04. premolars - dentition

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Cairo University Faculty of Oral and Dental Medicine Prof. Dr. Nahed A. Khalil Head of Oral Biology Department & Contributing Staff Members Human Dentition

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Page 1: 04. Premolars - Dentition

Cairo University

Faculty of Oral and Dental Medicine

Prof. Dr. Nahed A. KhalilHead of Oral Biology Department

& Contributing Staff Members

Human Dentition

Page 2: 04. Premolars - Dentition

premolars

Page 3: 04. Premolars - Dentition

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

Page 4: 04. Premolars - Dentition

Maxillary first premolar

It has 5 surfaces:

Buccal

Lingual Mesial Distal

occlusal

Page 5: 04. Premolars - Dentition

Geometric outline of the crown

Buccal and lingual surfaces have trapezoid outline .The smallest uneven side cervically.

Page 6: 04. Premolars - Dentition

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

Page 7: 04. Premolars - Dentition

.

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.

Page 8: 04. Premolars - Dentition

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.

Page 9: 04. Premolars - Dentition

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.

Page 10: 04. Premolars - Dentition

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.

Page 11: 04. Premolars - Dentition

Geometric outline of the proximal aspect

Trapezoid in shape

Smallest of the uneven sides

is occlusaly

Mesial surface

Distal surface

Page 12: 04. Premolars - Dentition

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

Page 13: 04. Premolars - Dentition

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

Page 14: 04. Premolars - Dentition

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).

Page 15: 04. Premolars - Dentition

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

Page 16: 04. Premolars - Dentition

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.

Page 17: 04. Premolars - Dentition

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

Page 18: 04. Premolars - Dentition

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.

Page 19: 04. Premolars - Dentition

Pulp cavity.MD section BL section

Pulp chamber:

Narrow Wider

Root canals:

2 root canals (B&L)

L canal is larger &more accessible

Page 20: 04. Premolars - Dentition

Maxillary second premolar

It has 5 surfaces:

Buccal

Lingual MesialDistal

occlusal

Page 21: 04. Premolars - Dentition

Geometric outline of the crown

• Buccal and lingual surfaces have trapezoid outline.

The smallest of the uneven sides is cervically.

Page 22: 04. Premolars - Dentition

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.

Page 23: 04. Premolars - Dentition

4 5MD D M

Prominent B ridge Less prominent B ridge

Narrow cervical portion. Wider cervical portion.

Short root. Longer root.

Page 24: 04. Premolars - Dentition

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

Page 25: 04. Premolars - Dentition

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.

Page 26: 04. Premolars - Dentition

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.

Page 27: 04. Premolars - Dentition

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.

Page 28: 04. Premolars - Dentition

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.

Page 29: 04. Premolars - Dentition

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

Page 30: 04. Premolars - Dentition

Long Central DG

M and D triangular fossae.

M developmental groove

54

Shorter Central DG.

Not present.

M and D triangular fossae.

Page 31: 04. Premolars - Dentition
Page 32: 04. Premolars - Dentition

Mandibular first premolar

Buccal

Lingual Mesial

occlusal

It has 5 surfaces:

Distal

Page 33: 04. Premolars - Dentition

Geometric outline of the crown

• Buccal and lingual surfaces have trapezoid outline.

The smallest uneven side is cervically.

Page 34: 04. Premolars - Dentition

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

Page 35: 04. Premolars - Dentition

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.

Page 36: 04. Premolars - Dentition

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.

Page 37: 04. Premolars - Dentition

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.

Page 38: 04. Premolars - Dentition

Geometric outline of the proximal surfaces

Mesial surface

Distal surface

Rhomboid in shape

With narrow occlusal

table

Lingual inclination is well prominent

Page 39: 04. Premolars - Dentition

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

Page 40: 04. Premolars - Dentition

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.

Page 41: 04. Premolars - Dentition

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.

Page 42: 04. Premolars - Dentition

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.

Page 43: 04. Premolars - Dentition

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

Page 44: 04. Premolars - Dentition

GEOMETRIC OUTLINE OF THE OCCLUSAL ASPECT

MDIt’s diamond-shaped.

Lingual convergence is sharp.

Mesial outline is slightly curved.

Distal outline is more convex.

Page 45: 04. Premolars - Dentition

Surface anatomy of occlusal aspect:

Elevations:B triangular ridge.

L triangular ridge.

M & D marginal ridges

Transverse ridge

Page 46: 04. Premolars - Dentition

Depressions:

Central developmental groove

M and D triangular fossae.

Mesiolingual developmental groove

Page 47: 04. Premolars - Dentition

Mandibular second premolar

Buccal

Lingual Mesial

occlusal

It has 5 surfaces:

Distal

Page 48: 04. Premolars - Dentition

Geometric outline of the crown

• Buccal and lingual surfaces have trapezoid shape with the shortest uneven side cervically.

Page 49: 04. Premolars - Dentition

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

Page 50: 04. Premolars - Dentition

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

Page 51: 04. Premolars - Dentition

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

Page 52: 04. Premolars - Dentition

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

Page 53: 04. Premolars - Dentition

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

Page 54: 04. Premolars - Dentition

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

Page 55: 04. Premolars - Dentition

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.

Page 56: 04. Premolars - Dentition

Surface anatomy of occlusal aspect:

Elevations:

Buccal triangular ridge.

Lingual triangular ridge.

M & D marginal ridges

Transverse ridge

54

Page 57: 04. Premolars - Dentition

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.

Page 58: 04. Premolars - Dentition

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):

Page 59: 04. Premolars - Dentition