04. Premolars - Dentition
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Cairo University
Faculty of Oral and Dental Medicine
Prof. Dr. Nahed A. KhalilHead of Oral Biology Department
& Contributing Staff Members
Human Dentition
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premolars
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PREMOLARS
There are four maxillary and
four mandibular premolars:
Upper 1st premolar: upper 4
Lower 1stpremolar: Lower 4
Upper 2nd premolar: upper 5
Lower 2nd premolar: Lower 5
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Maxillary first premolar
It has 5 surfaces:
Buccal
Lingual Mesial Distal
occlusal
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Geometric outline of the crown
Buccal and lingual surfaces have trapezoid outline .The smallest uneven side cervically.
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Buccal OutlinesMesial outline is nearly concave.
Distal outline is nearly straight.
Mesial cusp slope is nearly straight while the distal cusp slope is slightly convex.
Contact areas:
Mesially is at the middle third while Distally it is occlusally positioned which is an exception from other permanent posterior teeth.
Cervical line: is convex root wise. B cusp pointed and long
MD
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.
Outline and surface anatomy of the root
The surface of the root is convex and smooth
The M and D outline of the root tapers to a pointed apex that is slightly curved distally.
If it has two roots, the lingual root is hidden behind the buccal root as it’s shorter and narrower than the buccal root.
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Surface anatomy of the crown
• The buccal surface is convex with the maximum convexity at the cervical 1/3 .
Elevations:
Depressions:Shallow depressions are present mesial and distal to the B ridge (M&D developmental grooves)
• The middle lobe is prominent buccally forming the BUCCAL ridge.
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Lingual outline and surface anatomy of the crown
The lingual surface is convex with the maximum convexity at the middle 1/3
M and D outlines are convex.
• The lingual cusp is shorter by 1 mm but sharper than the buccal cusp
• The D slope of the lingual cusp is longer than the M slope
M D
Cervical line: is convex root wise.
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Outline and surface anatomy of the root
The surface of the root is convex and smooth
The M and D outlines of the root taper to a pointed apex that is curved distally.
If two roots, the lingual root appears shorter and narrower than the buccal root.
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Geometric outline of the proximal aspect
Trapezoid in shape
Smallest of the uneven sides
is occlusaly
Mesial surface
Distal surface
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Lingual outline is convex with maximum convexity at middle1/3.
Cervical line curves occlusally and decreased distally.
Outlines of proximal aspect
Buccal outline is convex with the maximum convexity at the cervical 1/3.
Mesial surface
Distal surface
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Occlusal outline:
B cusp is longer than L cusp by 1mm.
Wide occlusal table.
B cusp tip is below the center of B root.
L cusp tip is in one line with the lingual outline of the L root
MMRis present at the junction of O 1/3 and M 1/3, while DMR is more occlusal
Mesial aspectDistal aspect
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Proximal surface anatomy
Contact area:
Mesial aspectDistal aspect
At the middle third (OC dimension) and slightly buccal to the midline (BL dimension)
Occlusally positioned and more buccally.
Mesial developmental groove is crossing MMR and located lingual to the contact area.
Smooth and convex surface except for a small flat area cervical to contact area .
Mesial Developmental depression in the crown and continues with that between the roots (canine fossa).
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In case of two roots (80%).
Mesial aspect Distal aspect
Root trunk is about half the root length.
Root trunk is longer as the bifurcation is near the apical 1/3
Surface is smooth and convex except deep developmental depression below bifurcation.
Surface is smooth and convex except shallow DD on the root trunk
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In case of one root.
The B and L outlines tapers to a blunt apex on the center of the crown.
The surface is smooth and convex except for a shallow depression in the center that is deeper mesially than distally.
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GEOMETRIC OUTLINE OF THE OCCLUSAL ASPECT
It is hexagonal in shape
• 2 equal buccal sides (MB, DB)
• M side shorter than D side.
• ML side shorter than DL side.
Thickness is greater than width
The crown is wider buccally than lingually.
MD
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Surface anatomy of occlusal aspect:
Elevations:B triangular ridge.
L triangular ridge.
M & D marginal ridges
Depressions:
Central developmental groove
M and D triangular fossae.
M marginal developmental groove.
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Pulp cavity.MD section BL section
Pulp chamber:
Narrow Wider
Root canals:
2 root canals (B&L)
L canal is larger &more accessible
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Maxillary second premolar
It has 5 surfaces:
Buccal
Lingual MesialDistal
occlusal
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Geometric outline of the crown
• Buccal and lingual surfaces have trapezoid outline.
The smallest of the uneven sides is cervically.
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Facial Outlines and surface anatomy of the crown
4 5
B cusp is long and pointed B cusp is short and less pointed
M slope is longer than D M slope is shorter than D Mesial contact A is in the
M1/3 while distally more occlusal.
Mesial contact A is in O1/3 while distally more cervically.
MD D M
Cervical line curved root wise.
Cervical line less curved.
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4 5MD D M
Prominent B ridge Less prominent B ridge
Narrow cervical portion. Wider cervical portion.
Short root. Longer root.
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Lingual outline and surface anatomy of the crown
The L cusp is shorter by 1 mm than the B cusp. The L and B cusps are
nearly of same height.
80% has 2 roots with L root is shorter than B root and its apex is pointed.
Rare to has 2 rootsIn case of two roots the L root is shorter and its apex is more blunt.
4 5
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Mesial aspect
B cusp is longer than L cusp by 1mm
4
The cusps are nearly at the same level.
The occlusal table is narrow.The occlusal table is wide.
5
Mesial DG and canine fossa.
The crown surface is smooth and convex while the root has shallow developmental depression.
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4 5
Contact area: At the middle third (OC dimension) and slightly buccal to the midline (BL dimension)
At the occlusal third (OC dimension) and slightly buccal to the midline (BL dimension)
MMR at the junction of M1/3 &O1/3
MMR positioned more occlusal.
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Distal aspect4
5
DMR more occlusal than MMR
DMR more cervical than MMR
CA occlusally positioned and more buccally than MCA.Smooth and convex surface except for a small flat area cervical to contact area.
CA cervically positioned and more buccally than MCA.Smooth and convex
surface.
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Root trunk is long as the bifurcation is near apical 1/3
Surface is smooth and convex except shallower DD on the root trunk than mesially.
54
One root and if 2 the bifurcation will be more apically.Surface is smooth and convex except deeper DD in the middle of the root than mesially.
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MD MD
Occlusal aspect54
It’s hexagonal
It’s oval
B & L triangular ridges.
M & D marginal ridges
B & L triangular ridges.Thicker M & D MRs
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Long Central DG
M and D triangular fossae.
M developmental groove
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Shorter Central DG.
Not present.
M and D triangular fossae.
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Mandibular first premolar
Buccal
Lingual Mesial
occlusal
It has 5 surfaces:
Distal
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Geometric outline of the crown
• Buccal and lingual surfaces have trapezoid outline.
The smallest uneven side is cervically.
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Buccal Outlines
Mesial and distal outlines are nearly concave
Mesial and distal cusp slopes are also slightly concave Contact areas:
Mesially at the junction of O and M thirds while Distally it’s cervically positioned.
Cervical line: is convex root wise.
MD
B cusp pointed and long
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Outline and surface anatomy of the root
The surface of the root is convex and smooth
The M and D outline of the root tapers to a pointed apex that is curved distally.
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Surface anatomy of the crown
• The buccal surface is convex with the maximum convexity is at C 1/3 representing cervical ridge.
Elevations:
Depressions:Shallow depressions are present mesial and distal to the B ridge
• The middle lobe is prominent buccally forming BUCCAL ridge.
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Lingual outline and surface anatomy of the crown
M and D outlines are convex with marked lingual convergence .
M DCervical line: is convex root wise.
Elevations: The lingual surface is convex
with the maximum convixty at M 1/3
The L cusp is short and small reaching 2/3 the crown length and has a pointed tip.
Depessions: ML developmental groove at
the ML line angle.
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Geometric outline of the proximal surfaces
Mesial surface
Distal surface
Rhomboid in shape
With narrow occlusal
table
Lingual inclination is well prominent
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Lingual outline is convex with maximum convexity at M1/3
Cervical line curves occlusally and decreased distally
Outlines of proximal surfaces
Buccal outline is convex with the maximum convexity at C 1/3 representing …….
Mesial surface
Distal surface
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Outlines of proximal surfaces.
Mesial surface
Distal surface
Occlusal outline: the two cusps are not in the same level
The B cusp is centered above the root. This is due to the presence of lingual inclination.The L cusp tip is in line with the lingual border of the root.
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Outlines of proximal surfaces
Mesial surface
Distal surface
DMR in 4 is straight and at right angle to the axis of the tooth. DMR is occlusal than MMR (unique characteristic
of this tooth).
MMR is inclined from B to L surface \\ to B cusp ridge.
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M & D surfaces are smooth and convex except area cervical to contact area it’s concave.
ML developmental groove is present at the junction of L and M surfaces.
Contact area
Proximal surface anatomy
Mesial surface
Distal surface
nearly at the same level
it’s broader, cervically and lingually positioned.
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Mesial surface
Distal surface
Outline and surface anatomy of the root
B & L outlines are nearly straight and parallel cervically then taper apically to a blunt apex
The surface is smooth and flat with deep developmental groove
The surface is more convex
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GEOMETRIC OUTLINE OF THE OCCLUSAL ASPECT
MDIt’s diamond-shaped.
Lingual convergence is sharp.
Mesial outline is slightly curved.
Distal outline is more convex.
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Surface anatomy of occlusal aspect:
Elevations:B triangular ridge.
L triangular ridge.
M & D marginal ridges
Transverse ridge
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Depressions:
Central developmental groove
M and D triangular fossae.
Mesiolingual developmental groove
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Mandibular second premolar
Buccal
Lingual Mesial
occlusal
It has 5 surfaces:
Distal
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Geometric outline of the crown
• Buccal and lingual surfaces have trapezoid shape with the shortest uneven side cervically.
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54
Buccal outlines and surface anatomy
B cusp
pointed and longWell developed B ridge
Not well developed B ridge
B cusp
short and less pointed
Pointed apex Blunt apex
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Lingual outline and surface anatomy
54
The lingual surface is convex with maximum convixty at M 1/3
The L cusp is short and small reaching 2/3 the crown length and has a pointed tip.
ML developmental groove at the ML line angle.
Two cusp type
L cusp is shorter and smaller than B cusp but larger than of 4
The surface is convex with maximum convixty at O 1/3.No MLDG
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5Three cusp type:ML cusp is longer and larger than DL cusp.However, both of them are shorter than the B cusp and the ML cusp is less pointed.
DM
The surface is convex with the maximum convixty at O 1/3.
The Lingual developmental groove is between the 2 lingual cusps
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Proximal outlines
54
Rhomboid in shape with
narrow occlusal table.
Lingual inclination well prominent
Rhomboid in shape with
narrow occlusal table.
Lingual inclination less prominent
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5
4
Maximum convexity at M1/3 Maximum convexity at O1/3
B cusp tip on line with junction
of B & M 1/3 of the root.The mesial and distal marginal ridges are straight
L cusp is shorter and smaller than B cusp but larger than of 4
The B cusp centered over the root.
The L cusp is short and small reaching 2/3 the crown length
The mesial MR is oplique while distally is straight
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Three cusp type:
ML cusp is longer and larger than DL cusp.
DL cusp is shorter and smaller than ML cusp.
Mesial surface
Distal surface
Both lingual cusps are shorter than the buccal cusp and the ML cusp is less pointed.
Surface anatomy is simillar to that of 4
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Geometric outline of the occlusal surface
5
4
Two cusp type: It is diamond-shaped.
It has two cusps.
Lingual convergence is sharp.
The outline is ovalSlight lingual convergence Three cusp type:The outline is square
no lingual convergence.
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Surface anatomy of occlusal aspect:
Elevations:
Buccal triangular ridge.
Lingual triangular ridge.
M & D marginal ridges
Transverse ridge
54
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Depressions:
Central developmental groove
M and D triangular fossae.
Mesiolingual developmental groove
54
Central developmental groove
H or U shapped. M and D triangular fossae.
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Elevations:
Buccal triangular ridge.
Lingual triangular ridges (ML &DL).M & D marginal ridgesDepressions:
Central developmental groove Y shape M and D triangular fossae with M and D pits .
Lower 5 (Three cusp type):
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