2nd Premolars Lower
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Transcript of 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 .
54
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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