The chewing works in the boring sense — muscles grow when you load them, and the jaw muscle is no exception. The catch is geometry. You're aiming for a sharper jawline; the muscle you're growing produces a wider lower face — the same look Korean cosmetic clinics treat with botox to undo. Meanwhile the loading pattern looks a lot like teeth grinding to the joint that holds your jaw together, and roughly one in ten adults already deals with jaw-pain problems that get worse under that kind of load. Cheap and easy to start, and mostly the wrong tool for the job you think it's solving.
Press a finger just behind the corner of your jaw, under your earlobe, and clench your back teeth. The slab of muscle that bulges out under your fingertip is the masseter. Like any skeletal muscle, it gets bigger under load — chew hard, daily, for months, and it hypertrophies the same way a climber's forearm flexors do Hannam & McMillan 1994. The mechanism is real. The disagreement is what the bigger muscle actually looks like from the outside.
Now run a finger along your jaw from chin to ear — the line you think of as your jawline. The masseter doesn't live along that line. It sits behind it, at the back corner where the jaw turns up toward the ear. Hypertrophy bulges that corner outward and downward. The sharp chin-to-ear border in every reference photo you've saved is a function of three things this muscle doesn't touch: how much fat sits on top of it, how the bone of the lower jaw is shaped underneath, and how the skin drapes over both. The exercises only move the muscle. They don't change chin projection, they don't reduce fat under the chin, they don't tighten skin. The lever you're pulling and the result you want aren't connected the way the trend assumes.
Does it actually do anything
Yes, in the narrow sense: muscle grows. The cross-sectional ultrasound data is solid Kiliaridis & Kälebo 1991, Raadsheer et al. 1999. The intervention data, on whether you can deliberately train your way there as an adult and have anyone else notice, is almost nothing.
What fills the empty space where the trials should be is a flood of community before-and-after photos. They have three predictable problems. Selection bias: people post the dramatic wins, not the six months of nothing. Confounding: the most-shared transformations almost always overlap with five to fifteen kilos of body-fat loss in the same window, which would sharpen any jawline regardless of what the masseter is doing. Camera bias: head tilt, lighting angle, and lens distance change perceived jawline so much that the same face can look transformed across two photos taken minutes apart. None of that means the muscle didn't grow. It means the photos can't tell you whether the growing muscle did anything anyone wants.
What the trend gets wrong
"The masseter is the jawline muscle." It isn't. The masseter sits at the back angle of the jaw, behind the line you actually see in the mirror. The visible chin-to-ear border is bone and skin draping. There is no single chewing muscle that lives along it.
"Strong chewing burns the fat under my chin." Spot reduction doesn't exist; the body doesn't pull fat from the area you're working. Submental fat tracks total body fat. Five kilos of weight loss does more for a defined jaw than five hundred hours of chewing.
"It'll fix my weak chin or small jaw." The bone is fixed in adults. Chin projection is a genetic feature of the mandible; filler, a chin-advancement procedure called genioplasty, and orthognathic surgery change it. Chewing doesn't.
"More resistance, more results." Muscle growth plateaus past moderate loading. Jaw-joint wear and tooth wear do not. The curve for cosmetic gain flattens; the curve for injury keeps climbing.
How it goes wrong
The common failure isn't "nothing happened." It's the result you didn't want. Three patterns show up over and over in clinical write-ups and community threads.
Square jaw, achieved
The most-common "success" is the user produces a visibly bulkier masseter and discovers the look they were chasing was something else. Korean aesthetic dentistry has an entire sub-specialty built around shrinking this muscle with botulinum toxin injections, because prominent masseters read cosmetically as a heavy, square lower face that patients pay to undo Kim et al. 2005. The medical literature on "masseteric hypertrophy" before the lookmaxxing wave is exclusively about the cosmetic complaint of having it Smyth 1994. The chewing-exercise community is, in anatomical terms, doing what those clinics undo.
Jaw joint trouble
The temporomandibular joint sits just in front of each ear; you can feel it click if you open your mouth wide enough. Chronic overload of the chewing muscles — by chewing devices, isometric clench routines, or background nighttime teeth grinding — is associated with disc displacement, joint clicking, locked jaw, morning headaches over the temples, and a mouth that won't open as wide as it used to Manfredini & Lobbezoo 2010, Lobbezoo et al. 2018. Around one in ten adults already lives with painful jaw-joint problems at baseline Slade et al. 2016, Manfredini et al. 2011; aggressive chewing protocols plausibly push that number up in users who didn't start with symptoms. The signal to stop is early — a click that didn't used to be there, soreness when you first wake up, a headache over the temple that comes on by mid-morning.
Cracked molars and worn-down teeth
Repeated maximum-force loading on the back teeth is the same pattern as bruxism — chronic clenching and grinding — and bruxism is the leading non-cavity cause of fractured molars, accelerated tooth wear, and broken fillings and crowns Lavigne et al. 2008. A cracked back tooth is a crown, sometimes a root canal. A flattened bite from years of accumulated wear takes serious dental work to rebuild.
If you're going to do it anyway
None of this means you can't ever chew gum. Moderate chewing — a regular stick of gum after meals, a wad of mastic gum for thirty minutes while you work — is fine, and nobody's TMJ blew up from a piece of Trident. The problem is the silicone-device-at-maximum-resistance, twice-a-day, push-through-the-soreness regimen the chewing-product market sells. If you're going to use a chewing device, the harm-floor version is conservative and patient.
The honest framing of the cosmetic side: a motivated user doing this for six to twelve months will produce measurable masseter hypertrophy. Whether that hypertrophy reads as "more defined jawline" depends on how much fat is on top of the muscle and how the underlying bone is shaped. The same effort spent on losing a few kilos of body fat is a near-certain visible jawline improvement; the chewing routine isn't.
What actually moves the needle
If a more defined lower face is the goal, the high-yield interventions, in roughly descending order of effect size:
- Lose body fat. The fat under your chin is just fat — it tracks total body fat closely, and a three-to-five-kilo loss visibly sharpens the jaw on most users in under three months. No other single change competes.
- Fix your head posture. Sitting and walking with your head jutting forward stretches the skin under the chin and flattens the angle of the jaw against the neck. A neutral neck position recovers the visible angle in seconds. Costs nothing.
- Resistance training generally. Lower body fat at the same scale weight; sharper facial planes as a side effect.
- Filler at the jaw or chin border. A clinician injects hyaluronic acid along the bone line. Immediate, reversible, lasts about a year. The lookmaxxing crowd quietly uses this one a lot.
- Chin advancement surgery. Genioplasty moves the bone of the chin forward. Permanent, expensive, the right answer for some specific anatomies and wrong for most readers.
The other side of the trade is also worth naming: if you've already over-built the masseter and want it smaller, masseter botulinum toxin is a thirty-minute clinic appointment that visibly slims the gonial angle over six to eight weeks Kim et al. 2005.
Adjacent topics worth a look. Mewing — postural tongue position pressed against the roof of the mouth — is a different mechanism with different claims and its own arguments to litigate. Body composition is the bigger lever for nearly every reader who clicked on this. Bruxism and night guards matter if your existing nighttime clenching is the actual issue making your jaw sore. Cosmetic filler is the fastest visible change in the lower face and gets less attention here than its real-world use deserves.
- — Heavy chewing loads the jaw joint — risky if you're among the one in ten with jaw-joint pain already.
- — Muscle bulk isn't what sharpens a jawline — body fat does far more for facial definition.
- — Loading the jaw muscle this hard looks a lot like grinding to the joint — it can stir up the same trouble.
- — Like mewing, jaw exercises won't chisel your face; they grow muscle at most.
- — If a sharper jaw is the goal, the things that actually move attractiveness are mostly elsewhere — worth a reality check before you commit.
- — Chewing or training mostly one side bulks that masseter unevenly; if you want a wider jaw, work both sides or you'll end up lopsided.
Substance + claimed effects
"Jawline exercises" is the umbrella term for two converging practices that took off on TikTok and the lookmaxxing forums after roughly 2018: chewing devices (Jawliner, Jawzrsize, Rockjaw, and the cheaper mainstay — Falim or mastic gum chewed in multi-piece wads) and isometric jaw routines (mewing-adjacent tongue-to-palate holds, chin-jut holds, masseter clenches against fingers). The shared mechanism claim is masseter hypertrophy via resisted mastication, producing a sharper-looking lower face. Secondary claims, in roughly decreasing order of frequency in community discourse: reduced submental fat, improved nasal breathing, orthotropic remodelling of the maxilla, TMJ pain relief. The substance this entry covers is the chewing-device + isometric routine; the dimensions in scope are facial appearance (the main draw), jaw musculature, TMJ symptoms, dental wear, and occlusion. Mewing proper — postural tongue training — and orthotropic / craniofacial growth modification are adjacent but distinct enough to warrant their own entries.
Evidence by addressing question
mechanism
The masseter is a skeletal muscle; like any skeletal muscle it hypertrophies under load Hannam & McMillan 1994. Cross-sectional ultrasonography in adults shows masseter thickness correlates with bite-force capacity and with short-face / brachyfacial morphology — heavier chewers, by genetics or habit, run thicker masseters and wider gonial angles Kiliaridis & Kälebo 1991, Raadsheer et al. 1999. So the mechanistic case for chewing-induced hypertrophy isn't speculative: chronic loading enlarges the muscle in the same way grip training enlarges the forearm flexors. The aesthetic question is downstream — does the enlarged muscle translate to a more defined jawline contour, or to a wider, more square lower face? Anatomically, the masseter sits over the gonial angle (the back corner of the mandible). Hypertrophy there bulges the angle outward and downward, producing the "square jaw" Korean aesthetic-dentistry literature treats with botulinum toxin reduction Kim et al. 2005. The "sharp jawline" community-image is actually a function of low submental fat plus a defined border of the mandible from chin to angle — masseter bulk affects the angle, not the chin-to-angle border, and on a high-body-fat face contributes nothing visible at all.
Isometric jaw routines (clenching, chin-juts, "tongue presses against palate") load the masseter, temporalis, and medial pterygoid the same way an isometric handgrip loads the forearm. The mechanism stops there — none of these movements remodel bone in adults; the maxilla and mandible are fused at their sutures by the late teens, and the only documented adult bone remodelling under chronic masticatory load is alveolar (the tooth-supporting bone) Hannam & McMillan 1994.
evidence
Trials of masticatory training as an intervention are sparse and old. Ingervall & Bitsanis 1987 ran a small (n=10) pilot of 28 days of intense gum-chewing exercise in long-face children, finding measurable increases in bite force and modest changes in jaw posture; sample tiny, no aesthetic outcomes, intervention age window irrelevant to adults. There is no adequately-powered adult RCT of any chewing device or isometric protocol with a facial-appearance or jaw-muscle-volume endpoint. The literature is dominated by cross-sectional correlations between masseter thickness and facial form Kiliaridis & Kälebo 1991, Raadsheer et al. 1999 and by clinical case-series of pathological masseter hypertrophy presenting as cosmetic complaint Smyth 1994.
Community evidence is loud and asymmetric. Before/after photos on r/jawsurgery and r/mewing show a small minority with visible gonial-angle bulking after 6–12 months of daily chewing-device use. Selection bias is severe (people post wins, not stagnation), camera-angle confound is universal (jawline photos are extremely sensitive to head tilt and lighting), and concurrent confounders dominate — most of the dramatic before/afters also lost 5–15 kg of submental fat over the same window. Practitioner consensus among orthodontists and oral surgeons: skeptical of cosmetic benefit, concerned about TMJ load and tooth wear; the Korean cosmetic-dentistry establishment treats masseter prominence as a problem to reduce, not produce Kim et al. 2005.
protocol
Community protocols cluster around 15–30 minutes daily of resisted chewing (Jawliner at the manufacturer's "level 1" silicone runs ~30 lbs of force per bite, well within physiological masseter capacity; Falim wads of 6–10 pieces deliver progressively more resistance as the gum dehydrates and stiffens), often split into two sessions. Isometric protocols recommend 3 sets of 10–20 second maximum-effort clenches. No published dose-response curve exists for adult masseter hypertrophy from chewing exercise; community-derived ranges (20 minutes/day, 6 days/week, 6+ months to first visible change) are extrapolated from general skeletal-muscle hypertrophy norms.
contraindications
Three populations should not start: anyone with existing temporomandibular disorder (TMD) symptoms — clicking, locking, morning jaw pain, headaches localized over the temples; anyone with documented sleep or awake bruxism (chewing exercises add load to an already-overloaded system) Lobbezoo et al. 2018, Lavigne et al. 2008; anyone with significant existing tooth wear, cracked-tooth syndrome, or recent dental work (crowns, large restorations). Forces generated by aggressive chewing-device use can exceed habitual chewing forces several-fold Raadsheer et al. 1999, and bruxism-pattern loading is the dominant cause of non-carious tooth structural failure and accelerated attrition Lavigne et al. 2008.
misconceptions
"Chewing exercises sharpen the jawline." The masseter doesn't run along the visible jawline border; it sits over the gonial angle at the back. Hypertrophy widens the lower face there, doesn't sharpen the chin-to-angle line. The "sharp jaw" reading is overwhelmingly a function of submental fat, skin laxity, and underlying mandibular projection — none of which chewing changes.
"More force = more results." Skeletal-muscle hypertrophy plateaus; TMJ and dental wear do not. The dose-response for cosmetic effect is flat past moderate loading; the dose-response for injury is monotonic.
"It tones the face by burning submental fat." Spot reduction doesn't exist. Submental fat is not preferentially mobilized by chewing.
"Chewing exercises will fix my recessed chin / small mandible." The mandible's bony anatomy is fixed in adults. Genioplasty, fillers, or orthognathic surgery alter chin projection; chewing does not.
failure-modes
The dominant failure mode is iatrogenic TMD. The temporomandibular joint sits immediately in front of the ear and articulates the mandible's condyle against the temporal bone via a fibrocartilaginous disc; sustained overload — by chewing devices, isometric clenches, or background bruxism — is associated with disc displacement, joint clicking, masticatory muscle myalgia, and limited mouth opening Manfredini & Lobbezoo 2010. Population prevalence of painful TMD in adults is ~5–12% baseline Slade et al. 2016, Manfredini et al. 2011; aggressive chewing-device protocols plausibly push that risk higher in users without prior symptoms. Second failure mode: dental — accelerated occlusal wear, microcrack propagation in molars and premolars, restoration failure Lavigne et al. 2008. Third failure mode: occlusal drift / "bite feels off" — anecdotal, mechanism unclear, but consistent enough across community reports to flag. Fourth: cosmetic over-shoot — the user produces visible masseter bulking that reads as "square jaw" rather than the imagined sharper jawline, then seeks botulinum reduction Kim et al. 2005, Smyth 1994.
alternatives
For a more defined lower face, the high-yield interventions in descending order of effect size: body-fat reduction (submental fat tracks total body fat closely; a 5-kg loss visibly sharpens the jaw on most users); posture (forward head posture and a poorly-trained tongue resting position produce a "double chin" appearance independent of fat); resistance training generally (lowers body fat percentage at a given weight, sharpens facial planes); hyaluronic-acid filler at the chin or jawline border (clinician-administered, immediate, reversible); genioplasty (surgical chin advancement, permanent, expensive). Masseter botulinum toxin is the alternative for users who've over-developed; it's also a low-intervention cosmetic option for users whose square jaw is genetic Kim et al. 2005.
practicalities
Chewing devices: $20–60 one-time (Jawliner, Rockjaw); Falim or mastic gum ~$1–3 per multi-piece session, durable for ~30 minutes before dehydration. Isometric routines are free. Time cost is 15–30 minutes daily; the experiential burden is more about jaw fatigue and post-session soreness than time on clock. No infrastructure required.
stakes / payoff
Not applicable in the loss-aversion sense — this is a discretionary cosmetic practice, not a health intervention with a stakes axis. The "payoff" is also modest and conditional (see evidence + misconceptions above); the entry's job is to set realistic expectations and surface the risks the community downplays.
history
Chewing-gum experiments in long-face / open-bite children trace to the 1980s orthodontic literature Ingervall & Bitsanis 1987. Adult cosmetic adoption is recent: the first commercial silicone chewing devices (Jawzrsize, Jawliner) launched around 2014–2018; lookmaxxing and mewing subcultures on Reddit and TikTok drove the post-2020 wave. The pre-2014 medical literature on masseter hypertrophy is exclusively pathological — "masseteric hypertrophy" as a clinical diagnosis presenting for cosmetic reduction Smyth 1994, Kim et al. 2005 — and reads as the inversion of the modern cosmetic goal.
The credibility range
Optimist case. Chronic mechanical loading reliably hypertrophies skeletal muscle. The masseter is no exception. Cross-sectional data Kiliaridis & Kälebo 1991, Raadsheer et al. 1999 and intervention pilots Ingervall & Bitsanis 1987 establish that masseter mass and bite force are modifiable. A motivated user practising 20–30 minutes daily of progressive chewing-device resistance for 6–12 months will produce measurable masseter hypertrophy; in users with low submental fat and the right underlying mandibular geometry, that hypertrophy reads cosmetically as a more defined gonial angle and squared lower face. Cost is trivial, the practice fits into commute or screen time, and the published downside data (TMD risk in asymptomatic users without bruxism) is genuinely thin. Compared to most lookmaxxing interventions — filler, surgery, anabolic compounds — this is unusually low-stakes.
Skeptic case. The mechanism is real; the cosmetic claim is largely wrong. The masseter sits at the gonial angle, not along the chin-to-angle border that defines the "jawline" in front-facing photographs. Hypertrophy there widens the lower face — the exact outcome the Korean aesthetic-dentistry establishment treats with botulinum toxin to undo Kim et al. 2005, Smyth 1994. The dramatic before/afters that fuel the trend are confounded almost without exception by simultaneous fat loss, lighting/angle differences, and selection bias. No adult RCT shows a facial-appearance benefit. Meanwhile the downside data is non-trivial: ~5–12% adult population baseline for painful TMD Slade et al. 2016, Manfredini et al. 2011, with a known dose-response to parafunctional loading Manfredini & Lobbezoo 2010, Lavigne et al. 2008; and accelerated tooth wear is the most common dental consequence of chronic bruxism-pattern loading, which aggressive chewing-device protocols mechanically resemble.
Author's call. The mechanism is real (masseter hypertrophies under load); the cosmetic payoff is small, mistaken, or counterproductive for most users; the downside is real but probabilistic. Net: don't bother. The reader's lower face will move further toward the look they want from a 5 kg fat loss and better posture than from any chewing regimen, and the chewing regimen carries a TMD/dental tail risk the community discourse systematically underrates. Where there's no risk window — moderate Falim chewing for stress, oral motor variety — the practice is fine. Where it tips into max-effort isometric protocols or aggressive daily silicone-device use, the expected value goes negative. Entry lands at action: know with a clear "this is mostly the wrong tool for the job you think it's solving" frame.
Stakeholder + incentive map
- Commercial. Chewing-device manufacturers (Jawliner, Jawzrsize, Rockjaw) have direct sales incentive; their marketing leans on community before/afters and side-steps TMD risk. Mastic-gum and Falim importers ride the same wave at lower margin. Influencer affiliate codes are common on TikTok.
- Practitioner. General dentists, oral surgeons, and TMD specialists are net skeptical or actively opposed — the chewing-device protocol mechanically resembles the bruxism patterns they treat. The Korean aesthetic-dentistry establishment treats masseter hypertrophy as a cosmetic problem requiring botulinum reduction Kim et al. 2005, which makes the cosmetic goal of jaw exercises read backward from their professional frame.
- Community. Lookmaxxing forums (r/lookmaxxing, r/jawsurgery, parts of r/mewing) treat jaw exercise as a baseline-tier intervention; the cultural code reads it as "self-improvement" rather than cosmetic risk. The mewing subculture overlaps and confounds — "mewing" is postural tongue training, not chewing, but the two get bundled in lay discourse.
- Counter-incentive. Cosmetic clinicians selling filler, genioplasty, and botulinum services have a competing-product incentive but also genuine clinical experience with the downstream consequences.
Population variability
- Underlying facial type. Brachyfacial (short-face) users already have prominent masseters and wide gonial angles; further hypertrophy reads as worsening squareness, not improvement. Dolichofacial (long-face) users with thin masseters have the most room to gain visible bulking, but the published intervention data is from this group as children Ingervall & Bitsanis 1987, not adults.
- Body fat. Submental and buccal fat above ~18% body fat in men / ~25% in women masks any underlying mandibular definition; chewing exercises produce no visible aesthetic change in this population.
- Bruxism status. Sleep and awake bruxism are highly prevalent (8–31% of adults across studies) Lobbezoo et al. 2018. Bruxers are exactly the group at highest risk from added masticatory load.
- Age. Adult masseter hypertrophy is achievable but slower than in adolescents Hannam & McMillan 1994; no skeletal remodelling occurs in adults regardless of effort.
- Sex. Aesthetic goals diverge — square jaws are typically pursued by men and avoided by women. Female users producing visible masseter bulking commonly seek botulinum reduction Kim et al. 2005.
Knowledge gaps
No adequately-powered RCT in adults compares a chewing-device or isometric protocol against control on either a facial-appearance endpoint (3D photogrammetry, lay-rater jawline rating) or a TMD-incidence endpoint. No published dose-response curve for adult masseter hypertrophy under chewing load. No long-term (5+ year) follow-up on dental wear or TMD incidence in chronic chewing-device users. The community has run a large uncontrolled n-of-many experiment for ~8 years now; a properly designed prospective cohort would settle most of the open questions cheaply. Until then the optimist and skeptic cases live side by side and the author's call rests on mechanism plus the asymmetry of the downside.
Narrowing relative to the brief. The brief named five consequences: jaw musculature, facial appearance, TMJ symptoms, dental wear, occlusion. Four are covered end-to-end. Occlusion is touched only briefly — adult bite-shift from chewing exercise is community-reported and not well-characterized in the literature (no published mechanism beyond the bruxism-pattern wear that already lives under dental wear). Flagging the gap rather than padding.
Why action: know and not avoid. The honest call from the dossier is "mostly the wrong tool" — not "actively dangerous for everyone." Moderate chewing-gum use is fine; the harm slope is in the silicone-device, max-resistance, isometric-clench end of the trend. avoid would overclaim. know hands the reader the trade. The protocol section's "if you're going to do it anyway" framing carries the practical risk-floor.
No stakes or payoff section. The substance is cosmetic, discretionary, and the call lands skeptically — a felt-experience forecast either way would either inflate the upside (against the dossier) or feel like fear-mongering on the downside.
Rating difficulties. beauty_cumulative at 2 is a judgement call. The substance does produce measurable masseter hypertrophy over months, which scores 2 ("real but slow contribution") under a generous read. But the hypertrophy widens the lower face — the inverse of the user's typical goal — so calling it a 3 ("meaningful long-term aesthetic improvement") would misrepresent direction of effect. Held at 2 with the directional caveat surfaced in the justification. evidence at 2 (sparse, contested, single small adult-relevant intervention pilot) and controversy at 3 (active practitioner-vs-community disagreement) are tightly coupled — both reflect the same underdetermined literature.
Excluded — likely future entries.
- Mewing — distinct substance (postural tongue position), distinct claims, deserves its own treatment.
- Hyaluronic-acid jaw / chin filler — clinician-administered, immediate, reversible; the most-used real-world lower-face cosmetic intervention and conspicuously under-covered in the catalogue.
- Genioplasty / orthognathic surgery — bone-level interventions; surgical decision territory.
- Bruxism and night guards — overlapping mechanism (max-force masticatory load) but a clinical condition, not a cosmetic practice. Should link in from this entry's failure-modes once it exists.
- Masseter botulinum toxin — the "undo" side of jaw exercises; pairs naturally with this entry.
Citation pool. The dossier leans on cross-sectional masseter-morphology data (Kiliaridis & Kälebo 1991, Raadsheer et al. 1999), TMD epidemiology (Slade et al. 2016, Manfredini et al. 2011, Manfredini & Lobbezoo 2010), bruxism / dental wear (Lavigne et al. 2008, Lobbezoo et al. 2018), and the cosmetic-reduction literature (Kim et al. 2005, Smyth 1994). The intervention gap — no adult RCT for chewing-exercise cosmetic outcomes — is the load-bearing fact; if a properly powered trial appears, the entry's evidence score and the optimist/skeptic balance should be revisited.
Jawline Exercises
Silicone chewing devices (Jawliner, Rockjaw) run $20–60 one-time; Falim or mastic gum a few dollars a session. Trivial spend.
Community protocols cluster around 15–30 minutes daily of resisted chewing or isometric clenches, often split into two sessions, with post-session jaw soreness during the loading phase. Real friction; minor in absolute terms.
Chronic chewing load produces real masseter hypertrophy over 6–12 months (Kiliaridis & Kälebo 1991; Raadsheer et al. 1999), but the muscle sits at the gonial angle, not along the chin-to-angle border most readers picture as 'jawline.' Hypertrophy widens the lower face — the same outcome Korean aesthetic-dentistry treats with botulinum reduction (Kim et al. 2005). Real effect, often miscoded as a win; net cosmetic benefit small and conditional on body fat and underlying anatomy.
No adequately powered adult RCT for any chewing-device or isometric protocol with a facial-appearance endpoint. Mechanism is robust (Hannam & McMillan 1994; Kiliaridis & Kälebo 1991) but the only intervention pilot is a small n=10 study in long-face children (Ingervall & Bitsanis 1987); adult cosmetic outcomes are extrapolated from cross-sectional muscle-morphology correlations and community before/afters with severe selection bias.