Premolars Revision - Dentition

Lecturer

Oral biology department

BY

Dr. Rehab Ali

Maxillary first premolar

It has 5 aspects:

Buccal Lingual Mesial Distal

occlusal

Maxillary second premolar

It has 5 aspects:

Buccal Lingual MesialDistal

occlusal

Beginning of calc.

(month)

Crown completed

EruptionRoot completed

4

45

53

3

1.5-2y

11-12

2-2.5y

10-11

94-5m 11

10-12

10-12 +3 ye

ars

-5 ye

ars

Geometric outline of the crown

• Facial and lingual aspects have trapezoidal 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 blunt

Longer M slope than D Shorter M slope than D

Mesial contact area in the M1/3 while distally more occlusal.

Mesial contact area at the jun. of O and M1/3 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

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 (0.5 mm shorter)

80%, 2 roots

L root is shorter than B root.

Rare to have 2 roots(20%)In case of two roots the L root is shorter.

4 5

Do you like to be a real dentist

or…..?

Geometric outline of the proximal aspect

Trapezoidal in shape

Smallest uneven sides occlusaly

Mesial aspectDistal aspect

Mesial aspect

B cusp is longer than L cusp by 1mm

4

The cusps are nearly at the same level.

The occlusal table is wide.

5

Mesial DG and canine fossa.

The crown surface is smooth and convex while root has shallow developmental depression.

The occlusal table is wide,but narrower than 4.

Root trunk about half the root length.

4 5

Contact area:

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

At the jun. of O and M 1/3 (OC dimension) and slightly buccal to midline (BL dimension)

Mesial aspect

MMR at the M1/3 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.

CA cervically positioned and more buccally than MCA.

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.

I hope you are better now,

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 found.

M and D fossae.

Not found. Supplemental grooves could be found (wrinkled)

Pulp cavity.

MD section BL section

Pulp chamberNarrow Wide

Root canals

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

L canal is larger &more accessible

In 5 one centralized large canal is present, but may two canals could be exist.

Mandibular first premolar

Buccal Lingual Mesial

occlusal

It has 5 aspects:

Distal

Mandibular second premolar

Buccal Lingual Mesial

occlusal

It has 5 aspects:

Distal

Geometric outline of the crown

• Facial and lingual aspects have somewhat wider trapezoidal shape due to wider cervical third than 4.

54

Facial Outlines and surface anatomy

B cusp

pointed and long

Well prominent B ridge Less prominent B ridge

B cusp

short and less pointed

Lingual outline and surface anatomy

54

The lingual surface is convex with maximum convexity 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 convex with maximum convexity at O1/3.

No MLDG

5Three cusp type:

ML cusp is longer and larger than DL cusp. They both shorter than B

cusp and less pointed .

DM

The surface convex with maximum convixty at O1/3.

The L developmental groove between the 2 cusps

N.B. Very little or no lingual convergancy.

Proximal outlines

54

Lingual inclination well prominent

Lingual inclination less prominent

Rhomboidal in shape with narrow occlusal table.

54

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 oblique while distally is straight

.

ML developmental groove present at the junction of L

and M surfaces .

Proximal surface anatomy

Mesial aspectDistal aspect

Contact area is broader, MCA is directly situated cervically and lingually below the B cusp

positioned.

Contact area nearly at same level

Three cusp type:

ML cusp is longer and larger than DL cusp .

DL cusp is shorter and smaller than ML cusp .

Mesial aspect Distal aspect

Both lingual cusps are shorter than the buccal cusp and less pointed

Surface anatomy is simillar to that of 4

Geometric outline of the occlusal aspect

54Two cusp type:

It’s diamond-shaped.

Lingual convergence is sharp.

The outline is oval

Slight lingual convergence

Three cusp type:

The outline is square

Surface anatomy of occlusal aspect:

Elevations:

B triangular ridge.

L triangular ridge.

M & D marginal ridges

Transverse ridge

54

Depressions:

Central developmental groove

Mesiolingual developmental groove

54

Central developmental groove

)H or U shaped(.

M and D triangular fossae.

)both r circular,but D is deeper(

M and D triangular fossae (M fossa is oval while D fossa is circular,larger & deeper) snake eyes

Elevations:B triangular ridge.

L triangular ridges (ML &DL) .

M & D marginal ridges

Depressions:

Developmental groove (Y shape formed of MB,DB & L grooves).

M and D triangular fossae.

Central fossa with central pit.

Remember the supplemental grooves!!!

Three cusp type: