(9) mandibular molars and deciduous incisors

8/6/2019 (9) Mandibular Molars and Deciduous Incisors

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Mandibular permanent 2nd molar:

Buccal aspect:

-Its smaller than 1st M ,but larger than the 3rd M in alldimensions, so as we go posteriorly The size of the tooth gets

smaller (type trait) & it is human trait as well as others like

Gorillas as go posteriorly ,the size gets bigger.

-we have only 2B cusps which are visible from B side

but in the 1st M we have 3 cusps (MB, DB & D) but here

in the 2nd M there are 2 cusps buccally (MB & DB) thats whywe have just 1 B groove between them, not like 1st M as

we have (1 MB & 1 DB) groove as we have 3 cusps here & 2

cusps in the 2nd M

-L cusps are more prominent from buccal aspect & it protrudes (

) above B cusps (type trait) as amount of difference between B

& L cusps is very big in this tooth but difference is very small inmandibular 1st M.

Roots:

-There are 2 roots & much closer to each other & distally inclined,

this is (type trait) as mandibular 1st M roots are farther apart &

not that distally inclined

Lingual aspect:

-Crown is shorter occlusocervical & little of proximal surfaces are

visible.

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-Why we cant see proximal surfaces?

Because this tooth is rectangular in shape

not like mandibular 1st M, as in mandibular

1st M there are 3 cusps 1B& 2L which makes M&D

profile converged L, but in mandibular 2nd

M, there are 2B & 2L cusps with rectangular shaped crown, so we

cant see proximal surface as M & D profile parallel & not

converged lingually.

-M & D profile are less convergent cervically they tend to be more

parallel (of course they converge cervically but not very much) , so

neck of the tooth is less constricted but neck of mandibular 1st M

is wider

Mesial asp ect:

-1 root narrower BL with sharp apex

Distal aspect:

-D cusp is missing (type trait) & this tooth has

4 cusps, so if you want to distinguish between

mandibular 1st M & mandibular 2nd M it is easiest

way, just count the number of cusps

*if u found 5 cusps, it is a mandibular 1st

M

*if u found 4 cusps, it is mandibular 2nd M

- less of B surface is visible (not seen) because the tooth is

rectangular ,so we dont see B surface when we look from D aspect,

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but in mandibular 1st M from D aspect we see part of B surface as

DB line angle is obtuse because of presence of D cusp.

-line angle between B surface & M or D surface is 90 in mandibular

2nd M, so from D aspect u cant see B surface but in mandibular 1st

M the angle between B & D are more obtuse so we can see part of

B surface from D aspect. (Type trait)

-D root is much narrower BL with pointed apex (type trait) as this

trait not evidence in mandibular 1st M.

Occlusal aspect:

-It is rectangular tooth & all angles are nearly Right angles (of

course they are slightly rounded) we have 4 cusps of equal size;

the shape is rectangle not trapezoidal like mandibular 1st PM & 1st

M.

B profile = L profile in length

M profile = D profile in length , so each profile is equal in length

& shape

-most prominent of B profile is in region of the MB cusp-farthest

point , most prominent point B is located M to B groove so it is

located in region of MB cusp ,but in mandibular 1st M the prominent

point is in region of DB cusp

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-maximum BL dimension is just M to B groove this means slightly M

half of the crown is wider BL than D half of the crown & this is not

a feature in mandibular 1st M as in it maximum BL dimension is just

D to MB groove.

-M cusp are wider MD than D cusps slightly this means that B & L

grooves are not 100% located in mid portion of crown MD & this

makes M part of the tooth slightly bigger than D part

*(MB & ML are slightly bigger than D part)

-MRs: straight BL (not curved)

Not crossed by M grooves like in mandibular 1stM

-cross (+) groove pattern: this is the only tooth with this feature,

this is the simplest tooth with cross groove pattern (we have B

groove, L groove, M groove & D groove), M & D grooves called

" central groove "

So if u finds a tooth with cross pattern in the groove system, it ismandibular 2nd M.

-more numerous supplemental grooves (maximum number of

supplementary grooves should be in mandibular 3rd M, so as u go

post. The number of supplementary grooves increases)4


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***Easily in the exam DR. Can bring the drawing for a groove

pattern like last 2 years & ask us to identify it.

Pulp:

-similar to that of 1st M.

-BL section, Usually 2 canals in M root & sometimes 1 canal but

most commonly 2 canals, so in root canal treatment if you are

dealing with mandibular 2nd M most of the time not 100% but 95%

there are 2 canals in M root of mandibular 1st M & great possibility

of 2 canals in 2nd

M ,, sometimes we have 2 canals that meet here atapical 1 / 3 to become 1 root canal.

-so if u are treating mandibular 2nd M & u find 1 canal it is possible,

but possibility of having 2 canal in D root is very very minimum not

like mandibular 1st M as there is 60% of having 2 canals in D root.

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-good possibility to have 2 canals in M root & small possibility to

have 1, but all the time we find 1 canal in D root.

-In cross section (transverse section) u finds that M portion of

pulp champers is greater than D portion.

Mandibular permanent 3rdMolar:

Buccal aspect:

-Very highly variable, roots are short, fused & D inclined.

-always we distinguish this M by looking on the Root,, if they are D

inclined & closed to each other or sometimes fused so it is a

mandibular 3rd M.

Lingual aspect:

-Short crown of highly bulbous outline

() & rounded cusps (not pointed cusps )

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Mesial aspect:

-B&L profile are highly convex & this makes distance betweenapices of M cusps (MB & ML) shorter, so occlusal table is very

small in this tooth & constricted compared with mandibular 1st M.

(As we dont use it in mastication)

Distal aspect:

-almost entire B surface is visible & this angle between B&Dsurface (DB angle) is rounded & obtuse

-D root is narrowest BL &shorter of all mandibular M_ pulp is

similar to mandibular 2nd M.

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mesial distal

Occlusal aspect:-ovoid in shape & as u see all angles are rounded & the crown is

very constricted so occlusal surface is small & constricted.

-M half is wider BL than D half (like mandibular 2nd M).

-B&L profiles converge distally this makes D half of the tooth

small BL than M half.

-highly constricted occlusal table in MD & BL dimensions.

-4 narrow conical cusps.

-highly convex MRs.

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-irregular pit & groove pattern with short grooves (many

supplemental grooves).

-it is the most variable among teeth in morphology but maxillary 3rd

M shares some features with it.

How we can disting uish between maxillary & mandibular 3rd

Molar:

-all the time look at the presence of oblique ridge,, it impossible to

find an oblique ridge in mandibular 3rd M,, but all the time we find

an oblique ridge run obliquely from ML to DB cusps in max 3rd M &

in mandibular 3rd we dont see that the tooth look like this

one>>means we cant see acute & obtuse angels in it.

- In mandibular 3rd M very variable groove pattern, very

constricted occlusal table, cusps are rounded

**Now I want from u to compare this with max 3rd M & here are its

features

(Irregular, many supplemental groove but usually u find here as u

can see acute angles & obtuse ones & u find oblique ridge)

**In the exam most of students mistakes when Dr. Asks them is

this a mandibular or max 3rd M, u can look at the crown

- If it rectangular in shape this is mandibular 3rd M.

- If u see a crown with acute & obtuse angles with an oblique ridge

it is max 3rd M.9


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These tables present the type trait between mandibular 1st, 2nd, & 3rd

molar with difference in diameter.

By this we conclude the anatomy of molars.

Now we will start the anatomy of deciduous teeth & we will continue

this topic in another hall,

Anatomy of deciduous teeth (deciduous dentition):

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First of all, this is a picture for Melbon where dr. took his master

degree. Dr. said: it looks like Irbid, isnt it?? But we dont have balloons

in Jordan.

Set trait:

It is the characteristic which let us to distinguish between deciduous

and permanent teeth; so it is the way that we can quickly tell is this

tooth a deciduous or permanent.

1-size: smaller than permanent as teeth dont grow we need a second set

of dentition, so if the tooth is very small, it is a deciduous one. But if it

is big, it is a permanent one.

2- Crown height / length: ratio is smaller in deciduous as crown is very

short compared with the total length of the tooth.

For example: if total length is 20 mm, in deciduous the crown is 5 or 6

mm but in permanent the crown occupy more of the tooth length.

3- crown width / height: the ratio is greater in deciduous as in

permanent teeth the incisor length of the crown is greater than the11


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width, but in deciduous tooth, the crown is short so the width over the

height will be greater but in permanent the ratio is smaller as the crown

is higher.

4- More bulging B & L cervical ridges:

This is an example of deciduous incisor and this is a permanent incisor,

you will see the B ridge & the L ridge (the cingulum), these are bulging,

this make the neck of the tooth is more constricted.

5- In molars we can distinguish between deciduous and permanent by

the roots:

In deciduous more slender and relatively longer more bowed and flaredoutward, why these need to be bowed and flared? Because we need

room for the crown of the successor premolars.

To distinguish it, sorry for this example; deciduous look like females as

it has a west but permanent it looks like males. Sorry for this but it is

the easiest.

Shorter root trunk (area before bifurcation and trifurcation), if you

have more molar and this molar has root bowed and slender and the

amount of root trunk is very minimum.

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In permanent root trunk occupy 1/3 of the root but in deciduous it

occupies just a very very short distance.

6- We also depend on the color of the tooth as deciduous teeth are

whiter in color as enamel is thinner and pulp champer is large.

Student who make fillings for children they enter the pulp as they

forget that they should dig 1-2 mm without reaching the pulp but in

permanent as it is the normal distance between external surface of

tooth and the beginning of the pulp but in permanent 3-4 mm and in

older people 5 mm (as they have second dentine), but students forget

this fact.

Some class, arch and type traits in permanent dentition are applied to

deciduous dentition; only new traits will be discussed.

All arch traits that dr. will not mention in this lecture are the same

arch traits that are applied to deciduous teeth.

For example we distinguish between maxillary central and maxillary

lateral based on some features like the roundness, this feature is the

same to distinguish between deciduous maxillary central incisor &

deciduous maxillary lateral incisor.

This will not be mentioned just the new features will be mentioned by

the dr.

Deciduous incisors:

Eruption: usually mandibular erupts before maxillary incisors as you

know. And central erupts before lateral ones.

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We dont have mamelons or labial grooves or lobes in deciduous teeth.

The day before the lecture the dr. went to Karak for his searches with

another dr.

This dr. asked Dr. Ashraf about a child tooth: is this tooth deciduous or

permanent?? As it was a big incisor and he cant determine is it

deciduous or permanent.

Dr. Ashraf asked him: does it have mamelons?

Dr. said no. So Dr. Ashraf told him that it is a deciduous tooth because

a newly erupted incisor should have mamelons but incisor withoutmamelons in children which is usually small in size is a deciduous incisor.

Permanent deciduous

Maxillary deciduous central incisor:

The only incisor with MD width is greater than crown height; it is theonly incisor (including deciduous & permanent) with a width greater than

the height of the crown.

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M & D profiles are overhanging (located outside the root outline) but in

permanent teeth D & M profiles are continuous with the root profile.

No labial grooves, no depressions and no lobes, so you dont feel that

this tooth is made of 3 lobes fused together; as there is no mamelons.

The cingulum is very prominent & more incisally located, but in

permanent just the cervical 1/3 is occupied by cingulum but here in

deciduous cingulum occupy the cervical half & usually it has an extension

that extends toward the incisal edge.

Sometime this extension may reach the incisal edge dividing the labial

aspect into 2 portions; ML & DL fossa so in this case we call it lingual

ridge (impossible to find it in permanent central incisor).

Unmarked by pits & grooves (impossible to find them here in deciduous)

Marginal ridges are clearly evidence and very common.

This is a maxillary central incisor, as you can see it is very constricted

from all aspect, cervical part is constricted.

In proximal surfaces, the cervical line is convex incisally

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Conical root with rounded apex and incisal surface is diamond in shape.

Mistakes in practical exams when the dr. bring us a question to identify

a deciduous central incisor usually students think that this tooth is

permanent incisor, how we can distinguish?

All the time look at the constriction, if the cervix is constricted this

tooth is deciduous but if the cervix is not constricted, this tooth is

permanent but of course we look at the size of the tooth.

Always mistakes in mandibular central permanent incisor as it is small in

size so we have to look at the constriction

Maxillary lateral incisor:

Smaller than deciduous central incisor, M & B profiles are more in line

with root profile not overhanging.

DI angle more rounded than MI same feature of maxillary permanent

lateral incisor

Labial aspect is more convex MD but in permanent it was a flat.

L fossa is deeper, mesial marginal ridges are more prominent, cervical

line is similar to that of central incisor and the tooth is rounded from

all of incisal aspect.

Regarding to mandibular central deciduous incisor:

This tooth is bilaterally symmetrical to mandibular permanent centralincisor, MI & DI angles are 90 degree (incisal margin or ridge is

horizontal).

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Prominent cingulum with lingual margin extending incisally but in

mandibular permanent central incisor the cingulum was not prominent

like this. So in deciduous mandibular central incisor the cingulum is moreprominent and the marginal ridges are more prominent too.

Marginal ridges are less marked than in maxillary deciduous, DI &

lingual fossa is shallower.

But all of these features are more prominent in mandibular deciduous

than the permanent so if you want to tell is this tooth a deciduous or

permanent just look at the prominence of these features with the sizeand color. But if less prominence and there is no constriction of cervix

so it is maxillary.

The mandibular central incisor the labial surface is flat MD, not

constricted and not convex & cervical line is similar to that of maxillary

incisor.

The root is 3x the height of the crown.

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Now how we distinguish between mandibular deciduous and permanent

incisor?

1- Compare height of crown to the height of the root (small in

deciduous)

2- Root is narrow conical with pointed apex

Mandibular lateral incisor:

Incisal edge slopes distally, this makes the MI angle, more acute or

more 90 degree than the DI as DI the shoulder is lower & the angle is

more rounded.

D profile is more rounded then M profile; we have greater crown

height/ MD ratio than mandibular central deciduous incisor as this

tooth is not wide MD

LL > MD dimensions.

We have cingulum, fossa, MRs which is similar to those of mandibular

central incisor.

Roots are narrow & conical, apex has D inclination.

D surface has narrow vertical depression.

But how we can distinguish between a mandibular deciduous central &

mandibular deciduous lateral again similar to the way we use to

distinguish between permanent and deciduous.

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central lateral

Look at the tooth from incisal view; if you see incisal edge is

perpendicular to BL line, it is a central.

If you see cervical ridge inclined D&L this is mandibular lateral.

Now lets go to middle hall to complete this lecture there!!!

EnD Of LeCtuRe

Forgive us for any mistake, we wish u best of luck

in your final exams & dont forget we are dentists

of the future

Please ma t5arb60 been el mesial and the molarboth e5tesaron M

We indicate this job to:

Abeer al-hamarneh (my sweet bob corn),

Haneen aqle (elnoom sol6aan, our DJ),

Haneen mohsen (fedeetk, arf3lik el8ob3h ooan7nilk e7tram^_*),

Sara al-7ffar ( lek yaaaaaaaaaa salam),

Ethar Salameh (nutella),

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Sanaa Maali (7beeet),

Rowyda al-m2ani (CNN eldof3a),

Hanan al-kateeb (NASCAFE..97 97)

WDeena (sho mshan, wa5 mneek ya happy girl)

Wbsara7a big thanks lyali wafarlna mo7adaret

2007 thanks dr.

W6b3an ma bnnsa our football team

DONE BY:

HANAN.O.AL-KHATEEB & DEENA.N.RAMADAN

Allah y36eena el3afyh

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(9) mandibular molars and deciduous incisors

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