Dental Anatomy Script # 10

8/2/2019 Dental Anatomy Script # 10

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Dental Anatomy

Challenge 2010

Propound

Lecture Notes

Lecture Title: Morphology of

molars

Professor Name: Dr. Ashraf AlShawesh

Done By: Dental Anatomy Scripts Team


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Permanent molars are identified and distinguished from the rest of

the teeth because of a number of class traits ,they should have 3 or

more cusps .

# How to distinguish between premolars and molars?

( because some premolars have 3 cusps as mandibular 2nd

premolar )

Very simple, Molars should at least have 2 buccal cusps , where

premolars have only one buccal cusp always , but we can see 2 lingual

cups for premolars .

- Arch Traits (Upper and Lower Molars Differences (

First Roots

maxillary molars have 3 roots , and they are located below the

cups 2 of them buccaly and one lingual

1. MesioBuccal root Below the Mesiobuccal cusp

2. DistoBuccal Root Below Distolbuccal cusp

3. Lingual Root

mandibular molars have 2 roots not necessarily located below the

cusps, They locate below the marginal ridges :

1. Mesial Root 2. Distal Root

Second Crowns

- Maxillary molars : buccolingually width is (11 mm), greater than

mesiodistally width (10 mm)

Mandibular molars : mesiodistal width is (11 mm) greater than

buccolingual width (10 mm) .


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Third Cusps

* Maxillary molars , we see 4 cups :

-Three of them as major and main cusps, Triangular in shape "TRIGON

"

1. mesiobuccal

2. distobuccal

3. Mesiolingual

- And one is lesser extra cups at the corner * Distolingual* Mandibular molars ,we see 4 cups of equal sizes .

FourthOblique Ridge

This is present only in maxillary molars ( Not mandibular ), its is a ridge

that runs obliquely from one corner to another , from the tip of

mesiolingual cusp to the tip of distobuccal cusp.

Fifth Cusps Sizes

The two Buccal cusps in maxillary molars are different in their sizes ,

Plus that the mesiolingual cusp is larger than distolingual cups in

maxillary molars , whereas these two buccal cusps and two lingual are in

equal sizes on mandibular molars.

# Roots

Roots become more distally inclined and also fused as we

go posteriorly.

As you see here (slide 5) in the upper molar the roots are

separated and vertical, as we go posteriorly roots become

closed to each other and also distally inclined, as we go

toward the third molar, the roots become fused and distally inclined.


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This feature is important in distinguishing these teeth without having

these teeth put together [when you hold the teeth separately].

Maxillary permanent first molar

First Buccal aspect

1. The mesiobuccal (MB) and distobuccal (DB) cusps are of equal height,

but they are not of equal size. The bigger is the mesiobuccal but the

distobuccal is smaller.

In this feature we talk about the upper molar, because in the lower

molar the two cusps should be equal in size.

2. The mesiobuccal (MB) is wider.

3. The two cusps mesiobuccal and distobuccal are separated by buccal

groove..B groove, it extents until the halfway then disappears

terminate halfway.

4. The slopes of distobuccal (DB) are steeper, which means the tip of this

cusp is more acute (angled) because slopes are steep not flat, they tend

to be flatter in the case of mesiobuccal cusp.

5. The tip of the mesiolingual cusp can be seen between buccal cusps;

this means there is a huge cusp located lingually which is the

mesiolingual cusp.

The tip of this cusp is not located exactly behind the tip of the

mesiobuccal, it tends to be hider.

6. The mesial profile is highly convex in the occlusal area, but tends to be

flat in the cervical area (2/3s).

7. The mesial height of contour is located at the junction between the

quarter 3 and the quarter 4.

8. The cervical line or the cervical third (1/3) is usually flat or sometimes

concave.

9. The distal profile is entirely convex.


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10. The distal height of contour is located at three fifth (3/5) of the

distance from the cervical line to the tip of the cusp (MR cusp).

* The D HOC is lowerthan the M HOC.

*This is a general feature of all teeth except the mandible first premolar.

11. The cervical line is slightly two curved segments separated by an

apical peak.

(This is not really important, if you want, we can consider it as straight line).

# Buccal surface

1. From the buccal aspect, part of the distal surface is visible. Why?

Because the angle between the buccal surface and the distal surface is

obtuse this why we can see some portion of distal surface.

* Notice that we cannot see any part of the mesial surface. Why?

Because the angle between the buccal surface and the mesial surface is

acute.

2. The cervical third 1/3 is convex, the cervical part of the crown startsflat and then it has subconvixity.

3. The occlusal two thirds 2/3 areflat.

# Roots

1. Three roots are visible: mesiobuccal, distobuccaland lingual(palatal).

2. The bifurcation is the area which root trunks start to divide.*The buccal bifurcation is the area of division for making the

mesiobuccal and distobuccal root is located at the junction between the

cervical third and the

middle third 1/3.

* So if you measure the root from the apex to the cervical line, divided

into three equal thirds, you will find the bifurcation located at the

junction between the middle third and the cervical third.


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3. The shallow vertical groove in the midline of the buccal root trunk.

* The area of the root before division is called the root trunk, usually

this area is about one third 1/3 of the length of the root and tends to be

very small in deciduous teeth.

4. The mesiobuccal and distobuccal roots are narrow and incline toward

each other in the apical third.

* This is a type trait. Why? Because as we go distally toward the second

molar and then to the third molar, the two roots become closure to each

other and distally inclined.

5. The mesiobuccal root apex is in line with the mesiobuccal cusp tip.As we go toward the second molar the roots become closer, thats why

we feel that the distance between the two roots is smaller.

As a general role : if you see a molar and its roots are awayfrom each other and

they are outside the limit of the crown this is an upperfirst molar. But if you see that

the roots are close to each other and the distance between them is smallerthan the

dimension of the crown this is second molar. And if the roots were very close to each

other and sometimesfusedthis is a third molar.

6) The longest of these three roots is the lingual roots, which is visible

between the two other roots.

SecondThe lingual aspect:

1) Two cusps with unequal size.

2)The mesiobuccal is much bigger than the distobuccal, also the

mesiobuccal has a small tubercle on its lingual surface which is called

Tubercle of Carabelli .

3)The mesiolingaul cusp makes 3/5 of the mesiodistal width, and it has a

prominent but blunt apex.


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4)The distolingual cusp is rounded shorter and narrower than the

mesiolingual cusp.

An important type trait:

In the first molar this cusp is larger than the same cusp in the second

molar and also its much larger than that in the third molar -if it is

present - because in many of the cases this cusp is absent in the third

molar.

5) A lingual groove runs between the cusps lingualy, terminates in the

midway on the lingual surface.

6) The mesial profile is convex except in the flat cervical third.

7) The distal profile is entirely convex.

8) The lingual surface:

- Its evenly convex OC. This whole surface is like a part of a sphere

means that the convexity is equal. But in the buccal surface we

have a buccal cervical ridge, and the HOC is not exactly in the

middle thats why its not uniformly convex.

- The lingual groove divides the lingual surface into mesial and

distal segments, and the cusp of Carabelli (if present) is

located all the time on the mesial part or in the mesiolingual cusp

.This actually is racially variant means that it differs from one

population/race to another.

{The Dr. said that he has done a study on the cusp of carabelli, he willput it on e-learning and we have to learn the results.

According to that study Jordanians (Arabs) are very similar to Europeans

because both are Caucasians so the percentage of this trait (cusp of

carabelli) is similar (its a little bit higher in Europeans).

In Asians and black people the percentage is very low.

And in Eskimos its very rare to see this trait.}


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- The term cusp of carabelli shouldnt always be used because its

only classified as a cusp when its very huge , and less than 5% of

the people has a very huge one to call is a cusp , thats why its

called sometimes tubercle of carabelli.And when its not

present, we will have a groove instead, which we call in this case

the negative expression of carabelli trait .

9)Roots:

- The three roots are visible.

- -The Proximal outline of the buccal roots is visible as well.

- -The lingual root: * Is very huge - wide cervicaly and it tends to

go up between the two roots. *Its tapered (means starts wideand gets narrower as we go up) with a blunt apex. *Shallow

vertical depression from the cervical line to 2/3s of the length can

be visible here. *The L root apex is in line with crown midline.

This is a type trait because in the maxillary second molar the apex

tends to go distally.

# The mesial aspect:

1) The maximum mesio-distal dimension (width) is at the cervix

of the crown.

2) The mesio-lingual is higher than the mesio-buccal cusp.

3) The buccal- cervical 1/3 is strongly convex, the HOC buccaly is very

close to the cervical line, but lingually its located halfway.

4) The lingual outline is uniformly convex.

5) The cervical line is slightly convex occlusally .

# Mesial surface :

- the mesialmarginal ridge is marked by several tubercles, its very

often to see the marginal ridges made of by diffusion of number


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of tubercles and this is a one of type traits; because usually we

dont see that in second or third molars this fissure (several

tubercles) only found in the mesial marginal ridges of upper

molars and sometime we find sublimental grooves between this

tubercles.

- the contact area is located between the middle and occlusial

third, and this contact area tends to be wide because this tooth

tend to make contact with the maxillary second premolar at this

area.

- cervical third is flat or concave.

- The occlusial 2/3 are convex.

#Root

- we can see only 2 roots the mesiobuccal and the lingual

- lingual like a banana shape because its curved; its curved

lingually first and then its curved buccally.

- both the mesiobuccal and lingual roots are projected toward

crown profile both of them are projected outside the profile of

the crown .

And its a type traitsbecause we dont see this fissures on second or

third molars also we see the cusp or tubercle of carabilly on the

mesiolingual cusp, at this stage we can call it tubercle and when it

become very huge as big as any of this cusps we call it the cusp of

carabilly

Note : we must be careful about using cusp of carabilly, in your book you can

find cuspof carabilly but in fact its not classified as cusp its only invery low

percentage of people where the size of this elevation is huge to extend that itcan classified as cusp but in many of the situations is small elevation its call

the tubercle of carabilly and it may absent in 50% of population and we dont

have any difference between the male and the female or right and left side of

your mouth so when we call cusp of carabilly thats mean the tubercle of

carabilly depending on the size of that elevation.


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# Distal aspect

1) The distobuccal is more prominence than thedistolingual

2) only a small portion of the mesial cusp are visible because Thedistal marginal ridge is loop thats why we can see part of the

occlusial surface but if we look at the tooth mesialy we will not

see any part of the distal cusp because the mesial marginalridge is high

3) The distal marginal ridge is short and less prominence thanthe mesial marginal ridge

4) The distal marginal ridge does not have tubercle, its nottuberculated

5) The buccal and lingual profiles are similar to those seen on themesial aspect

6) the cervical line is nearly straight its not curved# Distal surface

- it is uniformly convex similar to the lingual surface

# Root

- we see 3 roots from this site, why we only see 2 roots here?-

because mesiobuccal root is wide buccolingualy and its

distobuccal hidden behind it the when we look at the from the

distal aspect we can see three cusps because the distobuccal cusp

is narrower than the mesiobuccal cusp thats why we can see

three cusps.


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# Occlusal surface1) we have 2 angle that are acute, and 2 angle that are obtuse, because

of that this tooth not square in shape its rhomboid( ) in shape, as we

go posteriorly -toward the second molar- the acuteness and obtuseness

increase

2) the acute angles are the mesiobuccal and the distolingual

3) the obtuse angles are the mesolingual and the distobuccal, as weknow each cusp has four ridges from the tip(mesial, distal, lingual and

buccal ), each ridge that participate at the occlusial surface of the tooth

is called triangular ridge, now take this cusp which is the distobuccal

cusp and take the mesiolingual cusp, the mesiolingual cusp its a huge

cusp because of that it participate or connections with the mesiobuccal

and distobuccal at the same time , so the triangular ridge of the

mesiolingual cusp is continuous with the triangular ridge of the

mesiobuccal cusp making one continuous ridge called transverse ridge,

the mesial ridge goes towards the marginal ridge and this cusp not have

distal ridge that goes distally but this ridge goes distobuccaly to make

the oblique ridge, thats why the oblique ridge formed by two parts:

the triangular ridge of the distobuccal cuspthe distal cusp ridge of the

mesiolingual cusp.

Please always remember that the oblique ridge consist of 2 parts :1) The triangular ridge of disto-buccal cusp .

2) Distal-buccal ridge of mesio-buccal cusp .

Normally the distal ridge has to go distaly but in this case it goes disto-buccaly

, so thats why its a distal cusp ridge .thats why we have this marginal ridge .


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# Fosses and Grooves

The area between the mesial marginal ridge and the transverse ridge is

FOSSA mesial triangular fossa . any fossa just located inside a marginal

ridge is called triangular fossa ( its a rule ) .

The fossa located between the transverse ridge and the oblique ridge

this fossa " central fossa ".

We didn't talk about disto-lingual , this is the tip of the cusp . Of course

we dont see permanent lingual ridge for the lingual cusp . WHY ???

because the surface uniformly convex so thats why we see mesial and

distal cusp ridges and this one here is triangular .

The area between the triangular cusp ridge of the disto-lingual cusp

and the mesial ridge DISTAL TRIANGULAR FOSSA .

we have one fossa that is lift , this fossa is located just distal to thetriangular ridge and it's located mesial to the triangular ridge of the

disto-lingual cusp .

Again just distal to the oblique ridge and between the oblique ridge

and the triangular ridge of the disto-lingual cusp , this area , this fossa

is called " distal fossa "

o So thats why this tooth has 4 fossa :

1) 2 triangular fossa .2) one central fossa .

3) one distal fossa .

**What about the grooves ?????

We have the buccal groove , disto-lingualgroove and we have the

central groove .

The central groove starts from the mesial pit to the central pit .


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What about the groove that causes the margin of the oblique ridge ?

its the transverse ridge groove .

# Occlusal table :

The area enclosed between the mesial and distal and also you have to

include the marginal ridges , so the area enclosed inside the mesial and

distal ridge of all cusp and also marginal ridge is called occlusal table .

Occlusal table contains the fossa that we discussed .

# The Pulp

FINALLY THE PULP SYSTEM IN THIS TOOTH , generaly each root has one

canal except the mesio-buccal has 2 canals , this is in 60% of the people .

Q: IN 60% OF PEOPLE HOW MANY CANAL WE HAVE ???

A: 4 canals .

Q: HOW CAN WE HAVE 4 CANALS AND 3 ROOTS ????A: one root contain 2 canal ( mesio-buccal )

Its very very very rare to see more than one root canal in the lingual or

disto-buccal root , but its often to see 2 roots in mesio-buccal canal .

So remember That :

THAT IS POSSIBLE IN 60% OF PEOPLE TO SEE 4 CANALS IN THIS TOOTH ,

EXTRA CANAL SHOULD ONLY EXIST WITHIN OR INSIDE THE MESIO-

BUCCAL ROOY .


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Summary


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Test Yourself

3 or more cusps

At least 2 buccal cusps

One or more lingual cusps

In general 2 or 3 roots

Class Traits

3 roots: 2 B & 1 LCrown: BL > MD dimension

3 major cusps: ML,MB,DB(Lesser-sized DL ,sometimesmissing)

Oblique ridge: ML to DB cusp

B cusps are unequal in size

ML cusp > DL cusp

Arch Traits

DL cusp reduces in size

when going posteriorly &

may be missing in 3rd molar

1st molar is the largest & shows

the least morphological variation

Cusp of Carabelli

Roots become more D inclined &much closer when goingposteriorly

Type Traits


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1) Its possible for the permanent molars to have all the following

except:

a. 2 3 roots.

b. 3 or more cusp, maximum 2 of them are buccal cusps.

c. One or more lingual cusps.

d. 3 or more cusps, minimum 2 of them are buccal cusps.

2) The following is a type trait of the maxillary permanent molar:

a. It has an oblique ridge that runs from the ML to the DB cusp.

b. It has a cusp that is called the cusp of cerabelli.

c. the buccal cusps are unequal in size.

d. Nothings correct.

3) The pulp of the maxillary 1st

molar:

a. has horns that are unequal in size in a MD section.

b. has 3 horns that are equal in size in BL section.

c. Its chamber is narrower in BL section.

d. has 2 horns that are equal in height in a MD section.

4) We can see this on the occlusal surface/table of the maxillary 1st

molar:

a. Obtuse MB, DL angles.

b. A major triangular fossa on the distal side.

c. A minor central fossa.

d. A central fossa that has a central pit and groove.

5) In the Lingual view of the maxillary 1st

molar:a. Only 2 roots are visible.

b. All 3 roots are visible.

c. The lingual root is tapered with a blunt apex.

d. b + c . " " :

"


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, , ".

Noha Ghazal Rawda Najjar

Hadeel Jaradat Baraah Alslamat

Hebah Ramadnah A9eel Ghawanmeh

Sundos Abu Zaid Ahmed Al Shamary

Salam Bataineh Eman Idkaidek

Hadeel sumrain Hibah Jarrah

Asmaa Almawas Abeer M. derawi

Eman nazzal

Dental Anatomy Script # 10

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