLI is not an automatic target. Direct DLI treatment is reserved for patients with hyperdepressed lower lip and gummy lower smile imbalance, or for correction after a prior imbalance created by DAO dosing. If I treat DLI, I do so conservatively: 0.5 to 1.5 units per side, one precise point, superficial to mid-depth, avoiding diffusion toward the mental foramen and orbicularis oris. Most patients do not need DLI dosing.
Landmarks that keep you out of trouble
With the patient sitting upright, trace a line from the lateral canthus to the mouth corner. The DAO action point sits just inferior and lateral to the corner, typically 1 to 1.5 centimeters below the commissure, superficial to mid-depth. I palpate while the patient exaggerates a downturn; you can feel the band tighten under the skin. I mark two points along that band, roughly in a vertical line, spaced 5 to 8 millimeters apart. Staying lateral is safer. Medial drift risks DLI and orbicularis oris influence.
The mental foramen typically lies along a vertical line aligned with the pupil, about 1.5 to 2.0 centimeters inferior to the lower vermilion, near the midbody of the mandible. Avoid this area to reduce risk of temporary paresthesia or uneven diffusion. Respect vascular landmarks as well: the facial artery crosses near the mandibular border anterior to the masseter. Gentle aspiration is not reliable with such small needles and volumes, so the aim is controlled, slow deposition at safe planes and distances.
Injection depth and diffusion control
DAO fibers are superficial to mid. I use a 30- or 32-gauge half-inch needle and a perpendicular to slightly oblique angle. The sweet spot is intramuscular without deep plunge. If you see blanching, you are likely too superficial in dermis; if you feel periosteal scrape, you are too deep and may increase spread. A small volume per point reduces diffusion spread: 0.02 to 0.04 mL if using typical reconstitution. Spacing points 5 to 10 millimeters apart allows coverage without confluent fields that soften or “smudge” the smile.
Dilution ratios matter. With onabotulinumtoxinA, a common dilution is 2.5 mL per 100 units. For the perioral zone, I often prefer 1 to 2 mL per 100 units to tighten the spread. Lower volume per unit produces more predictable focal effects. If you need a larger field, add points, not volume.
Microdosing for mouth corners that collapse in motion
Some patients only show downturn in dynamic speech or photo laughter. Microdosing works for them. Think 0.5 to 1 unit per point at two points per side, review at two weeks, then add another 0.5 to 1 unit only where needed. This approach preserves the levator balance and protects speech. It also reduces the risk of “joker lip,” a flat, unresponsive corner that looks numb in video calls. It takes patience and good documentation, but it lands a natural result.
Asymmetry: strategy before the syringe
If the right corner drops more, treat the right DAO slightly stronger or bring the left down just a touch to match. I prefer strengthening the weaker side’s lift indirectly, not by over-relaxing the stable side. A typical plan: 3 units per point on the dominant-drop side, 2 units per point on the other. Reevaluate in two weeks for a 0.5 to 1 unit micro-top-up. Avoid chasing symmetry in one visit, especially in expressive personalities where compensatory patterns are robust.
Speech assessment matters here. Ask the patient to say “fifty-five” and “vacation.” If the lower lip feels heavy after prior treatments, defer DLI and lighten DAO. On follow-up, consider a tiny mentalis point to smooth pebbling if the chin is overcompensating.
DAO, DLI, and mentalis: triad thinking
The mentalis stabilizes the chin and lower lip. Overactive mentalis creates chin dimpling and an upward push that can look like pouting. When you relax DAO, mentalis sometimes activates to maintain oral competence during speech or swallowing. If dimpling worsens after DAO treatment, a conservative mentalis dose of 2 to 5 units split across two midline points can help. The injection plane is intramuscular, just above the bony prominence, with shallow to mid-depth passes to avoid deep spread along the periosteum.
The DLI is the third voice. If the lower lip tucks or speech sounds slur post-DAO, do not add more DAO. Reassess for DLI over-activity and consider the smallest corrective dose, or wait for partial washout. Most issues improve as the brain relearns balanced recruitment.
Sequencing around fillers and skin quality
Perioral filler can support marionette shadows and the pre-jowl sulcus after DAO relaxation. I prefer to perform Botox first, wait two weeks, then place filler in a lighter hand because the muscle tone has changed. Hyaluronic acid in the marionette line responds well when the downward pull is reduced. If the skin shows fine vertical rhytids, microdroplet Botox in orbicularis oris can help, but stay minimal. For speech safety, microdose with 0.5 to 1 unit spaced by at least a centimeter, and avoid crossing the midline near the philtrum.
Texture improvements from Botox are real but modest in this region. Patients may report smoother makeup lay and a slight decrease in oil around the corners. Wrinkle depth changes depend more on mechanical load reduction than direct dermal effects. Expect small gains here, larger when combined with topical retinoids and energy-based tightening over months.
Longevity, metabolism, and muscle strength
Most perioral treatments last about 8 to 10 weeks because these muscles move constantly. Athletes, heavy talkers, and those with high muscle mass can see shorter durations, sometimes 6 to 8 weeks. The DAO experiences more constant activation in frown-prone or stress-grinding patients. Plan maintenance at 8 to 12 week intervals. If a patient reliably wears off by week 6, consider incremental unit increases of 10 to 20 percent, or splitting sessions: a light first pass and a scheduled touch-up at two weeks to build effect without spillover.
Exercise intensity affects longevity modestly. High-intensity interval training enthusiasts often report shorter spans by a week or two. Encourage consistent schedules and realistic expectations. Dilution does not change biologic duration when dosing is equivalent, but lower-volume injections reduce unwanted diffusion, which patients perceive as better quality and, indirectly, “longer” results.
Avoiding complications: the perioral safety net
The biggest functional risks in this zone are smile asymmetry and lower lip incompetence. Both are preventable with conservative dosing, lateral placement, and staged adjustments. Stay away from the vermilion border by at least 1 centimeter when addressing DAO. Keep the injection plane controlled to avoid seeding into orbicularis oris. Use small volumes and adequate point spacing to control diffusion spread.
Vascular safety is usually straightforward given the small doses, yet respect bruising risk in patients on anticoagulants or supplements like fish oil. Ice and gentle pressure help. If bruising occurs, it is self-limiting. For pain-sensitive patients, a topical anesthetic dulls the first pass, but numbing cream can obscure micro-landmarks. I often skip it and rely on slow injection and distraction.
Eyelid or brow ptosis ties more to glabellar or forehead work than perioral treatment, but remember multi-zone sessions can interact. If you are treating the upper face the same day, maintain clean unit mapping for forehead and glabellar lines, and avoid low, central frontalis points that could drag brows when DAO dampening slightly reduces lower-face opposition. Balanced vectors protect overall expression.
DAO in the context of the whole face
The corners of the mouth do not live in isolation. Heavy masseters create a square lower face and can exaggerate the visual downturn by adding weight laterally. In patients with bruxism, masseter dosing between 20 and 30 units per side can slim and reduce clenching pain, indirectly improving perioral harmony. Cheek volume also matters. Flatness at the anterior cheek makes marionette shadows read deeper. In such cases, modest cheek support with filler reduces the need for higher DAO dosing.
Crow’s feet treatments must respect cheek dynamics to avoid flattening smiles. Use lateral orbicularis points that favor a gentle fan pattern and stop short of the malar eminence. Uprighting the mouth corners without preserving cheek pop yields a strange, disconnected smile. Seek coherent movement across zones.
Technique pearls that change outcomes
I chart pre- and post-treatment muscle testing: photographs in rest, “sad face,” “e” sound, and full smile. On review day, I add the same set. It clarifies whether an odd look comes from DLI, mentalis, or residual DAO. Patients appreciate objective visuals and are more willing to accept staged micro-adjustments.
I prefer a slight medial-to-lateral needle angle when treating the DAO, parking the bevel at mid-depth. The hand position is steady with minimal excursion, depositing tiny aliquots rather than one bolus. If I see the corner curl under during speech with teeth hidden, I stop and reevaluate before placing any DLI dose. That restraint prevents most speech complaints.
When treating expressive personalities, I use preventative microdosing in high-movement zones. Two micro points per side for DAO at 0.5 to 1 unit each can stave off deep marionette etching without freezing natural expressivity. Over time, patients develop lighter resting tone, which can lengthen intervals slightly. I discuss this as muscle retraining rather than permanent change. Long-term atrophy is possible with repeated sessions, but in small perioral muscles it tends to be modest and rarely problematic if dosing remains conservative.
Adapting to first-time and repeat patients
First-timers often respond briskly to smaller doses. Start light, aim for harmony, then build. Repeat patients reveal their metabolism patterns. If a patient reports excellent effect that fades at week 8 like clockwork, book them at 10 weeks and accept slight overlap loss rather than chasing a 12 to 14 week ideal. If effect is weak at two weeks, check for true resistance. True primary nonresponse is rare. Secondary resistance can develop with frequent, high-dose, short-interval treatments, particularly with older formulations or switching brands without accounting for unit conversion. Before suspecting resistance, rule out underdosing, heavy muscle dominance, and improper placement.
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When resistance is likely, options include switching to a different botulinum toxin formulation, adjusting dilution to target spread, and timing treatments at longer intervals to reduce antigenic load. Add electromyography in complex cases where muscle recruitment is unclear. But in the DAO and DLI zone, better mapping usually beats brute doses.
Diffusion, spacing, and onset timing
Onset around the mouth is quick. Patients notice changes in 48 to 72 hours, with full effect by day 7 to 10. The perioral area moves constantly, which helps distribute the toxin at the synaptic level. That speed is helpful for planning touch-ups. I invite patients back at day 10 to 14, not sooner, to allow full settling. Most top-ups are 0.5 to 2 units per side.
Injection spacing of at least 5 millimeters between points is enough in this small field. Overlapping halos create excessive flattening. When in doubt, leave a half unit on the table and use the follow-up visit.
Managing edge cases
Thin skin patients bruise more and often show minor asymmetry more clearly. Reduce volume, use the smallest practical needle, and avoid swiping across planes. Slow injections help prevent tracking along superficial lines. For older patients with low skin elasticity and etched marionette lines, Botox alone will not lift the corner. Pair with filler, sometimes with a tiny cannula-deposited bolus near the modiolus plane, keeping clear of the facial artery. The toxin reduces the downward pull, the filler fills the shadow.
Male anatomy, with heavier lower-face mass and broader mandibular angles, often needs higher per-point dosing. Aim to preserve a hint of corner downturn to maintain a natural masculine expression. Over-corrected corners look stylized.
If a patient presents after a poorly placed treatment elsewhere with slurred speech or pronounced lower lip drop, support them. Explain expected washout, avoid additional lower-face toxin, and consider small mentalis support only if the chin is overacting. Most functional issues fade within 4 to 6 weeks as synapses regenerate.
Interplay with smile patterns and emotional expression
Botox impacts emotional read-through. Relaxing DAO softens the default “resting frown.” That shift can be a goal, especially for high-stress professionals who carry tension at the corners. I discuss this explicitly. We want pleasant neutrality, not a forced upturn that mismatches mood. A half unit difference at the lateral point can be the difference between approachable and artificial. Keep alignment with the patient’s profession and daily expressivity. Performers, teachers, and customer-facing roles need crisp enunciation and clear lower lip mobility. Err on the side of microdosing for them.
Storage, handling, and why it matters to results
Potency starts at the fridge. Keep vials at recommended temperatures and reconstitute with preservative-free saline. Gently swirl rather than shake. Label dilution clearly. For lower-face precision, tighter dilutions allow smaller volumes per unit, which in turn reduce diffusion. If you work across several areas in one session, prepare separate syringes for perioral use to avoid mix-ups. These mundane steps prevent most “mystery” results.
The broader plan: prevention, maintenance, and aging patterns
Mouth corner downturn deepens with cumulative load: repeated frowning, tooth wear, masseter hypertrophy, and skin laxity. Preventative use makes sense once subtle pull appears, not before the face moves. Patients in their early thirties with new marionette shadows can benefit from microdoses that keep DAO from etching lines while preserving normal animation. Over time, you may see slower formation of static lines. Do not promise wrinkle erasure, promise better balance.
For long-term maintenance, many settle into 3 to 5 sessions per year for the lower face, less if combined with structural support. Touch-ups should be small and planned, not panic fixes. Document unit maps and muscle responses. Stable maps yield stable outcomes, but be ready to adjust for weight changes, dental work, or a new exercise regimen, all of which can shift muscle dynamics.
Practical checkpoints before you inject
- Confirm dominant side by “sad face,” “e,” and full smile, then mark two DAO points per side, lateral to the modiolus by at least 1 centimeter. Choose a tight dilution for perioral precision, and limit volume per point to reduce diffusion. Start low on first treatments, especially in thin faces or high-communication professions; plan a 10 to 14 day review. Keep injections superficial to mid-depth, avoid the mental foramen zone, and steer clear of orbicularis oris unless intentionally microtreating perioral lines. Document unit mapping and take standardized expression photos to guide future fine-tuning.
When DAO treatment intersects with other zones
Glabellar and forehead work affect how the lower face is perceived. If brows are pulled heavy from low frontalis points, the mouth corners appear more downturned by contrast. Respect safety margins near the orbital and periorbital area, and map units in the forehead to prevent brow drop. Tailor to muscle strength testing; thicker frontalis often tolerates a modest lift pattern by keeping lateral points higher.
Nasal dynamics add another layer. Bunny lines can be microtreated along the nasalis with 2 to 4 units per side, but too much can flatten midface expression and shift attention to the Greensboro NC botox providers mouth corners. For strong nasal flaring, tiny points along alar base can balance a gummy smile, but again, precision wins. For a gummy smile, target levator labii superioris alaeque nasi with microdoses, keeping speech intact.
Outcome tracking and patient education
Set expectations early. Onset by day 2 to 3, full effect by day 7 to 10. Likely duration 8 to 10 weeks in the mouth corner region. Explain the possibility of a minor tweak botox NC at the two-week mark. Make clear the signs of over-relaxation: difficulty with “f” and “v,” straw use challenge, and asymmetrical pull during “e.” Most are avoidable and, if present, transient.
I encourage patients to take three short phone videos at home in consistent lighting: neutral rest, saying “fifty-five vacation,” and a big smile. They send these at day 10. Seeing movement in motion helps me refine more than photos alone. Over several cycles, the map becomes their map. That is how you achieve consistent outcomes while keeping expressions alive.
Final thoughts from the chair
The DAO and DLI look simple in a textbook. In the chair, they tell different stories in every face. Precision Botox here is less about a recipe and more about listening to how the face speaks when it is not speaking. Conservative dosing, tight dilution, and disciplined mapping let you nudge corners up without stealing words or warmth. When you align technique with anatomy and a patient’s expressive identity, a few carefully placed units can change how their day greets them in the mirror, and how the world reads their mood before they say a word.