Dental Anatomy - Lecture 5

8/7/2019 Dental Anatomy - Lecture 5

http://slidepdf.com/reader/full/dental-anatomy-lecture-5 1/18

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Today we will continue talking about morphology of maxillary incisors :

Arch traits:

For Wednesday group we discussed arch traits in the lab; which are the

characteristics that let you distinguish between maxillary incisors as a group &

mandibular incisors as another group... How can we distinguish?First of all, you have to look to the mesiodistal width of

mandibular incisor which is narrower than the mesiodistal

width of maxillary incisor. And we have the proportions,

for example ( pic # 1) if you have this proportion which is the height

( dashed line ) over the width( horizontal line) , height / width = something like

1/2 because the height is greater than the width, but here in

the mandibular tooth ( pic #2 ) it is much greater than the width

so if we divide the height ( 10 mm ) over the width ( 5 mm ),

you will get something like 2, so that's why (height/width)

proportion for mandibular incisor is greater than that of

maxillary incisor. Also we can take mesiodistal (MD)

over labiolingual ( LL ), and this proportion is smaller in mandibular

incisor, why ? let·s see; take the MD (horizontal line pic#2)

(5mm) over the LL (bold line in pic #3) (7mm)

Permanent Mandibular Incisor



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So 5/7 it's 0.8, let's do the same here, the MD (horizontal line pic#1)

(8.5mm) over the LL (bold line pic #4 next page) (7mm), so 8.5/7=1.2 is a "Big

proportion".

The root is conical for maxillary incisor but the root of

mandibular incisor is not. If you do a cross section

in any mandibular incisor you will get an oblong shape

not circular ( oblong means rectangular with soft angles )

.. why do we get this shape ? Because the MD width of the

root is much smaller than the LL .

NOTE : some students in the practical exam get confused between mandibular

CI and maxillary LI; look at the root, if it's oblong then its mandibular incisor

but in the maxillary LI the root is conical.

Type traits:

How can we distinguish between mandibular CI and mandibular LI? They are

nearly equal in size and dimensions, if I give you a maxillary cast and a

mandibular cast; how can I distinguish between them? Look at the two incisors,

if you see the two incisors equal in size then it's a mandibular arch, if you see

the two incisors different in size then it's a maxillary arch, why? because the

maxillary CI is bigger than LI, but actually the difference in size between

mandibular central and mandibular lateral is very small, those are almost equal

in size, that's why if you see two teeth that look alike then this i s a mandibular

jaw, if you see teeth that are different in size then it's a maxillary jaw.



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Labial aspect:

Now let's see this tooth (mandibular CI) from the labial aspect, this tooth is

the narrowest MD of all incisors; in fact it's the narrowest MD of all teeth.

1- The tooth that has the narrowest MD dimension at the?

mandibular CI .

2- The widest tooth MD is the mandibular 1st molar.

3- The longest crown is that of the mandibular canine.

4- The maximum FL (faciolingual) or BL (buccolingual ) width

for any tooth is that for maxillary 1st molar.

Now back to the mandibular CI...

This tooth is the narrowest MD; it's about 5 or 6 mm,

it's bilaterally symmetrical; if you make a line dividing

it into two halves, the right will be similar to the left half.

So it's bilaterally symmetrical ( ).

This tooth has 3 mamelons; mesial, middle and distal.

But actually these mamelons are worn out quickly, that's

why the incisal ridge becomes incisal edge quickly. The

mesial and distal mamelons are of equal prominence

BUT if you remember when we discussed the maxillary

CI, we said that the mesial mamelon has higher shoulder

than the distal one (( refer to dental anatomy lec4 page 11 )).

The mesioincisal angle (1) and distoincisal angle (2) are both 90, but in the

maxillary CI only the MI angle was 90° and the DI one was rounded. The MI



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and DI angles are located at the same level incisocervically (IC) BUT in

maxillary CI the MI angle is higher than the DI one.

Both heights of contour (HOCs) (the filled circles) are at the

same level and they are located close to the incisal edge; within

the incisal third.

Mesial and distal outlines are almost straight lines, CIJ is

convex cervically and the root is narrow and NOT conical.

PS: plz all correct this mistake, in the slide it's (the

root is narrow and conical ) but actually it's not conical.

T he lingual aspect:

It has the features that exist in any incisor; lingual fossa,

two marginal ridges and a cingulum, but the prominence of

these features is very small, meaning that the cingulum and marginal

ridges aren't prominent and the fossa is shallow. This is very

important, these are arch traits because in the maxillary arch

they are very prominent and the fossa is very deep in maxillary

LI.

The CIJ summit is located in the center.

Maybe some of you will ask Qs: this tooth is bilaterally

symmetrical so how can distinguish between mesial and distal

aspects ?

- Actually this is very difficult; you need experience to do that. So

the Dr will avoid asking about this in the exam.



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T he mesial aspect:

The labial HOC (the empty circle) is within the cervical third ,

from HOC toward incisal edge the labial outline is straight .

The root is broad and flat and we see a shallow

depression along the root ( the oval shape ) . Its ovoid in

cross section but if you remember the root cross section in

maxillary CI is round.

Sometimes we have two canals, remember the percentage

of having two canals in this tooth is 30%, in maxillary CI it's

0%.

T he distal aspect:

It's similar to the mesial aspect but the CIJ (cervical line) is less convex or

less curved.

T he incisal aspect:

The tooth looks triangular, the labial surface is flat but in

maxillary CI it's slightly curved. We don't see labial lobe

grooves ; even if we see them in maxillary CI they are faint.

The long axis of the incisal edge (the dashed line) is

perpendicular to the LL line ( the vertical line ) , this is

v ery important because it allows you to distinguish between

mandibular CI and LI ( type trait ) .

The mesial outline and the distal outline are equal in length.



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The pulp is broad BL (LL)( the black line pic #5) but it's very

narrow MD ( the white line pic #6 ) and sometimes we have

two pulp canals in 30% cases. So that's why any dentist do ing

a root canal treatment for this tooth has to remember and

search for another root canal.

This tooth is very similar to the mandibular CI but there are important

features to distinguish between them. We distinguish these teeth

from the incisal aspect; the long axis of the incisal edge ( the bold

line ) is NOT perpendicular to LL line ( the vertical line ).

So in the exam if you want to know if this tooth is mandibular CI or

mandibular LI , look at the incisal edge , if it's perpendicular to the

LL line then it's a mandibular CI, if it's inclined then it's a mandibular LI

and this inclination follows the curvature of the arch, meaning that the incisal

edge goes lingually as it goes distally ; so that's wh y when you see the incisal

edge, the part of it which is closer to the lingual side of the tooth is the distal

part and the part which is away from it is the mesial part.

Mandibular Lateral Incisor



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T he labial aspect:

This tooth is slightly wider than the CI but sometimes the

amount of difference between this tooth and the other is

very small , so it's difficult to distinguish ..

Lack of bilateral symmetry; in this tooth it's not 100%

bilateral symmetric, but to be honest , many teeth that we

use for tooth identification are obtained from old people,

so in these people the incisal edge is worn out, that's why

the mesial half becomes the same as the distal half.

MI angle (the wavy arrow) is sharp generally; sharper than

the DI angle ( the straight arrow) .. The distoincisal angle is

rounded and more cervically situated.

T he lingual and mesial aspects:

- Very identical to the features of the mandibular CI.

T he distal aspect:

- More of the incisal edge is visible , look at this tooth from

the distal aspect, we can see much of the incisal edge , why ?

because the distoincisal angle is slightly lower .. But this feature

isn't true for mandibular CI because the two angles are the same

height.

The pulp is similar to that of central; the possibility of having two canals is

30%.



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The following table has measurements, they aren't required for the exam but

plz remember them for carving.

Now we're going to discuss the incisal relationship ; the relationship between

maxillary CI and mandibular CI, we have many classes «

In normal situation, the incisal edge of the lower incisor should exist exactly in

the lingual fossa of the upper incisor... meaning that the incisal edge of the

lower incisor biting against the fossa of the upper incisor, this is called Class

. but unfortunately this is not true for all of us.

The normal situation is Class .

Because of this relationship we have overlap ping, some people

think that the normal situation is teeth biting edge to edgeand that's true ! When we make a denture for an old man,

this old man wants teeth to bite edge to edge , BUT you have

to remember that incisors are overlapped ( ) « the



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vertical distance between the incisal edge of the lower incisor and

the incisal edge of the upper incisor is called Ov erbite, normally this

should be 2-3 mm. on the other hand , the amount of horizontal distance

between the incisal edge of the upper incisor and the incisal edge of the lowerincisor is called ov erjet. Normally overbite and overjet should be 2-3 mm. if

they exceed 3 or 4 mm then this is abnormal. For example people with 5 mm of

overbite are known to have deep bite and those with less than 2 mm are known

to have shallow bite. People who have edge to edge contact how much of

overbite do they have? 0.

When Some people bite their teeth, their incisors aren't in contact in this

case we have negative overbite, we call it open bite (

).

Similarly for overjet, people with normal overjet should have 2-3 mm of

overjet. People who have maxillary teeth forward; they will have decrease

overjet increase overjet .. People who have edge to edge overlap how much

overjet do they have? 0. People who have the mandibular teeth advanced in

relationship to maxillary teeth, in this case its rev erse (negativ e) ov erjet.

**Now let's discuss Class , Class and Class III incisal relationship«

In orthodontics, any patient going to an orthodontist gets his teeth examined

for incisal relationship.

Class

- As I said, when we have lower incisal edge biting exactly against the lingual

fossa of upper incisor.

Class

- When the incisal edge of the lower incisor bites posteriorly to its normal

situation.

Class III

- When the incisal edge is located anteriorly to its normal situation.



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So edge to edge contact is Class III, more than that we call it reverse overjet.

Also we have further divided class II into two divisions, now in class II, when

you have the incisal edge biting posteriorly to the lingual fossa and the upper

tooth is proclined, this is class II division I ( pic 7 ) , but some people have

the lower incisor biting posteriorly and the maxillary incisor is inclined lingually

( retroclined ) so it's class II division II ( pic 8)



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Always remember that the lower canine emerges before the upper canine,

actually this is the tooth with the maximum difference in emergence,

remember, for example, that the mandibular CI erupts before the maxillaryone, but the amount of difference is maximum 1.5 years (normal situation). But

for canines we have a big difference between the eruption time of mandibular

and maxillary canines. The mandibular canine in Jordanians erupt roughly in the

age of 10 years, but for the maxillary canine it erupts after the age of 12 so

we have two years of difference (it·s the last successor tooth to erupt so that

sometimes when the maxillary canine erupt it goes out " buccally" because

there's no space to it and sometimes it fails to erupt so it's impacted in the

bone). These problems aren't associated with mandibular canines because atthis time they are already erupted.

The mandibular tooth that has a problem with space is the

mandibular 2nd premolar; it's the last tooth to erupt among

successor teeth so it erupts buccally or lingually.

We don't have type traits because we only have one canine.

Class traits:

How can we distinguish canines as a group?

Canines have only a single conical cusp, they don't have an incisal edge, and

they don't have more than one cusp.

It has the longest and thickest root LL; that's why this tooth is very stable...

and when you lose this tooth the shape of your face will be different; you will

look old!!



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This tooth is the only cusp tooth without occlusal surface because it has only

one cusp , in fact it has an incisal surface.

Canines support arch and face musculature; all the muscles of the face are

supported by canines so once you have lost canines, muscles will go inside andyou will look old.

Arch traits:

How can we distinguish the maxillary canine from the mandibular canine?

Simply the upper canine is larger than the lower one.

Also we use this proportion which is very important«

take the upper canine , the height of the crown ( the

dashed line pic #9 ) ( IC ) / the width of crown ( the

horizontal line pic #9 ) ( MD ) , let's assume that it's

11/7 so it's 1.5, take the lower canine ( pic #10) it's

12/6 so it's 2... So IC/MD proportion is smaller in maxillary

canines.

T he labial aspect:

The cusp tip is on a line with the long axis of the tooth so if we

passed a line that divides the tooth into two equal parts , this line

should come in the point of the tip cusp ( like the pic ) .. Because of

The maxillary canine



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that we have the cusp with two sloping ridges ; mesial sloping ridge

and distal sloping ridge. Notice that the mesial sloping ridge

( in circle ) is shorter than the distal one ( in square ) and the

distal is more inclined ( ) .

The mesial HOC (the filled circle) is located at the junction

between the incisal third and the middle third , but the distal

HOC (the empty circle) is located in the middle of the crown.

So if I give you a maxillary canine and ask you to tell me where

is the mesial and where is the distal? .. simply look at the sloping ridges ; the

short sloping ridge is the mesial and the long is the distal ..

also the level of HOC is different.

The mesial outline is slightly convex but the distal outline is markedly convex.

The CIJ is slightly convex cervically ( not incisally as mentioned in the slides so

plz correct it ) .

The labial surface has a labial ridge (the diamond shape above) , because of

this ridge we have two shallow depressions that are called mesiolabial and

distolabial depressions.

y In carving we have to produce these depressions and the labial ridge, thesefeatures aren't present in incisors.

The root is long and narrow.



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T he lingual aspect:

We have two lingual fossae instead of one , why ?

because we have a lingual ridge that divides the lingual

fossa into two lingual fossae , the mesial lingual fossa

(#1) and the distal one (#2).

The Dr. used to ask about these fossae in the exam so remember them.

The crown and root are narrower lingually than labially, so if you make a cross

section in the root it won't be conical, it's triangular.

Well- elevated marginal ridges and labial ridg e, the lingual fossae are deep.

Sometimes we have a lingual pit or developmental groove marking the inner

boundaries of the marginal ridges.

Mesial aspect: the Cusp tip is labial to a line bisecting the tooth LL. This is very

important and it's one of the arch traits , if I draw a line

separating the tooth into equal halves it won't pass through

the cusp tip, it will be situated lingually ; the tip of the cusp is labial

to the bisecting line of the tooth LL. This is important because

in the mandibular canine this isn't the case , in maxillary canine

this line either passes through the cusp tip or labially.

A Thick cervical third, and the HOC (the filled circle) is located

between the cervical and middle thirds.



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Straight from HOC outline toward the cusp tip.

The Lingual outline starts cervically convex then slightly concave then convex

again. HOC is close to cervical line.

Thick incisal ridge, this part (the horizontal line) as you

see here is thick, the Dr. asked us to remember this info

because some students get confused between incisors an d

canines and that's wrong ! So be careful when you carve

the maxillary canine; it's thick .

The root is wider LL than MD with slight longitudinal

concavity and blunt apex .

T he distal aspect:

Similar to the mesial aspect but we have a deeper and

longer longitudinal concavity on the root .

T he incisal aspect:

The tooth isn't symmetrical , remember that

the mesial part ( pic # 11 ) is narrow mesiodistally

( the horizontal line ) but thick labiolingually ( the

dashed line ). The distal part is narrow LL but thick

MD. So take the point of the tip cusp and measure



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the distance to both sides ; the shorter distance is

for the mesial and the longer is for the distal.

It has 3 distinct lobes ; one lobe contain s the tip of the cusp and two lobes

contain the slopes of the cusp.

Prominent convexity of the cingulum, and the pulp has only one canal; this canal

is broad BL (double convex lens), and from the MD it's narrow.

This is the tooth (cross section)

Forgive me for any mistake « I did my best :)

Thanks for the good times Wala2 khdour Haneen kawamleh

Lastly , Leen shawaheen : ´We may be far by distance butFriendship is one mind in two bodies so we never feel that.µ Mashebnt 5alte :p Thanks for being in my life «.

Done By: Eman Tawalbeh

Dental Anatomy - Lecture 5

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