permanent mandibular molars
TRANSCRIPT
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PERMANENTPERMANENT
MANDIBULAR MOLARS MANDIBULAR MOLARS
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� Largest and strongest teeth
� First , second and third molars
� Functionally similar but vary in form
� 2 roots ± mesial and distal ± sometimes fused
Mand first molar
Mand second molar
Mand third molar
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MD
B
L
Shorter height cervico occlusally
MD measurements of all molars > MD measurements of all Mand anteriors
MD > BL measurement
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� Perform the major work during mastication
because of
» Bulk due to greater dimensions
» Anchorage due to multiple roots and bifurcated root
trunk
Root bifurcation
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Mand molar ± MD > BL
M D
L
B
Max molar ± BL > MD
B
P
M D
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MANDIBULARMANDIBULARFIRST MOLAR FIRST MOLAR
( 36 & 46)( 36 & 46)
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MANDIBULAR FIRST MOLAR
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BASIC MORPHOLOGY
� Largest tooth in the mandibular arch
� Cusps ± 5 cusps
� Buccal cusps ± 2
� Lingual cusps ± 2
� Distal -- 1
M
L
B
D
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� Roots� 2 roots ± mesial root
distal root
Broad buccolingually , widely separated at the apices
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CHRONOLOGYCHRONOLOGY
First evidence of calcification 3 - 4 months
Enamel completion 4 - 5 yrs
Eruption 6 - 7 yrs
Root completion 9 yrs
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MEASUREMENTMEASUREMENT
Cervico incisal length of the crown - 9.5 mm
Length of the root - 12.5 mm
Mesio distal diasmeter of the crown - 5.0 mm
Mesio distal diameter at the cervix - 3.5 mm
Labiolingual diameter of the crown - 6.0 mm
Labiolingual diameter at the cervix - 5.3 mm
Curvature of the cervical line mesial
distal
- 3 mm
- 2 mm
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NOMENCLATURENOMENCLATURE
SYSTEM TOOTH NUMBER
Zsigmondy and Palmer
Universal 19 , 30
FDI system 46 36
Victor and Haderup
6 6
6- 6-
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5 ASPECTS
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BUCCAL ASPECT
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BUCCAL ASPECT OF MANDIBULAR FIRST MOLAR
OUTLINE OF THE CROWN
CUSPS
DEVELOPMENTAL GROOVES
BUCCALSURFACE
ROOTS
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Crown outline
TRAPEZOIDAL IN SHAPE WITH LONGER OCCLUS AL SIDE
MD MESIAL OUTLINE
DISTAL OUTLINE
CERVICAL LINE
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MESIAL OUTLINE :Concave at the cervical third of the crown
Convex mesial contact area
DISTAL OUTLINE:
Straight above the cervical line
Convex distal contact area
CERVICAL LINE:
Regular in outline dipping apically towards
the root bifurcation
Mesiodistally 1.5 ± 2 mm less than
at the contact areas
M
D
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Cusps
Mandibular first molar has 5 cusps
2 buccal cusps, distal cusp and 2 lingual cusps
From the buccal aspect-
2 buccal cusps
Buccal portion of distal cusp
Tips of 2 lingual cusps
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Cusps
Size of the cusps:
Mesiobuccal cusp - widest mesiodistally, less curvature of the cusp ridges,
Distobuccal cusp - as wide as MB cusp, greater curvature of the cusp ridges
Distal cusp - smallest of all the cusps and more pointed
Buccal cusps are worn considerably to become flat
showing the buccal cusp ridges at the same level
WHY?
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Developmental grooves
2 grooves buccally
Mesiobuccal DG
Distobuccal DG
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Developmental grooves
Mesiobuccal developmental groove
Line of demarcation between mesiobuccal
and Distobuccal lobe
Shorter of the two grooves
Little mesial to the root bifurcation
Terminus centrally located cervico occlusally
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Developmental grooves
Distobuccal developmental groove
Line of demarcation between Distal lobe and
Distobuccal lobe
Longer of the two grooves
Travels with the axis of the distal root
Terminus at the cervical third of the crown
near the distobuccal line angle
DBLA
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Buccal surface of first molar
� Convex and smooth
� 2 developmental grooves between the cusps
� Developmental depression at the middle third
of the buccal surface (mesiodistally)
� Cervical ridge at the cervical third of the crown
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Roots
� Mesial root
� Distal root
� Root trunk
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Roots
Mesial root
From cervical to middle third ± mesial curvature
From middle third to apical third ± distal curvature
Tapered apex directly below the Mesio buccal cusp
Crest of curvature - mesial to the crown cervix
MD
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Distal root
Axis in a distal direction from cervix to the apex
Less curved than the mesial root
Pointed apex, curved mesially or distally,
below or distal to the DCA of the crown
Roots
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Roots
Root bifurcation
Located 3mm below the cervical line
Deep developmental depression
progressing cervically
No developmental grooves
3mm
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I beam principle
From the buccal aspect,
� 2 roots ± mesial and distal ± wider mesiodistally
� Developmental depressions are present on mesial and distal sides ±
reduces the mesiodistal diameter of the roots at these areas
� Roots are thicker at the lingual borders
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I beam principle
MD Buccal
Cross section at the furcation level of the root
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LINGUAL ASPECT
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LINGUAL ASPECT OF MANDIBULAR FIRST MOLAR
CROWN OUTLINES
CUSPS
DEVELOPMENTAL GROOVES
LINGUALSURFACE
ROOTS
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Crown outline
� Mesial outline
� Distal outline
� Cervical line
MD
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� Mesial outline
Convex from the cervical line to the MMR
Crest of contour is at a higher level (MCA)
� Distal outline
Straight above the cervical line
Convex DCA( distal surface of the distal cusp)
Junction of DL cusp with the DMR is sharp
- sometimes groove present at this junction
Crown outline
MD
MMRDMR
Disto lingual cusp
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Crown outline
� Cervical line
Irregular
Points sharply towards the
root bifurcation
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Cusps
cusps seen - 2 lingual cusps & Lingual potion of distal cusp
� Lingual cusps
Pointed high cusp ridges
ML higher than , Width ML = DL
Cusp ridges form obtuse angles
(100 degrees) at the cuspal tips
� Distal Cusp
Lower level than the
mesiolingual cusp
M
D
ML
DLDistal
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Grooves
Lingual developmental groove
Line of demarcation between two lingual cusps
Travels for a short distance only
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Lingual surface
� Smooth and spheroidal on the lingual lobes
� Concave at the groove area
� Flat at the cervical region
Part of mesial and distal surfaces are seen due to
lingual convergenc e of the c r ow n mesi od ist ally
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Roots
Mesial and distal roots
Measure 1mm longer than the buccal aspect
Why?
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Roots
Cusp ridges and the cervical line are placed at a higher level than on
the buccal surface of the crown, increasing the distance from the
root bifurcation to the cervical line
buccallingual
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Roots
Root bifurcation
Starts approx. 4mm below the cervical line
Deep developmental depression present
in line with he lingual groove on the crown4mm
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MESIAL ASPECT
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Mesial surface of mandibular first molar
FEATURES SEEN FROM THIS ASPECT
CROWN OUTLINE
MESIAL MARGINAL RIDGE
SURFACE
ROOT
COMPARISON WITH SECOND PREMOLAR
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Features viewed from the mesial
aspect
?
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MESIAL ASPECT
� 2 cusps and 1 root
mesiobuccal and mesiolingual cusp
mesial root
� Buccolingual measurement of
crown and root > than on the distal aspect
� Crown is rhomboidal in shape
� Entire crown has a lingual tilt in relation to
the root axis
B L
Mesial surface of mandibular first molar
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Crown outline
� Buccal outline
� Lingual outline
� Cervical outline
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� Buccal outline
Convex above the cervical line
± buccal cervical ridge
Above the ridge, it can be less convex
or concave or flat
Mesio buccal cusp is placed over
the buccal third of the mesial root
Crown outline
cervical ridge
B3
M3
L3
BL
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Crown outline
Cervical line
Irregular and curves occlusally towards the center of the mesial surface
Placed at a higher level lingually than buccally when tooth is posed
vertically. When it is lingually tilted as in the oral cavity,
the cervical line is in the same level buccolingually.
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Marginal ridge
� Mesial marginal ridge is confluent with the mesial ridges of
mesiolingual and mesiobuccal cusp
� Placed about 1mm below the level
of the cuspal tips
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Mesial surface of the crown
Convex and smooth over the mesiobuccal and mesiolingual lobes
Concavity at the center of the mesial root
Contact area ± centered buccolingually
on the mesial surface, below
the crest of the marginal ridge
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Mesial root
� Buccal outlineStraight from the cervical line till the middle third
Curves lingually from the middle third to the apex
Apex placed below the mesiobuccal cusp
� Lingual outline
Slanted in a buccal direction
Bluntly tapered apex
Mesial surface is convex with broad concavity
in the middle to the full length of the root
B L
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DISTAL ASPECT
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Distal surface of mandibular first molar
Features seen from this aspect
Distal marginal ridge
Surface of the crown
Cervical line
Developmental groove
Root
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Features viewed from the distal aspect
?
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Features viewed
� Part of all the 5 cusps
� Part of occlusal surface
� Distal marginal ridge
� Distal root
� Part of mesial surface of the crown and root
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Distal marginal ridge
DMR ± short ridge formed by distal cusp ridge of the
distal cusp and distolingual cusp ridge of the
distolingual cusp, meeting at an obtuse angle
A developmental groove or depression crosses
the DMR
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Distal surface of the crown
Distal cusp is seen
DC A ± below the distal cusp ridge
above the cervical linecentered over the distal root
buccal to center point of DMR
Convex surface
Flattened area below the contact area by wear
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Cervical line
Straight or irregular across buccolingually
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Developmental groove
The end of distobuccal developmental groove
is located on the distal surface
Forms a concavity at the cervical portion
of distobuccal line angle
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Root
Flat surface till the apical third
Tapers to a sharp apex
Lingual border of the mesial root is seen
Sometimes a developmental depression is seen
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OCCLUSAL ASPECT
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Occlusal aspect of mandibular first molar
Features viewed
Outline of the crown
Cuspal details
Fossae
Developmental grooves
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Features viewed from occlusal aspect
Greater part of buccal surface
Small portion of lingual surface, lingual to lingual cusp ridges
Mesial and distal marginal ridges
All the 5 cusps with developmental grooves and fossae
Mesial or distal surfaces are not seen
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Crown outline
Hexagonal in form
MD measurement > BL measurement
BL measurement ± mesially > distally
MD measurement ± buccally > lingually
B
L
D M
MD
B
L
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Cuspal details
� Size of the cusps -
1. Mesiobuccal cusp
2. Lingual cusp
3. Distobuccal cusp
4. Distal cusp (also functional)
� Occasionally four cusp molars - quadrilateral
fusion of distobuccal and distal cusp with no distobuccal
developmental groove between them
1
2
3
4
2
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Developmental Fossae
Fossae on mandibular first molar
Major fossa Minor fossa
Central fossa 2Minor Fossae
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Developmental Fossae
Minor fossa
Mesial triangular fossa
� Distal to mesial marginal ridge
� Smaller than central fossa
� Bounded by mesiobuccal cusp, mesiolingual cusp and MMR
MMR
MD
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Developmental grooves
1. Central developmental groove
2. Mesiobuccal developmental groove
3. Distobuccal developmental groove
4. Lingual developmental groove
5. Supplementary grooves
1
23
4
5
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Developmental grooves
MESIOBUCCAL DG
DISTOBUCCAL DG
CENTRAL DG
LINGUAL DG
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Developmental grooves
CENTRAL DEVELOPMENTAL GROOVE
FROM THE CENTRAL PIT ON THE CENRAL FOSS A
MESIAL TRIANGULAR FOSS A JOINING THE MESIOBUCCAL DG IN THE MIDDLE
MESIOBUCCAL DG COURSES IN THE MESIOBUCCAL DIRECTION
SEPERATING THE MESIO AND DISTO BUCCAL CUSP RIDGES
MESIOBUCCAL DG OF THE OCCLUSS AL SURFACE JOINS THE MESIOBUCCAL DG
ON THE BUCACL SURFACE
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Developmental grooves
CENTRAL DEVELOPMENTAL GROOVE
FROM THE CENTRAL PIT ON THE CENRAL FOSS A
DISTAL TRIANGULAR FOSS A JOINING THE DISTOBUCCAL DG IN THE MIDDLE
DISTOBUCCAL DG COURSES IN THE DISTOBUCCAL DIRECTION
SEPERATING THE DISTAL CUSP AND DISTO BUCCAL CUSP RIDGES
DISTOBUCCAL DG OF THE OCCLUSS AL SURFACE JOINS THE DISTOOBUCCAL DG
ON THE BUCACL SURFACE
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Developmental grooves
LINGUAL DEVELOPMENTAL GROOVE
FROM THE CENTRAL PIT ON THE OCCLUS AL SURFACE , TOWARDS THE
LINGUAL DIRECTION, SEPERATING THE 2 LINGUAL CUSP RIDGES
JOINS THE LINGUAL DG ON THE LINGUAL SURAFCE
CENTRAL DEVELOPMENTAL GROOVE
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MD
B
L
CENTRAL DEVELOPMENTAL GROOVE
PULPAL ANATOMYPULPAL ANATOMY
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PULPAL ANATOMYPULPAL ANATOMY
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OCCLUSIONOCCLUSION