chin
Enable an AI agent to recognise a chin, record its form and observable state, and determine which observations or actions are appropriate given uncertainty and consent.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to recognise a chin, record its form and observable state, and determine which observations or actions are appropriate given uncertainty and consent.
The chin is the anterior midline prominence of the human lower face whose osseous core is the mental eminence: a triangular projection at the inferior mandibular symphysis formed by the mental protuberance and paired mental tubercles, clothed by mentalis and a variable soft-tissue pad.
It can be Locate and annotate the chin in a consented image or examination record.; Measure chin dimensions and projection using declared landmarks and calibrated views.; Compare observations over time under matched posture, expression and imaging conditions.; Record local surface changes and reported symptoms for review without assigning an unsupported cause.; Determine whether visibility, consent and available expertise support a proposed observation, contact or modification.; Link chin observations to neighbouring jaw, lip or clinical models when the decision exceeds this model's scope..
Distinguishing features
Locate the candidate region below the lower lip at the anterior lower face; a region primarily beneath the jaw requires a separate submental boundary decision.
Distinguish the central anterior chin contour from the lateral jawline and jaw angles using declared landmarks.
Distinguish the visible chin surface from underlying mandibular support; an external image alone does not establish bone shape.
Distinguish chin skin from the lower lip using the lip margin and any visible intervening contour transition.
Establish that the referent is an anatomical region rather than a beard outline, protective chin cup or depicted chin.
Scope
+ Identification and boundaries of the chin within the lower face
+ Chin projection, width, height, contour and symmetry
+ Local skin appearance, surface features and reported sensation
+ Changes in chin appearance during lip and jaw movement
+ Chin-specific observation history and constraints on contact or modification
- The mandible as a complete bone and its internal anatomy
- Teeth, bite alignment and dental treatment
- The lower lip and oral cavity as independently modelled regions
- The neck and submental region beyond the declared chin boundary
- Whole-person identity, ancestry or personality inference
- Diagnosis and treatment planning for facial conditions
Characteristics
- Referent and host
- Host individual or specimen; anatomical region, depiction or representation Keeps observations attached to the intended chin and distinguishes direct examination from representation.
- Boundary convention
- Named landmark convention or explicitly annotated region; unresolved Makes measurements and local observations comparable without silently including lip, jawline or neck.
- Anterior projection
- Millimetres relative to a declared reference plane, or calibrated image ratio; unknown Records profile prominence while preserving the reference on which the measurement depends.
- Width and vertical extent
- Millimetres between declared landmarks, or calibrated image ratios Describes chin proportions without relying on subjective size labels.
- Contour and local indentation
- Annotated outline; rounded, angular, tapered or other described contour; indentation present, absent or obscured Captures distinguishing visible form, including a cleft or dimple when observed.
- Midline alignment
- Millimetres or degrees from a declared facial reference; posture recorded Allows apparent asymmetry to be assessed against head position and measurement uncertainty.
- Surface visibility
- Visible, partly obscured or unobservable; obstruction identified Prevents hair, clothing, dressings or image limitations from being treated as anatomical evidence.
- Local surface condition
- Located observations of intactness, colour, texture, swelling or marks; unknown Supports comparison over time while separating visible changes from their possible causes.
- Reported local sensation
- Reported pain, tenderness, altered sensation, no symptoms reported or not assessed; time and location Preserves information unavailable from appearance alone without converting a report into a diagnosis.
- Movement-dependent appearance
- Observed contour or texture change linked to a specified lip or jaw position Distinguishes resting morphology from temporary changes associated with movement.
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 32 questions.
Chin identity and boundaries Establishes which anatomical region is being called the chin and where its ownership ends.
Chin observations become ambiguous when the visible surface, underlying bone and adjacent under-jaw region are treated as interchangeable.
Anatomical referent
Connects the chin to its host and the evidence through which it is observed.
Identified chin region
Record the host and evidence supporting identification of the candidate region as a chin.
- Does this record concern a living individual's chin, a specimen or a representation of one? definition
- Which image, examination or annotation establishes the candidate region below the lower lip? provenance
Regional extent
Makes the transitions to the lower lip, lateral jawline and submental region explicit.
Declared chin boundary
Record the landmarks or annotation defining the chin for this use.
- Which landmarks define the superior, inferior and lateral limits of the recorded chin? boundary
- Are observations beneath the anterior jaw assigned to this chin or to a neighbouring submental model? boundary
Chin form and proportions Records chin geometry in frontal and profile views with explicit reference conditions.
Projection, width and contour help distinguish chins, but comparisons depend on landmarks, scale and posture.
Profile projection
Describes the anterior extent and vertical profile of the chin.
Referenced profile measurement
Record projection and vertical extent without inferring underlying bone shape from the surface.
- Relative to which reference plane and surface landmark is chin projection measured? measurement
- What are the measured vertical extent, scale calibration and head position? measurement
- Does the evidence describe the external contour, underlying support or both? boundary
Frontal contour
Describes transverse extent, alignment and local contour features.
Width, symmetry and indentation
Record frontal geometry and any visible cleft or dimple with uncertainty about obscured regions.
- What chin width and midline offset are measurable using the declared landmarks? measurement
- Is a local cleft or dimple visible, and does it persist across views and expressions? measurement
- Which apparent contour features could result from hair, shadow or head rotation? provenance
Chin surface and local state Separates visible chin surface observations from reported sensations and unknown causes.
A recognisable contour does not establish whether the chin surface is fully observable or whether its local state has changed.
Surface observation
Records what can actually be seen on the chin and what obstructs inspection.
Visible skin and covering
Locate surface features while distinguishing skin from hair, cosmetics, dressings and other coverings.
- Which portions of chin skin are visible, and which are obscured by beard hair or other coverings? measurement
- Where are changes in colour, texture, intactness or apparent swelling observed? measurement
Reported state and change
Connects local reports and changes to their source and timing.
Chin symptoms and baseline
Record reported sensation and departures from a documented baseline without assigning a cause.
- What pain, tenderness or altered sensation is reported specifically within the chin boundary, and by whom? provenance
- When was the change first noticed, and what earlier observation supports the comparison? provenance
- Does the intended decision require referral to a clinical model or qualified reviewer? action
Chin movement and support Records how chin appearance relates to lip and jaw position and distinguishes surface evidence from evidence of support.
A single expression can change the apparent chin contour, while visible form alone leaves underlying contributions unresolved.
Expression-dependent form
Links visible chin changes to observed facial movement.
Rest and movement comparison
Compare chin contour and skin texture across recorded lip and jaw positions.
- What lip position, jaw position and expression accompany each chin observation? provenance
- Which contour changes, dimpling or creases appear during movement and resolve at rest? measurement
Surface and support distinction
Keeps external morphology separate from claims about bone or other underlying structures.
Supported anatomical attribution
Record what evidence, if any, supports attributing chin form to an underlying structure.
- What evidence beyond external appearance is available about underlying chin support? provenance
- Which questions about bone, teeth or bite must be owned by the mandibular or dental model? boundary
Chin observation and action Defines conditions for useful chin observations and the limits of authorised contact or modification.
Measuring, touching, grooming or modifying a chin requires different evidence and permissions, particularly when the surface is obscured or changed.
Comparable observation
Establishes whether images or measurements can support the intended chin comparison.
Chin capture adequacy
Record whether view, scale, lighting and visibility are sufficient for the requested assessment.
- Are frontal and profile views sufficient to distinguish chin contour from perspective and shadow? measurement
- What additional consented observation would resolve the specific uncertainty about chin form or surface state? action
Contact and modification limits
Connects proposed chin actions to consent, local observations and the responsible specialist model.
Chin action eligibility
Record the intended action, its authorised extent and unresolved prerequisites.
- Is the proposed action imaging, measurement, contact, grooming or anatomical modification, and what consent covers it? action
- What observed chin condition or reported symptom requires review before the proposed contact or modification? action
- Which clinical, grooming or equipment model owns the procedure and its suitability criteria? boundary
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- osseous mental eminence (mental protuberance plus mental tubercles)
- soft-tissue chin pad (mentum overlying mentalis)
- cleft or dimpled chin (midline sulcus of the pad or tubercles)
- deficient or receding chin (microgenia)
- hyperplastic or prominent chin (macrogenia)
- square versus rounded chin contour (sexed morphology used in planning)
- asymmetric chin (laterognathia or unilateral hypertrophy)
- osteotomized or reconstructed chin after genioplasty
- Which of these kinds and varieties hold for the sense of chin this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q8273077 - Item for the mental protuberance, the named bony core of the chin; a separate mentum item was not confirmed in this pass.
- Foundational Model of Anatomy - 59430 - FMA class Mental protuberance
- Terminologia Anatomica 1998 - A02.1.15.005 - Latin protuberantia mentalis
- Terminologia Anatomica 2 / TAH - TA2 840; TAH:U730 - Official English term: mental protuberance of mandible
- Which of these identifiers and schemes hold for the sense of chin this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Terminologia Anatomica 1998 (FCAT/IFAA) - protuberantia mentalis, A02.1.15.005
- Terminologia Anatomica Humana / TA2 (IFAA) - mental protuberance of mandible, TA2 840, TAH:U730
- Foundational Model of Anatomy (University of Washington) - FMA 59430
- Which of these standards and regulation hold for the sense of chin this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Palpable midline landmark on the mandibular body for dental, oral and maxillofacial work.
- Lateral cephalometry and surgical planning: pogonion (most anterior) and menton (most inferior) locate chin projection and height for genioplasty and orthognathic surgery.
- Osseous genioplasty and chin contouring, including feminizing reduction of height and squareness.
- Palaeoanthropology and comparative anatomy: the projecting mental eminence is treated as a derived Homo sapiens mandibular trait.
- Population description of cleft versus smooth chin as a continuous external trait, not a Mendelian teaching example.
- Which of these real-world use hold for the sense of chin this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- soft-tissue anterior mandibular height (stomion inferius to soft-tissue menton) - females 40 ± 2; males 44 ± 2 - mm
- bony vertical chin height (mandibular incisal edge to menton; Riolo norms as used in genioplasty) - females about 42; males about 49 - mm
- lower-face height (anterior nasal spine to menton) - about 63 ± 5.5 (Caucasian norms) versus 66 ± 4.5 (Asian norms) in one surgical series - mm
- chin-throat length (submental neck point to soft-tissue menton) - 42 ± 6 - mm
- CT chin height (B-point to menton) and local projection (pogonion to that height line) - height about 13-29 (means near 21-22); projection about 3-7 in one adult CT sample - mm
- labiomental sulcus depth (inferior lip margin to pogonion vertical) - about 4 - mm
- mentocervical angle (glabella-pogonion to gnathion-cervical point) - 80-95 - degree
- Which of these typical measurements hold for the sense of chin this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Mental-nerve injury during anterior mandibular osteotomy, with numbness of the chin pad and lower lip.
- Age-related resorption of the anterior mandible and ptosis of the chin soft tissues.
- Over- or under-projection of pogonion after osseous genioplasty.
- Macrogenia diagnosed when the deformity is mandibular position or rotation rather than local chin hyperplasia.
- Cleft chin counselled as a single-gene dominant; pedigree and population data show a continuous, sex- and age-influenced trait.
- Which of these failure modes and hazards hold for the sense of chin this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Cleft-chin frequency ranged from 4% to 71% across Indian samples; Günther recorded 9.6% in German men and 4.5% in German women.
- Surgical cephalometric norms differ: ANS-Me (and related lower-face length) is longer in the Korean/Asian figures cited for genioplasty than in German/Caucasian figures.
- In one African American and Caucasian skull series, males had larger absolute chin height; male chins read as square and female as round across both groups, so feminizing genioplasty is mainly contour, not routine width reduction.
- Descriptive names are not stable: mental protuberance, mental eminence, mental osseum, tuber symphyseos and mental trigon are used for overlapping but not identical osteological units.
- Which of these regional variation hold for the sense of chin this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- mental spines (genial tubercles) - Lie on the lingual surface of the symphysis as genioglossus and geniohyoid attachments; the chin is the labial midline prominence.
- mental foramen and mental nerve - The foramen opens on the buccal body, typically below the premolars, as a neurovascular portal; it is lateral to, not identical with, the chin point.
- mandibular symphysis - The fused midline of the two halves of the mandible; the chin is only the anterior-inferior eminence of that region.
- lower lip - Separated from the chin pad by the labiomental sulcus; the lip is vermilion and orbicularis oris, not the mentalis pad over bone.
- pogonion, menton and gnathion - Three cephalometric points on the chin region: pogonion most anterior, menton most inferior, gnathion anteroinferior; none is the whole chin.
- mandibular prognathism - Forward position of the whole jaw (e.g. ANB) versus local projection of the mental eminence (pogonion relative to B-point or the NB line).
- Which of these neighbouring kinds and how to tell them apart hold for the sense of chin this model covers, and on what evidence? provenance
Sources
- Mental protuberance - Gray-derived description of the triangular mental protuberance and paired mental tubercles as the bony basis of chin shape; TA98, TA2 and FMA identifiers.
- mental protuberance 730 (Terminologia Anatomica Humana unit) - Official IFAA term 'mental protuberance of mandible', Latin protuberantia mentalis mandibulae, TAH:U730, and the taxonomic definition as a midline prominence on the anterior mandibular body.
- Mental protuberance (Q8273077) - Wikidata item for the bony eminence, with FMA 59430, TA2 840 and TA98 A02.1.15.005.
- The human chin revisited: what is it and who has it? - Anthropological distinction of mental protuberance, mental tubercles, mental fossae and mental trigon, and that basal protrusion is the primary criterion used to identify a chin.
- Mental Eminence in the Historical, Surgical and Anthropological Perspective: A Scoping Review - Treats the human chin as mental eminence: protuberance, tubercles and ossified mandibular symphysis as one applied anatomical unit.
- Myths of Human Genetics: Cleft Chin - Cleft versus smooth chin as a continuous trait with wide population and sex differences, not a single-gene dominant.
- 22 Genioplasty - Clinical use of pogonion and ANS-Me in chin assessment; Asian versus Caucasian lower-face height norms.
- Mandibular skeletal orthognathic surgery - Soft-tissue chin height, chin-throat length and labiomental-fold proportions used in surgical facial analysis.
- Osseous genioplasty in conjunction with bimaxillary orthognathic surgery: a review of 262 consecutive cases - Pogonion-to-NB as the operative measure of chin projection; Riolo vertical chin-height means of 42 mm (female) and 49 mm (male).
What the second pass must settle
- Does the registry intend chin to cover only human anatomy, or also comparable regions in other species and represented figures?
- Which anatomical boundary convention should govern the transition between chin, lower lip, lateral jawline and submental region?
- Which landmark and capture protocols provide sufficiently repeatable chin measurements for the intended agent decisions?
- Should underlying bony chin anatomy be owned here or exclusively linked from a mandible model?
- Which researched criteria and specialist models should govern escalation of local changes and suitability for chin contact or modification?