geometric.shape.& occlusal curves
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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