2nd Premolars Lower

8/12/2019 2nd Premolars Lower

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Description of the mandibular second premolars:

a. Chronology.

b. Geometric outline of the crown in different aspects .c. Outlines & Surface anatomy of the crown in differentaspects.

d. Comparison between the 2 types of the secondmandibular premolars in different surfaces.

e. Comparison between the first & second mandibularpremolars


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Chronology First evidence of calcification

21/4 -21/2 Y

Enamel completed

6-7 Y

Eruption

11-12 Y

Root completed

13-14 Y


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There are 2 types differ mainly fromthe occusal & lingual aspects while

the other surfaces are nearly similar


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Buccal Lingual Mesial occlusal

It has 5 aspects :

Distal

Mandibular second premolar: Two Cusp Type


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Buccal Lingual Mesial occlusalDistal

Occurs most often

Mandibular Second Premolar: Three Cusp Type


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Geometric outline of the crown

Facial and lingual aspects have trapezoid out line .

The smallestuneven sidecervically.


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The mesial outline, The distal outline and Mesial & Distal C. A.are at the same like lower 4 except that

Buccal Outlines and Surface anatomy

Surface Anatomy: like that of lower 4 with less developed B ridgeThe buccal cusp in 3cusp form is broader and less pointed

The root has a blunt root apex

D MMD


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No dg

Two

cusp type

Threecusp type

There are 2types

One Lingcusp

Two Lingcusp

M Ling

D Ling

Lingual Aspect

L cusp is smaller & shorter by

about 1 mm than B cusp butlarger than of Lower 4

*ML cusp is longer and largerthan DL cusp.*They both shorter than B cuspand less pointed.*There is Ling developmentalgroove between the 2 cusps

No ling. convergence .


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Proximal outlines

In all lowerposterior teeth

Rhomboid in shape with narrow occlusal table . Lingual inclination less prominent than that of the lower 4

Geometric outline of the crown

Twocusp type

Threecusp type


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Maximum convexity at C1/3 bucally & M 1/3 Lingually

The buccal cusp is shorter than in lower 4 and more buccal to thecenter of the root. While Ling cusp larger than of lower4

The mesial and distal marginal ridges are straight

L cusp or cusps are shorter and smaller than B cusp

DDM M D

Buccal Outlines and Surface anatomy


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Geometric outline of the occlusal aspect

No Lingual convergence.

Two cusp type : Outline is oval

Slight lingual convergence

Three cusp type:Outline is square


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Surface anatomy of occlusal aspect

Elevations

B triangular ridge .

One or 2 L triangular ridge .

M & D marginal ridges

5


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Depressions

From a central pit

*M dg ends at M traingular fossa

*D dg ends at D traingular fossa*Ling dg between the 2 Lingcusps

They form Y shapeM and D triangular fos sae .

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Central developmental groovein a form of

H or U shape.

M and D triangular fossae .


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Elevations:

B triangular ridge .

L triangular ridges (ML &DL).

M & D marginal ridges

Depressions:

Central developmental groove Y shape made of M,D &L dgs

Central pit

M and D triangular fossae.

Three cusp type:

B the largest, ML & DL smallest 1

3 2


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Comparison

Two cusp type

Diamond-shaped .Lingual

convergence issharp.

The geometric outline is oval

Slight lingual convergence

Three cusp type

square

Mandibular First Premolar Mandibular Second Premolar

U- shaped H - shaped

M D

M D

Elevations&depressions + ML dg

Geometricoutline

Surface Anatomy

Elevations & depressions


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Self-Evaluation Review

1. Compare between the 1 st & 2 nd lower

premolars ( 2 cusp type)2. Compare between the two types from the

occlusal aspect


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Wheelers Dental Anatomy, Physiology and

Occlusion, 8th Ed .ASH and NELSON,W.B.Saunders Company, 2003.

Dental Anatomy: Its Relevance to Dentistry,

Julian BW, Rickne CS.5 th Ed,Williams&

Wilkins, Baltimore, 1997.


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2nd Premolars Lower