GEOMETRIC CONFIGERATION OF CROWN OUTLINE

Crown Surfaces of teeth(except incisal & occlusal)

triangular trapezoid rhomboid

Facial & Lingual Aspects of all Teeth:

Significance of trapezoid shape of facial and lingual surfaces of crowns

Create interproximal spaces to accommodate interproximal tissue

Provide contact between teeth to protect gingival tissue

Each tooth contacts two teeth in the opposing arch prevention of elongation if a tooth is extracted

Mesial & Distal Aspects of Anterior teeth

Wide basecervically

Strength to the crown

Pointed apexincisally

Biting ,incising &tearing

Penetration through food material

Mesial & Distal Aspects ofMaxillary Posterior Teeth

Wide basecervically

Reduce forces on root

Constricted occlusally

Easily forced into food

Helps self cleansing of the teeth

trapezoid

Mesial & Distal Aspects of Mandibular Posterior Teeth

Lingual inclination

Properocclusion

Axis of crowns and roots of

teeth in both jaws

Parallel toeach other

rhomboid

Prevent clashing of cusps during function

Geometric outline of the proximal aspect

Upper premolars

Trapezoid in shape

Smallest of the uneven sides:

occlusaly

4 5

Lower premolars

45

Rhomboid With

narrow occlusal table .

Lingual inclination more prominent in

4 than 5

The Arrangement of The Arrangement of TeethTeeth

Dental arches conform to

curved planes

Dental Arch Dental Arch FormForm

Anatomical Arrangement of Teeth

“ “Parabolic CurveParabolic Curve””

Anterior segment: semicircular

Middle segment: straight

Posterior segment: straight // to mid line

Segments of the parabolic curve:

•Overlap at the canines and first molarOverlap at the canines and first molar ( which serve as anchor support )( which serve as anchor support )•Anterior segment of mandibular archAnterior segment of mandibular arch smaller than that of maxillary.smaller than that of maxillary.• Middle segment of mandibular archMiddle segment of mandibular arch extends distally to DB cusp of 1extends distally to DB cusp of 1stst molar molar•Posterior segment of maxillary archPosterior segment of maxillary arch may incline palatally.may incline palatally.

Maxillary arch is larger than mandibular:• Allows extension of mandibular movements• Prevent lip and cheek biting• Prevent clashing of thheth during function

The Bonwill TriangleThe Bonwill Triangle::

The mandible adapts

to a 4” equilateral

triangle

Emphasize bilateral

symmetry of mandibular arch

Occlusal Curves of Teeth

Curve of Spee

In sagittal

plane(lateral view)

Curve of Wilson

In coronal Plane

(posterior view)(transverse)

Sphere of MonsonSphere of MonsonMonson formulated the Spherical Theory –

a three dimensional a three dimensional occlusal modelocclusal model

Combining Curve of Spee & curve of Wilson

glabella

Compensating Curvatures ofCompensating Curvatures of Individual TeethIndividual Teeth

The long axes of teeth are not perpendicular to the horizontal plane

Any line bisecting the crown and root of a tooth, when extended , shows axial curvature

These axial arcs have a tendency toward paralellism

Function:stabilize each tooth in the arch Best resistance to masticatory forces Occlusal balance to teethPromotion of mesial drift

Angulation of Individual Teeth in Relation to Various planes

Facial view Mesial view

M-D angulation B-L angulation

Mesio-distalMesio-distal inclinationinclination

andand

Facio-lingualFacio-lingual InclinationInclination

Angulation of Individual Teeth in Relation to Various planes

The axial angulation of teeth relative to:

median plane horizontal plane varies with each

group of teeth

Facial view

•Incisors are placed with their axes at approximately 60 degrees to the horizontal plane; the more posterior the tooth the less acute the angle

Proximal viewProximal view

•Mandibular posterior teeth tip lingually, toward the median plane; the long axes of maxillary posterior teeth are more parallel to the median plane

Mesio-distalMesio-distal inclinationinclination

Facio-lingualFacio-lingual InclinationInclination