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
www.oralbiology.azhar.edu.eg
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