permanent mandibular molars

8/6/2019 Permanent Mandibular Molars

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PERMANENTPERMANENT

MANDIBULAR MOLARS MANDIBULAR MOLARS

� 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

Shorter height cervico occlusally

MD measurements of all molars > MD measurements of all Mand anteriors

MD > BL measurement

� Perform the major work during mastication

because of

» Bulk due to greater dimensions

» Anchorage due to multiple roots and bifurcated root

Root bifurcation

Mand molar ± MD > BL

Max molar ± BL > MD

MANDIBULARMANDIBULARFIRST MOLAR FIRST MOLAR

( 36 & 46)( 36 & 46)

MANDIBULAR FIRST MOLAR

BASIC MORPHOLOGY

� Largest tooth in the mandibular arch

� Cusps ± 5 cusps

� Buccal cusps ± 2

� Lingual cusps ± 2

� Distal -- 1

� Roots� 2 roots ± mesial root

distal root

Broad buccolingually , widely separated at the apices

CHRONOLOGYCHRONOLOGY

First evidence of calcification 3 - 4 months

Enamel completion 4 - 5 yrs

Eruption 6 - 7 yrs

Root completion 9 yrs

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

NOMENCLATURENOMENCLATURE

SYSTEM TOOTH NUMBER

Zsigmondy and Palmer

Universal 19 , 30

FDI system 46 36

Victor and Haderup

5 ASPECTS

BUCCAL ASPECT

BUCCAL ASPECT OF MANDIBULAR FIRST MOLAR

OUTLINE OF THE CROWN

DEVELOPMENTAL GROOVES

BUCCALSURFACE

Crown outline

TRAPEZOIDAL IN SHAPE WITH LONGER OCCLUS AL SIDE

MD MESIAL OUTLINE

DISTAL OUTLINE

CERVICAL LINE

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

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

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

Developmental grooves

2 grooves buccally

Mesiobuccal DG

Distobuccal DG

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

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

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

� Mesial root

� Distal root

� Root trunk

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

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

Root bifurcation

Located 3mm below the cervical line

Deep developmental depression

progressing cervically

No developmental grooves

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

I beam principle

MD Buccal

Cross section at the furcation level of the root

LINGUAL ASPECT

LINGUAL ASPECT OF MANDIBULAR FIRST MOLAR

CROWN OUTLINES

DEVELOPMENTAL GROOVES

LINGUALSURFACE

Crown outline

� Mesial outline

� Distal outline

� Cervical line

� 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

MMRDMR

Disto lingual cusp

Crown outline

� Cervical line

Irregular

Points sharply towards the

root bifurcation

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

DLDistal

Grooves

Lingual developmental groove

Line of demarcation between two lingual cusps

Travels for a short distance only

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

Mesial and distal roots

Measure 1mm longer than the buccal aspect

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

Root bifurcation

Starts approx. 4mm below the cervical line

Deep developmental depression present

in line with he lingual groove on the crown4mm

MESIAL ASPECT

Mesial surface of mandibular first molar

FEATURES SEEN FROM THIS ASPECT

CROWN OUTLINE

MESIAL MARGINAL RIDGE

SURFACE

COMPARISON WITH SECOND PREMOLAR

Features viewed from the mesial

aspect

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

Mesial surface of mandibular first molar

Crown outline

� Buccal outline

� Lingual outline

� Cervical outline

� 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

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.

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

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

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

DISTAL ASPECT

Distal surface of mandibular first molar

Features seen from this aspect

Distal marginal ridge

Surface of the crown

Cervical line

Developmental groove

Features viewed from the distal aspect

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

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

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

Cervical line

Straight or irregular across buccolingually

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

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

OCCLUSAL ASPECT

Occlusal aspect of mandibular first molar

Features viewed

Outline of the crown

Cuspal details

Fossae

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

Crown outline

Hexagonal in form

MD measurement > BL measurement

BL measurement ± mesially > distally

MD measurement ± buccally > lingually

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

Developmental Fossae

Fossae on mandibular first molar

Major fossa Minor fossa

Central fossa 2Minor Fossae

Developmental Fossae

Minor fossa

Mesial triangular fossa

� Distal to mesial marginal ridge

� Smaller than central fossa

� Bounded by mesiobuccal cusp, mesiolingual cusp and MMR

1. Central developmental groove

2. Mesiobuccal developmental groove

3. Distobuccal developmental groove

4. Lingual developmental groove

5. Supplementary grooves

MESIOBUCCAL DG

DISTOBUCCAL DG

CENTRAL DG

LINGUAL DG

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

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

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

PULPAL ANATOMYPULPAL ANATOMY

OCCLUSIONOCCLUSION

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