Jaw and chin

Mandibular morphology and chin (mental) anatomy: jaw width, mandibular angle, masseter prominence, chin shape and projection, submental contour. Dimensions are drawn from craniofacial anthropometry (Farkas), facial-aesthetics literature (González-Ulloa, Riedel), and orthognathic-surgery references. Mandibular morphology has substantial population-level variation; East Asian populations average wider bigonial breadth and more prominent masseter musculature than European populations.

Dimensions

• Jaw width (bigonial)

  photo-observable

  ordinal · bigonial_breadth_qualitative

  Width of the lower jaw at the gonial angles (bigonial breadth) relative to the cheekbones (bizygomatic breadth).

  Farkas LG (1994). Anthropometry of the Head and Face, 2nd Edition. Reference: bigonial breadth (go-go) relative to bizygomatic breadth (zy-zy).

  Valid values (3)

  • narrowNarrow (tapered)— Bigonial breadth substantially less than bizygomatic; tapered lower face.
  • balancedBalanced— Bigonial breadth approximately 75-85% of bizygomatic; aesthetic reference range.
  • wideWide— Bigonial breadth approaches or exceeds bizygomatic; squared or wider-than-cheekbones lower face. Common in East Asian populations.

• Mandibular angle (gonial angle)

  photo-observable

  categorical · gonial_angle_qualitative

  Sharpness of the gonial angle.

  Aligned with orthognathic-surgery descriptors of mandibular angle morphology; reference values approximately 120-130° for the angle between the mandibular ramus and body.

  Valid values (3)

  • sharp_angularSharp / angular— Visible 90°-leaning angle at the gonial point; defined jawline. More common in male physiognomy and in East Asian populations.
  • moderateModerate— Standard 120-130° angle; defined but rounded gonial transition.
  • soft_obtuseSoft / obtuse— Smooth, rounded transition with no distinct angle. More common in female physiognomy and with subcutaneous fat coverage.

• Masseter prominence

  partly photo-observable

  ordinal · masseter_prominence_qualitative

  Prominence of the masseter muscle as a visible jaw-region landmark. Hypertrophic masseter is the basis for the 'square jaw' appearance distinct from skeletal jaw width.

  Aligned with descriptors used in masseter-reduction (botulinum toxin / surgical) literature on the East Asian face.

  Valid values (4)

  • flat_minimalFlat / minimal— Masseter not visibly contributing to jaw silhouette.
  • moderateModerate— Masseter visible at clench but not at rest.
  • prominentProminent— Masseter visible as a distinct landmark even at rest; squared lower face.
  • hypertrophicHypertrophic— Pronounced masseter mass; visible bulge at the lower jaw.

• Chin projection (sagittal)

  photo-observable

  ordinal · riedel_pogonion_qualitative

  Anterior projection of the chin (pogonion) in lateral view.

  Riedel RA (1957). An analysis of dentofacial relationships. American Journal of Orthodontics, 43(2). Reference: pogonion-to-vertical-line relationship as the standard for chin projection assessment.

  Valid values (3)

  • retrognathicRetrognathic / recessed— Pogonion sits posterior to the Riedel reference plane; receding chin.
  • balancedBalanced— Pogonion approximately at the Riedel reference plane.
  • prognathicPrognathic / projecting— Pogonion sits anterior to the reference plane; prominent chin.

• Chin shape (frontal)

  photo-observable

  categorical · chin_shape_qualitative

  Shape of the chin in frontal view.

  Aligned with descriptors used in genioplasty literature.

  Valid values (5)

  • pointedPointed— V-shaped chin with narrow apex.
  • roundedRounded— Smooth U-shape; no distinct point or angle.
  • squareSquare— Wide, flat chin with sharp lateral angles.
  • cleftCleft (dimpled)— Visible vertical midline indentation in the chin pad.
  • asymmetricAsymmetric— Notable left-right chin asymmetry.

• Chin height (vertical)

  photo-observable

  ordinal · chin_height_proportional

  Vertical chin height proportional to the lower facial third.

  Farkas LG (1994). Reference: chin height (subnasale to menton) proportional to lower facial third.

  Valid values (3)

  • shortShort— Chin height less than lower facial third reference.
  • balancedBalanced— Chin height within the reference range.
  • longLong— Chin height substantially above reference.

• Submental (under-chin) definition

  photo-observable

  ordinal · ellenbogen_karlin_neck_classification

  Visibility of the chin-to-neck transition; presence of submental fat or laxity ('double chin').

  Ellenbogen R, Karlin JV (1980). Visual criteria for success in restoring the youthful neck. Plastic and Reconstructive Surgery, 66(6): 826-837. The Ellenbogen-Karlin neck-aesthetics criteria include submental contour as a primary dimension.

  Valid values (4)

  • well_definedWell-defined— Crisp transition between chin and neck; no submental fat.
  • softly_definedSoftly defined— Visible chin-neck transition with some submental fullness.
  • moderate_submental_fatModerate submental fullness— Visible submental fat pad obscuring the chin-neck angle.
  • marked_submental_fatMarked submental fullness ('double chin')— Pronounced submental fat creating a second visible chin contour.

• Mandibular contour definition

  photo-observable

  ordinal · jawline_contour_qualitative

  Visibility of the mandibular contour from gonial angle to chin.

  Aligned with the contemporary aesthetic-medicine literature on jawline definition (Sundaram et al., Aesthetic Surgery Journal).

  Valid values (4)

  • highly_definedHighly defined— Clear mandibular silhouette visible from frontal and profile views; no submental fat coverage.
  • definedDefined— Mandibular contour visible but soft.
  • softSoft— Mandibular contour partially obscured by soft-tissue coverage.
  • obscuredObscured— Mandibular contour not discernible; full soft-tissue coverage of the jawline.