Dental Anatomy Script 6

8/2/2019 Dental Anatomy Script 6

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Today we will continue the topic of incisors, last time we finished talking about

maxillary central incisorand now we will talk about maxillary lateral incisor,

Mandibular Central Incisors and Mandibular Lateral Incisors.

Maxillary lateral incisor

-Labial Aspect This tooth is narrower mesodistally and shorter incisocervically than the centralincisor (this is a type trait, because we use these features to distinguish between

maxillary central incisors and maxillary lateral incisors).

Usually the lateral and central incisors have the

same length. But notice that all the angles of this

tooth are more rounded than the angles in the

central incisor, so the mesoincisal angle is rounded

and distoincisal angle is severely rounded.If you remember, those angles in the maxillary

central incisor are less rounded. We said that we

have a sharp mesoincisal angle and slightly

rounded disoincisal angle in the maxillary central

incisor.

The HOC (Height of Contour) is further from the incisal edge, they are located away

from the incisal edge when compared with the central incisor.

The mesial HOC of the maxillary lateral incisor is located at the junction between the

incisal third and the middle third. The distal HOC is located exactly at the middle ofthe crown incisocervically. While in the maxillary central incisor this is located at the

junction between the middle third and the incisal third, which means that the HOC of

the central incisor is higher (more incisally located) than the HOC of the lateral

incisor.

The mesial outline is slightly convex and the distaloutline is severely convex while

in the central incisorthe mesial outline is straight and the distal is slightly convex. The

root is conical and slightly inclined distally.

- Lingual AspectFrom the lingual aspectits similar to the central incisor, with one important

difference which is that all the ridges and the Cingulum is very prominent and

marginal edges are very well formed. And as a result of the very prominent features

lingually the fossa is very deep (again, this is a type trait because we use this to

distinguish between the maxillary central incisor and the maxillary lateral incisor).

If we want to order teeth according to which has the most prominent lingual

features and which one has the least, it will be: [the most prominent] maxillary

lateral incisor, maxillary central incisor, mandibular incisors .


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[Note] A mistake that lots of student make while carving :

Many students when theyre carving they make a very deep lingual fossa and as a

result they get very prominent marginal ridges. Please remember that youre carving

a lateral incisor not a central incisor, there are lots of morphological differences

between the two.

Q: Order the following teeth from those with the deepest fossa to those with the

shallowest fossa or from the most prominent cingulum/marginal ridges to the least

prominent?

A: maxillary lateral incisor, maxillary central incisor, mandibular incisor (the central

and lateral are similar).

Sometimes because we have a very deep fossa we may see a groove running

through (crossing) the cingulum, its called developmental groove. And sometimes

at the deepest portion of the fossa we see somepits. This is important because

sometimes, these pits are areas of plaque accumulation and when they accumulate

plaque they induce caries (class I caries). Thatswhy its not uncommon to see caries

at the lingual surfaces of lateral incisors in particular.

Dens Invaginatus

Sometimes in certain locations the fossa is very deep to the extent that its

communicating with the pulp of the tooth. We call this Dens Invaginatus (a condition

that we will be covering next year in oral pathology). This present problems becauseonce the tooth erupts in the mouth, the outside of the tooth is communicating with

the inside of the tooth, because of that the tooth develops pulpitis and this leads to

very serious problems.

- Mesial Aspect

From the mesial aspect of a maxillary lateral incisor, the cingulum is very convex

because its prominent; the cementoenamel junction (CEJ) of the cervical line is less

curved.

- Distal Aspect similar to the mesial aspect.

-incisal aspect:

1. the tooth is ovoid in outline, because the

tooth is rounded in all regions.

2. It has smaller mesiodistal dimension (MD)

than central.

3. The labial outline is rounded.

4. The mesial Line (ML) and distal line (DL) angles are more rounded.


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The pulp is similar to that of the central incisor, we have the pulp that looks like the

tooth from the outside and we have two pulp horns.

[Note] Many people think that the cusps of the elephant are the canines, but these

are the maxillary lateral incisors.

::rsncisoThe Permanent Mandibular I::

from mandibular incisors as another group)group(How to distinguish the maxillary incisors as aArch traits-

Crown:

1) Narrower mesiodistally (MD).

2) Greater height/width proportion.

3) Smaller mesiodistal (MD)/labiolingual

proportion (LL).

Root:

(LL) proportion.ali1) Smaller mesiodistal (MD)/labiolngu

2) Generally oblong in x-section.

-Type traits (How to distinguish mandibular central incisor from mandibular lateral incisor)

Its not difficult to distinguish between maxillary lateral incisor and maxillary

central incisor, but its difficult to distinguish between the mandibular central incisor

and the mandibular lateral incisor, because these two teeth are nearly equal in size

and dimensions and have prominent different features.

Incisors:entralPermanent Mandibular C

We call the similarities between these two teeth (central and lateral), type traits.

Also because you see these two teeth within the same arch then its also an arch

trait. When you see an arch with two similar incisors then its a mandibular arch, but

when they are different then its a maxillary

arch.

-Labial Aspect:

Its very narrow mesiodistaly; in fact its the

narrowest teeth mesiodistaly of ALL TEETH!


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is exactly the same as themesial halfwhich means thebilaterally symmetricalstI

.halfdistal

mamelons are of equal prominence (in thedistalandMesial.mamelonsIt has 3

maxillary central incisors we said that the mesial mamelon is higher than the distal

one). The mesioincisal and distoincisal angles are both 90 and located at the same

level incesiocervicaly.

The heights of contour (HOC) are also at the same location (level) and very close to

the incisial edge. Both mesial and distal outlines are almost straight lines. The

cementoenamel junction (cervical line) is convex cervically, and the root is narrow

and conical.

-Lingual Aspect:

The fossa here is very shallow. The cingulum and marginaledges are lessprominent because when teeth contact, the edge of the central incisor has to make

contact with the fossa of the upper incisor thats why the fossa of the upper teeth

must be deep but here, what makes contact with the fossa of the lower teeth?

Nothing really so thats why its not that deep. Lastly, the cementoenamel junction

summit is exactly at the center.

- Mesial Aspect:

The labial HOC is within the cervical third, and From HOC toward incisial edge, the

(wide) from mesial or distal aspect andbroadisrootTheis straight.outlinelabial

with roundectanglefrom lingual or labial aspect, so the cross section is rnarrow

angels that we call oblong .

2 Root Canals??

This greater dimension -labiolingualy than

mesiodistaly- makes a 30% possibility of

having 2 root canals in this tooth. So if you

want to do root canal treatment for this

tooth always look for a second root canal.

But In the maxillary central and lateral

incisors the possibility for having 2 root

canals is 0% because the root is conical.

Q: What happens if a dentist removed the pulp tissue from one canal and left the

other canal with pulp tissue without removing it?

A: after a period of time the patient will come back complaining of the pain, because

there is still another canal that you didnt treat.Thats why you have to be aware of


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the 30% possibility of having two root canals in this tooth. Also there is a 30%

possibility of having 2 root canals in the mandibular central incisor.

-Distal Aspect

rootThe.mesial aspectin thethandless curveis(CEJ)ntoenamel junctionthe cemeis broad and flat, sometimes we see a shallowdepression in the center of the root

and its avoiding cross section.

-Incisal Aspect:

the incisal aspect of this tooth is triangular .And the labial surface is flat compared

to the labial surface of the central incisor. Thelabial surface of the maxillary lateral

but here it is flat, the dimension ofylmesodistalor central incisor should be convex

the tooth is greater labiolingualy than mesiodistaly but its not true for the maxillary

incisors and we seldom see labiallobules.

We dont see lobules in the labial surface of this tooth but we see lobules on the

maxillary central incisors. In newly erupted central incisor we see on the labial

surface two shallow grooves marking the junction of the different lobes of the tooth

actuallyesbut we said thesmamelonlobes are theesand we said the margins of the

get worn away easily leaving us the incisal edge (converting the incisal ridge to an

incisal edge).

Long axis of the incisal edge is perpendicular to the labiolingual line. This is very

important because this is the only feature that makes you distinguish betweenmandibular incisors. We said mandibular central incisors look like mandibular lateral

tofeaturebestincisal but cant we distinguish between them?? Actually we can, the

distinguish is the long axis of the incisal edge. This should be perpendicular to the

labiolingual line.

So if we see the labiolingual line -labial to lingual- perpendicular to the incisor edge

ts not perpendicular then its af i. Iincisorcentralmandibularthen the teeth is

mandibular lateral incisor.

How can we know where the distal is and where the mesial is?

-The inclination should always follow the arch of the mandible, so because of that

the part of incisal edge located more lingually is the distal part and the part of the

incisal edge located more labially is the mesial part.

Q: Is it true or false?The incisal edge in the mandibular lateral incisor is

perpendicular to labiolingual line?

A: false.

Pay attention please that the mesial outline equals the distal outline, and that theRemember that we have 30%pulp is wide labiolingualy and narrow mesiodistally.


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.to have 2 root canals in this toothpossibility

Mandibular Lateral Incisors

The mandibular lateral incisor may look similar to the mandibular central incisor,but they are not. They have some unique features that make them different.

-Labial Aspect:

The mandibular lateral incisor is slightly wider mesiodistally than the centralof that tooth doesntlonsmameenerally theG.rybilateral symmetlacksand itincisor

isdistal incisal angelbut thesharpismesial incisal angelThe.shouldersequalhave

see more ofcanweincisal edge,of theinclinationBecause of the.roundedslightly

the incisal edge when we look at the tooth

from the distal aspect. The cementoenamel

.distallyis less pronounced(CEJ)junction

- Lingual & Mesial Aspects:

Almost similar to that of the central.

- Distal Aspect:

more of the incisal edge is visible, CEJ is

less pronounced.

-Incisal Aspect:

feature that make us distinguish between the mandibularThe Most Important

lateral and central incisor is that the incisal edge is not perpendicular to the

labiolingual line (LL). The distoincisal (DI) angel is more towards the lingual surface

and the Mesioincisal (MI) angel is more towards the labial surface. The pulp is

similar to that in the central incisor.

Incisal relationship

Now as we learned about the anatomy of the incisors we should also know the

relationship between them when theyre functioning and in contact with each other

in different ways. We call the different ways of the teeth to contact Classes.

Classes, what are they?

When the incisal edge of the lower incisal is

located exactly at the lingual fossa of the

upper incisor then we call this Class 1. While

when the Lower incisal of the lower incisor is

located posterior to the lingual fossa of the

upper incisor then this is we is known as


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Reverse Overjet (-1)

Reverse overjet occurs when the lower jaw is 'oversized',

or the upper jaw is undersized or a combination of both.

Class 2. When incisal edge of the lower incisor is located anterior to the upper incisor

then this is Class 3.

[Note] Normal people (many of us) have Class 1 case but also a good percent of

people got Class 2 case and in fact, there is a minor percent of those who have theClass 3 case.

Overlap Story

Because Human teeth dont bite edge to edge -except in certain occasions and

problems - we always have overlap (Horizontal overlap and vertical overlap). One of

the overlap called the " Over-Bite " which is when the incisal edge of the maxillary

incisor is located lower than the incisal edge of the mandibular incisors, so the

vertical distance between the two incisal edges is known as Over-Bite .There is

another term known as " Over-Jet " which represent the horizontal distance

between the incisal edge of upper incisal and incisal edge of lower incisal. Normal

situation of Over-Bite and Over-Jet is from two to three millimeters (2-3 mms).

[Note] Monkeys bite teeth over teeth (edge to edge) but humans dont.

Q: The vertical overlap between the mandibular incisors and maxillary incisors is

called??

A: Over-bite.

What Happens in Class II?Because the incisal edge is not in contact , then

the over-bite and over-jet can bei increased

and in this situation we say

that in this case there is " Zero" over-bite

and over-jet .

Types of Class II

* Class II (division I), Class II (division II)

We agreed that in Class II , the incisal edge of thelower incisor is located lingual "more posterior " to


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Mandibular Central Incisor

Mandibular Lateral Incisor

labial lingual Mesial distal Incisal pulp

-The narrowest MD of

all incisors.

-Bilaterally symmetrical

.

-3 mamelons.

-90 MI & DI angles and

are at same level IC

(type traits).

-Both HOCs are within

the incisal third.

-M & D outlines are

almost straight lines.

-CEJ convex cervically.

-Root is narrow &

conical.

-Shallow fossa

& less

prominent

cingulum &

marginal

ridges.

-CEJ summit in

the center.

- Labial HOC within

cervical third

From HOC toward

incisal edge labial

outline is straight

-Root broad & flat

-A shallow

depression in

the midpoint.

-Ovoid in x-section.

-CEJ is

less

curved.

-Triangular.

-Labial surface is flat

compared to max.

incisors.

-Seldom labial lobe

groove .

-Long axis of incisal

edge is

perpendicular to LL

line.

-Mesial outline =

distal outline in

length.

Broa-

d LL

and

narro

w MD

labial Lingual &

mesial

Distal Incisal pulp

-Slightly wider than

central

-Lack of bilateral

symmetry

-MI angle is sharp

while

-DI angle is rounded

& more

-cervically situated

-Nearly

identical to

that of

central

-More of the incisal

edge is visible.

-CEJ is less

pronounced.

-Incisal edge is not

perpendicular to LL line

-DI angle is more toward

lingual

- Similar

to that of

central


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notes about Incisal relations :importantSome

class 1 Incisal edge of the lower incisors lies

exactly at the lingual fossa of upper incisor

class 2 Incisal edge of the lower incisors lies

posterior at the lingual fossa of upper incisor

class 3Incisal edge of the lower incisors lies

anterior at the lingual fossa of upper incisor

Overbite ( vertical overlap )

Overjet ( horizontal overlap )

[Note]: normal distance of overbite and overjet is from 2 to 3 mm

Reverse Overjet( negative ve horizontal overlap ) (Ex: -2 or -3 mm)

Test Yourself:

1) In the mandibular lateral incisor , all of the following is correct EXEPT :

a) labial surface is slightly wider than central

b) labial surface is narower than central

c) ECJ is less pronounced

d) b & e

e) The pulp is larger of central pulp

2) Incisal surface of maxillary lateral incisor is ovoid outline :

a) true b) false

3) Which of the following is correct about mandibular central incisor :

a) in pulp : Broad MD and narrow LL

b) Root is narrow and flat

c) Both HOCs are within the incisal third


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d) CEJ is concave cervically

e) c & d

4) Which of the following situations is considered as class 3 of incisal relations :

a) Incisal edge of the lower incisors lies exactly at the lingual fossa of upper incisor

b) Incisal edge of the lower incisors lies anterior at the lingual fossa of upper incisor

c) Incisal edge of the lower incisors lies posterior at the lingual fossa of upper incisor

5) If the distance of overjet = - 2.5 mm , it is called :

a) Overjet

b) Overbite

c) reverse overjet

d) reverse overbite

Answers

1 d

2 a

3 e

4 b

5 c

Quiz-questions from this lecture:

The tusks of the elephant are its maxillary lateral incisors.

What is the narrowest tooth mesiodistaly? Mandibular central

incisor.Whats the possibility of having two canals in the mandibular

central or lateral incisor? 30%.

The long axis of the incisal edge of a mandibular central incisor

is perpendicular to the labiolingual line.

What does the vertical overlap between the mandibular

incisors and maxillary incisors called? Over-bite.


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Quote of the Day:A dream doesn't become reality through magic; it

takes sweat, determination and hard work.

Abeer M. Dirawi

Hebah Ramadnah Rmz Rabbadi

A9eel Ghawanmeh Russia Al Shboul

Salam Bataineh Ahmed Al Shamary

Sundos Abu Zaid Eman Idkaidek

Eman Nazzal Hibah JarrahSawsan Z. Jwaied Hadeel Sumrien

Rawda Najjar GaYda'a Kana'an

Noha Ghazal

**

: " " .

Dental Anatomy Script 6

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