Dental Anatomy 8 (1)

8/2/2019 Dental Anatomy 8 (1)

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Dental Anatomy

Challenge 2010propound

Lecture Notes

Lecture Title: Morphology of PremolarsProfessor Name: Dr. Ashraf AlShawesh

Done By: Dental Anatomy Script Team


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Morphology of Premolars

Today we will talk about the morphology of the premolars which are are

part of the posterior (cheek) teeth .

Q :Why we dont need to say permanent premolars ?

because we dont have deciduous premolar.

Usually premolar erupt from (10-12 years). As you know we have two

premolars, the first erupt earlier than the second , but nearly at the same

period of time. At the age of 12 all premolars must be erupted for the

Jordanian population.

P.S :

(Just for your information)

Jordanian population is very similar to European populations but very

different from African population because usually they erupt teeth much

earlier than us !

Long time ago we used to call premolars bicuspid which means

tooth with two cusps, but nowadays they stop to use this term and use

premolar instead of it, Why?

Because they found that bicuspid is not accurate for one of the

premolar which is the mandibular second premolar , which In

Posterior cheek teeth :

They are the molarsand

premolar in permanent dentition

and in deciduous dentition

posterior teeth are molars only.


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most of the cases this tooth has three cusps instead of two, one

buccal cusp and two lingual cusps.

Class traits:

How we distinguish between the mandibular second premolar

with three cusps and one of the molars like maxillary third molar which

has three cusps?

Its simple as this: look at the numbers of cusps buccally; premolar

should have only one cusp buccallybut molars at least have two cusps

buccally.

So if we have a case where we have a tooth with three cusps we should

identify the buccal area and count the number of cusps , if you found

one cusp buccally so it is premolar, two cusps buccally its molar.

Q: How can we distinguish

premolars as group from

the other teeth?

Usually we must see at

least two cusps, this

means we sometime see

three cusps in the case ofthe mandibular second

premolar.


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Of course the other premolars (1st & 2nd maxillary & 1st mandibular

premolar) its easy to distinguish it because in all of them we have two

cusps only, one cusp buccally and one lingually OR two cusps lingually

in the case of mandibular second premoral .

What do we mean by cusp?

Cusp its an elevation on the occlusal surface of the tooth (posterior

teeth ) or on the incisal surface in the case of the canine , each cusp is

similar to a pyramid has four marginal ridges , each of these margins

called cusp ridge, and we named these cusps according to the direction

they are going to:

cusp ridge goes mesiallymesial cusp ridge

cusp ridge goes distally distal cusp ridge

cusp ridge goes buccally buccal cusp ridge

cusp ridge goes lingually lingual cusp ridge.

And if you remember, we said that the cusp ridge that directed toward

the center of the occlusial surface we call it triangular cusp ridge and

we call two triangular cusp bridges which make one continuous line

transversecusp ridge , if they make oblique line from one corner to

another corner we call it oblique cusp ridge.

Pit : a very small point depression at the maximum depth of the

fossa.

We have developmental groove running and separating the major

parts( susps and marginal ridges) of the tooth ; if we found a groove that

doesnt separate the major parts of the tooth we call it supplemental

groove .

Q ) What are the major components on the occlusal surface of any

tooth?

1. Cusp

2. marginal ridges

So any groove separating between cusps or separating between the

cusps on marginal ridges is a developmental groove.


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Triangular fossa whish is a fossa existing inside marginal ridge .

And finally in addition of triangular fossa also we have central fossa ,

But in premolars of course we dont see central fossa because we only

have one buccal cusp and one lingual cusp .

Maxillary premolars

Arch traits :

How can we distinguish maxillary from mandibular. premolars?

1. If you look at the maxillary arch you will find the first and the

second premolars are much more alike while if you look at the

mandibular arch you will find the two premolars different , so if

you take dental arch and you see two premolars are similar then

this is maxillary arch , if you see two premolars completely

different then this is a mandibular arch .

2. Maxillary premolar have two major cusps that approximately

equal in size and prominence , but in mandibular premolars we ca

notice that the buccal cusp is bigger than the lingual.

3. Also maxilay premolar are wide buccolingualy but constricted

mesodistally, but in the case of mandibular the buccolingual

diameter is similar to the mesodistal diameter .

4. Inclanitaion of the crown in constrat to the root , in the case

Maxillary premolar the crwon is located just on the top of the root

not tilted but in the case of mandibular premolar it tends to be

tilted lingually in constrat to the root , in other words, long axis of

the crown and the root are coinciding in the maxillary premolar, so

the long axis of the crown is in line with the long axis of the root,

but in the mandibular premolar the long axis of the crown makes


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an angle with long axis of the root, why? Because the crown is

tilted lingually.

5. In the maxillary premolars the lingual height of contour is in the

middle third, while in mandibular the lingual height of contours is

very closer to the occlusal surface not in the middle, its high.

So all these 5 points are significant in distinguishing between maxillary

premolars as a group and mandibular premolar as another group.

Maxillary First Premolar

Buccal aspect:

The tip of buccal cusp is distal to the mesiodistal (MD) midline (thisfeature is the opposite when you compared it with the canine because in

the canine the mesial sloping ridge is shorter than the distal slopingridge).

Sloping cusp ridges:- Mesial cusp ridges is long and straight.

- Distal cusp ridges is short and convex.

The proximal outline and the HOCs: Mesial is slightly concave and the HOC is just occlusal to the halfway

point.

It is similar to the buccal aspect of the secondpremolar, but its slightly largerand similar to the

buccal aspect of the canine but slightly smaller .

So this means: the canine should be the largest,

then the first premolar and then the second

premolar. So we have a decrease in size when we go

posteriorly from canine to the second

premolar regarding to the buccal aspect of the

tooth.


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Distal is straight and the HOC is more occlusally located than the

mesial HOC.

The mesio-occlusal (MO) and disto-occlusal (DO) angles areoverhanging. Thats mean: MO and DO bulge outside the outline of the

root. We said this is a type trait, because in the case of maxillary

second premolar if you draw a line for the outline of the root this line will

continue through the mesio-occlusal and disto-occlusal, so we wont find

these angles bulging or overhanging.

A small part of the mesial margin of the lingual cusp can occasionallybe seen.

In buccal aspect there are 3 lobes: Middle lobe, mesial lobe anddistal lobe.

MB and DB depressions and labial ridge.All the time remember wehave buccal ridge similar to the labial ridge of the canine.

Cervical line has a slight convexity toward root apex.

Root is conical similar to that of canine but smaller.

lingual aspect :

The lingual cusp tip is mesial to the midline of the crown (its theopposite of the cusp tip buccally which is located distal to the mesio-

distal halfway of the tooth).

The crown is smaller, this means that the toothbuccally is wider than lingually because of that the

entire buccal outline is visible (we can see buccal

outline not the lin ual .


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No protuberances, ridges or depressions so the lingual surface issmooth.

Root :- 2 apices are visible (buccal and lingual).

- There is a space between the two roots in the apical part but down

we see a depression.

The bifurcation of the root doesnt take place at cervical , it happen at

the junction between middle third and the apical third .

(but in molars the bifurcation of the roots actually happens at the

junction between the cervical third and the middle third.)

The mesial aspect :

The triangular ridges incline at 45 degrees, thats why the two cuspridges make 90 degrees.

The mesial marginal ridge is very prominent and it has a groovewhich is slightly lingualto the mid portion ,this is also a type trait because

in the maxillary second premolar we dont see a groove crossing themarginal ridge.

The buccal HOC is within the cervical third and the lingual HOC is inthe middle of the crown .

The lingual outline is convex and the buccal outline is convex at thebeginning and continue as a straight line.

The buccal cusp is higher than the lingual cusp and thisis a type trait , because in the maxillary second

premolar the high of the two cusps are equal and they

are equal in size.(thats how we can distinguish between

the maxillary first and second premolar).


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The distance between the tips of the cusps is greater in the maxillaryfirst premolar compared to the maxillary second premolar.

Cervical line is convex towards the occlusal.

Mesial interradicular groove (interradicular : between the roots ). Itis also called the canine fossa , because this groove is occupied by the

disto-incisal angle of the canine (which is very prominent ) . it makes the

groove at the root area not occlusaly because the maxillary first

premolar erupts before the maxillary canine .

The Occlusal table is centered over the root trunk. And this is an archtrait because in the mandibular premolar the crown is titled lingually

,thats why is occlusal table is not centered in the mandibular premolar .

(Centered means if you draw a line through the root, it will pass through

the middle portion of the crown )

Roots:We see commonly two roots, bifurcate at the junction between middle

and apical thirds.

Q : What is the percentage of seeing two roots in this tooth?

Its90% and in the 10% of the cases we will see one root but still with

two canals (because there is a depression in the root its possible to

have two canals)

Q: What is the percentage of seeing two canals in this tooth? I

Its almost 100% !

VIP:

Remember that we have two root canal for this tooth .


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Distal aspect:

In the mesial interradicular groove it's start between the root and

continue and also continue to involve part of the crown .So the cervical

part of the crown is also involve in this concavity ,But from the Distal

aspect this groove is only confined to the root so we don't see it crossing

the crown.

More of the occlusal surface may be seen because the distal

marginal ridge is low while the mesial marginal ridge as we said is high

and thats why I cannot see part of the occlusal surface . The distal

interradicular groove is shallower than the mesial one.

Occlusal aspect :

We have very sharp MB and DB angle and this also type trait

because in the maxillary 2

nd

premolar they tend to be rounded .

Similar to the mesial aspect

except that wedont see

marginal ridge groove and we

dont see a concavity in the

The 1st premolar is hexagonal in shape andthis isa type trait and the buccal profile is"V " in shape.


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We have slightly convergent mesial and distal profile they are not

parallel they are converging because the buccal part of the tooth is

wider than the lingual part of the tooth, and this is a type trait because

in the maxillary 2nd premolar the mesial and distal outline seen from

the occlusal view tend to be parallel.

The lingual profile is strongly convex .And also we can see the buccal

ridge and two depressions.

The occlusal table formed by cusps and marginal ridges, we have the

buccal cusp ,lingual cusp , mesial marginal ridge and distal marginal

ridge. The apex of the lingual cusp is located slightly mesial to the

bisecting line buccolingully.

Triangular ridges, of course we see triangular ridge for the buccal

cusp and another one for the lingual cusp they are making a

continues ridge called the "Transverse ridge" . So the transverse

ridge made by the two triangular ridges, these two ridges are

separated by the central groove. The central groove terminate

mesially and distally in the mesial triangular fossa and the distal

triangular fossa and these are bounded by the fossa here ,for

example the mesial fossa is bounded by the mesial marginal ridge

and the transvers ridge .

The mesial marginal ridge is shorter than the distal marginal rdidge.

Pulp :- cross section : its look like kidney shape , because buccally

wider than lingually- longtidual section : the pulp constitricted mesodistally, but in

buccolingually section it is wide.

- In most of the cases we have two roots and two canals and lets

say in less than 10% of the cases we see one root but still we

see two canals , sometimes we see one canal that bifurcate

into two .


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][Sum it up][

On the occlusal surface of the premolar, we can find some

grooves, some ridges and some fossae:

arch traits

Occlusal table is centered over root trunk.

1st & 2nd are much more a like while they are different in mandibular.

Have 2 major cusps approximately equal in size & prominence.

Wider BL than MD while in mandibular BL = MD.

Slight lingual inclination of the crown while mandibular have strongly linguallyinclined crowns.

In maxillary, lingual Height Of Contour (HOC) is in the middle 1/3, while it is inthe occlusal 1/3 in mandibular.

type traits

Overhanging MO & DO angles.

In the Lingual aspect : the Entire buccal outline is visible.

in oclussal aspect : Hexagonal in shape - Sharp MB & DB - Slightly convergent M& D profile.

class traits

At least 2 cusps.

Single buccal cusp with one or more lingual cusps.

Molars must have at least 2 buccal cusps.

Fossae

Tringularfossa

Centralfossa

Grooves

Developmentalgrooves

Supplemental

grooves

Ridges

Tringularridge

Transverseridge

You can enjoy these

flashcards..see this link

http://quizlet.com/3014165/ch

-9-maxillary-premolars-flash-

cards/


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PremolarstMaxillary 1

Buccal Lingual Mesial Distal Occlusal Pulp

1) similiar to themax.canine( slightly smaller )and similar to 2ndpremolar( slightly larger )

2) Tip of the buccalcusp is distal to the

MD midline.

3) Sloping ridges:M is long and

straight, D is shortand convex.

4)Proximal outlinesand HOCs

5) OverhangingMO & DO angles(type traits)

6)A small part ofthe M margin ofthe L cusp canoccasionally beseen

7) 3 lobes (MB, DBand a labial ridge).

8) Cervical line isconvex toward theroot.

9) Root is conical(similar to thecaniens butsmaller).

1) Entirebuccal outlineis visible (typetrait)

2) L cusp tip ismesial to themidline of thecrown

3) Noprotuberances,ridges ordepressions

4) Root

* 2 apices arevisible*Interradiculargroove isvisible

1) Buccal cusp ishigher than lingual

2)Triangular ridgesincline at 45 degrees

3)Mesial Marginalridge

4)Buccal HOC withincervical 1/3 fromwhich a slight lingualinclination towardcusp apex

5)Lingual outline isconvex with HOCwithin middle 1/3

6)Cervical line CL isconvex towardocclusal

7) Mesialinterradicular groove

8) Occlusal table iscentered over roottrunk (arch trait)

9) Roots :* Commonly 2 roots

* bifurcate at thejunction betweenmiddle & apical 1/3s )

1) Similar tomesialexcept:

*more of O.surface canbe seen.No marginalgrooves.

*Noconcavity inC. 1/3.

* Distalinterradiculargroove isshallower

1) Hexagonal.

2) Sharp MBand DB.

3) M and D areslightlyconvergent.

4) L is stronglyconvex.

5) Apex of L.cusp is mesialto the midline.

6)Triangularridges

7) Centralgrooveterminates M& D inTriangularfossae

8)Mesial MR isshorter &interrupterd bymarginalgroove

1) X-section :kidneyshape, wideBL narrowMD.

2) BL.Section :2 pulp horns,

buccal islarger.

3) MD.Section:Similar tocanine.


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Test yourself

1) One of the following is true about the supplemental grooves found in

posterior teeth:

a) They could be the margins of an old restoration.

b) Irregular, indistinct linear depressions that separate the major parts of the tooth.

c) They are the same developmental grooves, just another synonym for it.

d) Irregular, indistinct linear depressions that dont separate the major parts of the

tooth.

2) Only one of the following can be used to distinguish between the maxillary

and that mandibular premolars:

a) 1st and 2nd maxillary premolars are alike, while the mandibular premolars are not.

b) 1st and 2nd maxillary premolars are different, while the mandibular premolars are

alike.

c) Maxillary premolars cusps are different; the buccal cusp is larger than the lingual

cusp while the Mandibular premolars cusps are equal in size.d) Maxillary premolars have a strong inclination of the roots toward the lingual side

while the mandibular premolars have a slight inclination toward the labial side.

3) On the lingual surface of the maxillary 1st premolar:

a) There are 2 depressions and a ridge.

b) A marginal groove can be seen.

c) The Interradicular groove can be seen.

d) 1 lobe or more could be present.

4) The pulp in a Bucculingual section of the Maxillary 1st premolar:

a) is a cigar-shaped.

b) is similar to the exterior of a maxillary canine.

c) is kidney-shaped.

d) 2 pulp horns could be seen.


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5) Each fossa of the triangular fossae that are present on the occlusal surface

of the maxillary 1st premolar contain only a pit and buccal grooves.

a) True.

b) False.

6) Fill in the space:

In the maxillary first premolar the mesial cusp ridge is _____ than the distal cusp

ridge.

1 d

2 a

3 c

4 d5 b

6 longer

Noha Ghazal Rawda Najjar

Hadeel Jaradat Baraah Alslamat

Hebah Ramadnah A9eel Ghawanmeh

Sundos Abu Zaid Ahmed Al Shamary

Salam Bataineh Eman Idkaidek

Eman Nazzal Hibah JarrahAsmaa Almawas Hadeel Sumrian

Abeer M. Dirawi

Dental Anatomy 8 (1)

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