Premolars

There are four maxillary and four mandibular premolars.

4 & 4 contact 3 & 3 mesially and 5 & 5 distally

5 & 5 contact 4 &4 mesially and 6 &6 distally.

For easy teeth description We have to speak about : • Function (grinding).• Chronology.• Number of lobes (four lobes 3 buccally and 1 lingually or five lobes 3

buccally and 2 lingually).• Geometric outline of the crown.• Outlines of the crown and root.• Surface anatomy of the crown and root.• Pulp cavity.

•Enamel organ appearance.

•Beginning of calcification.

•Crown completed.

•Eruption.

•Root completed

Chronology:

Maxillary first premolar

It has 5 aspects:

Buccal Lingual Mesial Distal

occlusal

Geometric outline of the crown

The smallest uneven side cervically.

• Facial and lingual aspects have trapezoid out line.

Facial OutlinesMesial and distal outlines are nearly concave

Mesial and distal cusp slopes are also slightly concave

Contact areas:

Mesially at the M third while Distally it’s occlusally positioned which is an exception from other permanent posterior teeth.

B cusp pointed and long

Cervical line: is convex root wise.

MD

.

Outline and surface anatomy of the root

The surface of the root is convex and smooth

The M and D outline of the roots tapered to a pointed apex that curved distally.

If two roots, the buccal root hide the lingual root as it’s shorter and narrower than the buccal root.

Surface anatomy of the crown

•The surface convex with maximum convexity at C 1/3 represent……….

Elevations:

Depressions:Shallow depressions were present mesial and distal to the B ridge

•The middle lobe is prominent buccally forming BUCCAL ridge.

Lingual outline and surface anatomy of the crown

The surface is convex with maximum convixity at the M1/3

M and D outlines are convex

•The L cusp is shorter by 1 mm but sharper than the B cusp

•The D slope of L cusp is longer than M slope

M D

Cervical line: is convex root wise.

Outline and surface anatomy of the root

The surface of the root is convex and smooth

The M and D outline of the roots tapered to a pointed apex that curved distally.

If two roots, the lingual root appears shorter and narrower than the buccal root.

Geometric outline of the proximal aspect

Trapezoid in shape

Smallest uneven sides occlusaly

Mesial aspectDistal aspect

Lingual outline is convex with maximum convexity at M1/3

Cervical line curves occlusally and decreased distally

Outlines of proximal aspect

Buccal outline is convex with maximum convexity at C 1/3 represent …….

Mesial aspectDistal aspect

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 on line with L root

MMR present at the junction of O 1/3 and M 1/3, while DMR more occlusal

Mesial aspectDistal aspect

Proximal surface anatomy

Contact area:

Mesial aspect Distal aspect

At the middle third (OC dimension) and slightly buccal to 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 continue with that on the root (canine fossa).

In case of two roots (61%).

Mesial aspect Distal aspect

Root trunk about half the root length.

Root trunk is longer as bifurcation is near 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

In case of one root.

The B and L outlines tapered to a blunt apex on the center of the crown.

The surface is smooth and convex except shallow depression in the center that is deeper mesially than distally.

Geometric outline of the occlusal aspect

It’s hexagonal

•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. Why?

MD

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 developmental groove

Can you tell

Which tooth, which aspect.

4 , occlusal aspect.

Triangular ridge of B cusp.Triangular ridge of L cusp.

M &D marginal ridges

Central developmental groove

M triangular fossa.

D triangular fossa.

Mesial developmental groove

Pulp cavity.

MD section BL section

Pulp chamber:

Narrow Wider

Root canals:

2 root canals (B&L) but rare 3 canals

L canal is larger &more accessible

Maxillary second premolar

It has 5 aspects:

Buccal Lingual MesialDistal

occlusal

Geometric outline of the crown

• Facial and lingual aspects have trapezoid out line.

The smallest uneven side cervically.

Facial Outlines and surface anatomy of the crown

4 5

B cusp is long and pointed B cusp is short and less pointed

Longer M slope than D Shorter M slope than D

Contact mesial A in the M1/3 while distally more occlusal.

Contact mesial A in O1/3 while distally more cervically.

MD D M

Cervical line curved root wise. Cervical line less curved.

4 5MD D M

Prominent B ridge Less prominent B ridge

Narrow cervical portion. Wider cervical portion.

Short root. Longer root.

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.

61% 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 more blunt.

4 5

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 root has shallow developmental depression.

4 5

Contact area:

At the middle third (OC dimension) and slightly buccal to midline (BL dimension)

At the occlusal third (OC dimension) and slightly buccal to midline (BL dimension)

Mesial aspect

MMR at the junction of M1/3 &O1/3

MMR positioned more occlusal.

Distal aspect

4 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.

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.

Distal aspect

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.

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

Long Central DG

M and D fossae.

M developmental groove

54

Shorter Central DG.

Not present.

M and D fossae.