بسم هللا الرحمن الرحيمIN THE NAME OF ALLAH THE MOST

GRACIOUS THE MOST MERCIFUL

Mandibular 2nd premolarBy:

Prof Dr Mohamad HelalHead of oral Biology Department

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THE PREMOLARS

Premolars There are four maxillary and four mandibularpremolars.

4&4 contact:

3 & 3 mesially and

5 & 5 distally

5 & 5 contact:

4 & 4 mesially and

6 & 6 distally.

Relations:

General Features of Premolars

• They are transitional teeth located between the canine and molar teeth.

• By definition: Premolars are permanent teeth distal to the canines, and successors to deciduous molars.

• There are two premolars per quadrant and are identified as first and second premolars.

• They have usually two cusps(bicuspid) :

One large buccal cusp,

Smaller lingual cusp

• The lower second premolar may-sometimes- have two lingual cusps.

General Features of Premolars

• Generally:

1.The Mandibular 2nd premolar has a larger

crown and longer root than lower one.

2.The1st premolar like the canine while 2nd

premolar like small molar from the occlusal

3.They are similar shape from buccal surfaces

Chronology:

• First evidence of calcifi. 2 ¼ -2 ½ y

• Enamel completed 6-7 y

• Eruption 11-12y

• Root completed 13-14y

Buccal aspect:

• Like buccal surface of lower 1st premolar?

• Trapezoidal shorter cervically

• Mesial outline: slightly concave

• Distal outline: slightly concave

• Contact areas: broad and wide contact located at the same level occlusal to midway cervico-occlusally, the mesial one is more cevically.

• Cusp: shorter and broader than 1st one with mesial inclined plane longer then distal one.

Lingual aspect Buccal aspect

Lingual aspect:

• Two type:

A-Square type (three cusps)

-Two lingual cusps with lingual groove

B-Round type ( two cusps)

- One cusp ligually

Three cusp typeTwo cusp type

• 2nd 1st

Buccal surfaces

Mesialaspect:difference between 1st and 2nd

premolars

Distal aspect

Occlusal aspect

•

• 2 3

Geometric outline of the crownFacial and lingual aspects have

trapezoid shape

But wider

cervically

than 4.

Comparison BetweenMandibular First and Second Premolars

Facial Outlines and surface anatomy

Crown is smaller & B cusp is longer & pointed

Prominent B ridge Less prominent B ridge

Crown is larger & B cusp is shorter and less pointed

Root: Shorter, narrower with pointed apex

Root: longer, broader, with blunt apex

Mandibular First Premolar Mandibular Second Premolar

Lingual outline and surface anatomy

The lingual surface is convex with maximum convexity in middle 1/3(center of crown)

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 convexity in Occ.1/3.

No MLDG

Mandibular First Premolar Mandibular Second Premolar

Ling. s. not sonarrow as in 1st

premolar

MD D M

Three 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 convexity at occ.1/3.

The L developmental groove between the 2 ling. cusps

No ling. convergency.

Proximal outlines

Rhomboid in shape with narrow occlusal table.

Prominent lingual inclination

Rhomboid in shape with wider to some extent occlusal table. Lingual inclination less prominent

Mandibular First Premolar Mandibular Second Premolar

The crown is wider BLThe crown is narrower BL

Maximum convexity at M1/3 Maximum convexity at O 1/3

B cusp tip on line buccal to the root axis.

The mesial and distal marginal ridges are straight

L cusp is shorter and smaller than B cusp but larger than that 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

Mandibular First Premolar Mandibular Second Premolar

The root is wider BL

Three Cusp Type of

MandibularSecond

Premolar

ML cusp is shorter than the B cusp & longer and larger than DL cusp.

DL cusp is shorter and smaller than ML cusp. Both are seen from this aspect.

Both lingual cusps are shorter than the buccal cuspand less pointed

Mesial Aspect

Distal Aspect

Develop.depression

Cerv. line: slightly curved. Cerv. line: nearly straight.

Occlusal Aspect

Two cusp type

Diamond-shaped.

Lingual convergence is sharp.

The outline is round

Slight lingual convergence

Three cusp type

The outline is square

Mandibular First Premolar Mandibular Second Premolar

U- shaped H - shaped

M D

The 3 cusps arewell developed

M D

Surface Anatomy of Occlusal Aspect:

Elevations:

B & L triang. ridges form a transv. ridge.

M & D marginal ridges

Lower 5

Two cusp type

Lower 4

Depressions:

Shallow central devel. groove

M(oval) and D(round) fossae.

Mesiolingual devel. gr.

Central devel. groove extending MD across the occ. surface, over the transv. ridge.

M and D fossae: Circular.

The D fossa is larger than

the M one

Lower 5

Two cusp type

Lower 4

. .

M DM D

Type

Elevations & Depressions

Each cusp has triang. ridge that converge toward a central fossa, which has cent. pit.

M & D marginal ridges are well marked.

No central devel. gr. or transv. ridge

Three cusp type Lower 5

Three devel. gr.(M,D, & L) radiatefrom the cent. Pit : Y-shaped.

The D triang. fossa is smaller than the M one.

M D

Type

MANDIBULARSECOND PREMOLAR

3 cusp type

2 cusp type

PULP CAVITYMD BL

Cross sec. at the cerv. lineround or oval

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