Oral Anatomy Concised Review

ORAL ANATOMY
(REVIEW)

1.Tooth numbering systems
2.Dental formula
3.Chronology
4.Individual tooth traits ( similarities and differences)

The dental formula for the primary/deciduous teeth in humans is as follows:

This formula should be read as: incisors, two maxillary and two mandibular; canines, one
maxillary and one mandibular; molars, two maxillary and two mandibular—or 10 altogether
on one side, right or left
A dental formula for the permanent human dentition is as follows:

Tooth Numbering Systems (primary)
The universal system of notation for the primary dentition uses uppercase letters for
each of the primary teeth

Tooth Numbering Systems (Primary)
The symbolic system for the permanent dentition was introduced by Adolph
Zsigmondy of Vienna in 1861 and then modified for the primary dentition in 1874.
Independently, Palmer published the symbolic system in 1870.
The symbolic system is most often referred to as the Palmer notation system in
the United States and less frequently as the Zsigmondy/Palmer notation system.
In this system the arches are divided into quadrants with the entire dentition
being notated as follows:
(┘└ ┐┌)

Example:
lower right central incisor


A two-digit system proposed by Fédération Dentaire Internationale (FDI) for
both the primary and permanent dentitions has been adopted by the World
Health Organization and accepted by other organizations such as the International Association for Dental Research. The FDI system of tooth notation is
as follows. For the primary teeth:

Viktor Haderup of Denmark in 1891 devised a variant of the eight-tooth
quadrant system
Primary teeth were numbered as follows:
upper right, 05+ to 01+; lower left, -01 to -05.

Tooth Numbering Systems (Permanent)
In the universal notation system for the permanent dentition, the maxillary teeth
are numbered from 1 through 16, beginning with the right third molar. Beginning
with the mandibular left third molar, the teeth are numbered 17 through 32. Thus,
the right maxillary first molar is designated as 3, the maxillary left central incisor as
9, and the right mandibular first molar as 30. The following universal notation
designates the entire permanent dentition.


The Zsigmondy/Palmer notation for the permanent dentition is a four-quadrant symbolic
system in which, beginning with the central incisors, the teeth are numbered 1 through 8
(or more) in each arch. For example, the right maxillary first molar is designated as 6, and
the left mandibular central incisor as Í1 .
The Palmer notation for the entire permanent dentition is as follows:

A two-digit system proposed by Fédération Dentaire Internationale (FDI)


Viktor Haderup of Denmark in 1891
devised a variant of the eight-tooth quadrant system in which plus (+) and minus (-)
were used to differentiate between upper and lower quadrants and between right
and left quadrants; in other words, +1 indicates the upper left central incisor and 1indicates the lower right central incisor. Primary teeth were numbered as follows:
upper right, 05+ to 01+; lower left, -01 to -05. This system is still taught in
Denmark.5

Tooth landmarks

cusp

triangular ridge

tubercle

transverse ridge

cingulum

oblique ridge

ridge
marginal ridge

fossa
sulcus

developmental
groove
supplemental
groove
pit
lobe

A cusp is an elevation or mound on the crown portion of a tooth making up a
divisional part of the occlusal surface
A tubercle is a smaller elevation on some portion of the crown produced by an
extra formation of enamel. (These are deviations from the typical form.
A cingulum (Latin word for "girdle") is the lingual lobe of an anterior tooth. It
makes up the bulk of the cervical third of the lingual surface. Its convexity
mesiodistally resembles a girdle encircling the lingual surface at the cervical
third

A ridge is any linear elevation on the surface of a tooth and is named according to its
location (e.g., buccal ridge, incisal ridge, marginal ridge).

Marginal ridges are those rounded borders of the enamel that form the mesial and
distal margins of the occlusal surfaces of premolars and molars and the mesial and
distal margins of the lingual surfaces of the incisors and canines (Figures 1-10, A, and
1-11).

Triangular ridges descend from the tips of the cusps of molars and premolars toward the central
part of the occlusal surfaces.
They are so named because the slopes of each side of the ridge are inclined to resemble two
sides of a triangle.
They are named after the cusps to which they belong, for example, the triangular ridge of the
buccal cusp of the maxillary first premolar.

When a buccal and a lingual triangular ridge join, they form a transverse ridge.
A transverse ridge is the union of two triangular ridges crossing transversely the surface of a
posterior tooth

The oblique ridge is a ridge crossing obliquely the occlusal surfaces of maxillary molars and
formed by the union of the triangular ridge of the distobuccal cusp and the distal cusp ridge of
the mesiolingual cusp

Central fossae are on the occlusal surface of molars. They are formed by the
convergence of ridges terminating at a central point in the bottom of the depression
where there is a junction of grooves.
Triangular fossae are found on molars and premolars on the occlusal surfaces mesial or
distal to marginal ridges .They are sometimes found on the lingual surfaces of maxillary
incisors at the edge of the lingual fossae where the marginal ridges and the cingulum
meet.

A sulcus is a long depression or valley in the surface of a tooth between ridges and cusps, the
inclines of which meet at an angle. A sulcus has a developmental groove at the junction of its
inclines. (The term sulcus should not be confused with the term groove.)
A developmental groove is a shallow groove or line between the primary parts of the
crown or root.

A supplemental groove, less distinct, is also a shallow linear depression on the surface
of a tooth, but it is supplemental to a developmental groove and does not mark the
junction of primary parts.
Buccal and lingual grooves are developmental grooves found on the
Pits are small pinpoint depressions located at the junction of developmental grooves or
at terminals of those grooves. For instance, central pit is a term used to describe a
landmark in the central fossa of molars where developmental grooves join .

A lobe is one of the primary sections of formation in the development of the crown. Cusps
and mamelons are representative of lobes.
A mamelon is any one of the three rounded protuberances found on the incisal ridges of
newly erupted incisor teeth.

Central Incisor

Lateral Incisor

Proximal contacts

Cervico-incisal location

—

Mesial

Incisal third

Junction incisal/middle thirds

Distal

Junction incisal/middle thirds

Middle third

Mesioincisal angle

Sharp right angle

Slightly rounded

Distoincisal angle

Slightly rounded

Distinctly rounded

Mesial profile

Straight

Slightly rounded

Distal profile

Nearly round

Distinctly rounded

Mesiodistal width

Comparatively wide

Comparatively narrow

Pulp horn(s)

3 (facial view)

Usually 2 (facial view)

Lobes

4 (Fig. 4-12, A)

4

Lingual Aspect

Fig. 6-3

Fig. 6-14

Marginal ridges

Moderate

More prominent

Cingulum

Moderately pronounced

More prominent

Fossa

Moderately deep

Deep

Incisal Aspect

Fig. 6-11

Fig. 6-18

Outline

Triangular

Ovoid

Labial

Slightly convex

More convex

Dimensions

Table 6-1

Table 6-2

Crown length (cervico-incisal)

10.5 mm

9 mm

Mesiodistal

8.5 mm

6.5 mm

Cervical

7.0 mm

5.0 mm

Labiolingual

7.0 mm

6.0 mm

Contour height

0.5 mm; Figs. 6-4, 6-5

0.5 mm; Fig. 6-13

Facial/lingual

Both cervical third

Both cervical third

Curvature at CEJ

Table 6-1

Table 6-2

Mesial

3.5 mm

3.0 mm

Facial/Labial Aspect

Crown diameter

Distal
Root
Length

2.5 mm
Figs. 6-3, 6-5, 6-9, 6-10
13.0 mm

Pulp canal(s)

1

Chronology
Eruption
Root completed
Tooth Notations
Universal
International (FDI)
Palmer

Tables 2-3, 6-1
7-8 yr
10 yr
Topic 1
Right: 8; left: 9
Right: 11; left: 21

2.0 mm
Figs. 6-13, 6-19, 6-20
13.0 mm
Less frequent apical accessory
canals
Tables 2-3, 6-2
8-9 yr
11 yr
Topic 1
Right: 7; left: 10
Right: 12; left: 22

Central Incisor

Lateral Incisor

Symmetrical bilaterally

Asymmetrical

Mesial

Incisal third

Incisal third

Distal

Incisal third

Incisal third

Mesioincisal angles

Sharp right angles

Some rounding

Distoincisal angles

Sharp right angles

More rounded than
mesioincisal angle

Curvature at CEJ

Fig. 5-27, Table 7-1

Table 7-2

Mesial

3.0 mm

3.0 mm

Distal

2.0 mm

2.0 mm

Right angle to line
bisecting cingulum

Distolingual twist to line
bisecting cingulum

Symmetry
Proximal contacts

Incisal Aspect
Incisal edge (ridge)

Central Incisor

Lateral Incisor

Pulp horn(s)

1 or 0

Variable; more prominent

Lobes

4

4

Dimensions

Table 7-1

Table 7-2

Crown length (cervicoincisal)

9.0 mm

9.5 mm

Mesiodistal

5 mm

5.5 mm

Cervical

3.5 mm

4.0 mm

Labiolingual

6.0 mm

6.5 mm

Contour height

Less than 0.5 mm; Fig. 7-7 Less than 0.5 mm

Facial/lingual

Both cervical third

Both cervical third

Dimensions

Table 7-1

Table 7-2

Length

12.5 mm

14.0 mm

Pulp (root) canal(s)

Usually 1; 2 possible

1

Crown diameter

Maxillary Incisors

Mandibular Incisors

Central incisor wider than lateral incisor

Lateral incisor wider than central incisor

Wider than mandibular central incisor

Narrowest of incisor class

Marginal ridges and cingulum more
prominent

Marginal ridges and cingulum not prominent

Lingual fossa pronounced, often with a lingual
Lingual fossa shallow without grooves or pits
pit
Crown width greater mesiodistally than
labiolingually

Crown width greater labiolingually than
mesiodistally

Roots rounded in cross section

Roots thin mesiodistally

Incisal edge labial to root axis

Incisal edge lingual to root axis

Maxillary Canine

Mandibular Canine

Mesial

Junction incisal/middle
thirds

Incisal third

Distal

Middle third

Middle third

Mesial Aspect

Wider faciolingually

Narrower, longer

Lingual Aspect

Deeper lingual fossae

Flat lingual surface

Marginal ridges

Pronounced; 2 fossae

Parallel or slightly
converging

Cingulum

Large, centered
mesiodistally

Smaller, may be off
center distally

Lingual pits, grooves

Common

None

Incisal Aspect

Marked asymmetry of
mesial/distal halves

Less symmetry; distal
cusp ridge rotated

Incisal/Proximal Aspects

Cusp tip may be at or
labial to root axis line

Cusp tip lingual to root
axis line

Proximal contacts

Maxillary Canine

Mandibular Canine

Dimensions
Mesiodistal

7.5 mm

7.0 mm

Labiolingual

8.0 mm

7.5 mm

Curvature at CEJ

2.5 mm (mesial)

1.0 mm (distal)

Incisal-cervical

10.0 mm

11.0 mm

Contour height

0.5 mm

Less than 0.5 mm

Facial/lingual

Both cervical third

Both cervical third

Pulp horn(s)

1

1

Lobes

4

4

Terminal (number)

1

Maybe 2

Length

17 mm

16 mm

Root

Chronology
Eruption
Root
completed
Tooth
Notations
Universal
International
(FDI)
Palmer

Maxillary
Canine
11-12 yr

Mandibular
Canine
9-10 yr

13-15 yr

12-14 yr

Right: 6; left:
11
Right: 13; left:
23

Right: 27; left:
22
Right: 43; left:
33

Max First Premolar

Second Premolar

Proximal contacts

Mesial/distal: middle third


Shoulders

Prominent

Narrow

Buccal cusp

Tipped more to distal

Not tipped

Cusp ridges

Longer mesial ridge

Similar

Cusp size, height

Slightly wider, longer

Shorter

Lingual Aspect

Buccal profile visible

Profile not visible

Mesiomarginal groove

Crosses marginal ridge

Does not cross ridge

Mesial concavity

Present

Not present

Facial/Buccal Aspect

Mesial Aspect

Mesial root depression

Present

Present

Profile

Hexagonal

Ovoid

Central groove

Long

Short

Supplemental groves

Usually not present

Many; often present

Lobes

4

4

Pulp horn(s)

2

2

Occlusal Aspect

Dimensions
Cervico-occlusal

8.5 mm

8.5 mm

Mesiodistal

7.0 mm

7.0 mm

Cervical

5.0 mm

5.0 mm

Buccolingual

9.0 mm

9.0 mm

Contour height

Fig. 9-5

Fig. 9-19

Facial/buccal crest

Cervical third

Cervical third

Lingual

Middle third

Middle third

Curvature at CEJ

Figs. 9-4, 9-5

Mesial

1.0 mm

1.0 mm

Distal

0.0 mm

0.0 mm

Length of root

14.0 mm

14.0 mm

Grooves

Distinct, longitudinal

No distinct grooves

Number of roots

Usually 2

1 root

Pulp canal(s)

Often 2

Usually 1

Crown diameter

Chronology

Table 9-1

Table 9-2

Eruption

10-11 yr

10-12 yr

Root completed

12-13 yr

12-14 yr

Tooth Notations

Topic 1

Topic 1

Universal

Right, 5; left, 12

Right, 4; left, 13

International (FDI)

Right, 14; left, 24

Right, 15: left, 25

Palmer

Mand First Premolar

Mand Second Premolar


Figs. 10-2, 10-9

Figs. 10-13, 10-18

Proximal contacts

Fig. 5-7

Fig. 5-7

Cervico-occlusal



Form

Asymmetrical

Bilaterally symmetrical

Lingual Aspect

Fig. 10-3

Fig. 10-14

Buccal profile

All buccal profile seen

None seen

Cusp height

Lingual less than buccal

Buccal/lingual cusps nearly
equal

Mesial Aspect

Fig. 10-1

Fig. 10-15

Occlusal plane

Tilted lingually

Essentially horizontal

Transverse ridge or buccal
triangular ridge

Transverse ridge present
(Fig. 10-1)

No transverse ridge
present (Fig. 10-17)

Occlusal Aspect

Figs. 10-6, 10-11

Fig. 10-17

Outline form

Diamond-shaped

Square

Cusps

2 (Fig. 10-1)

2 or 3 (Fig. 10-20)

Lobes

4

4 or 5

Mand First Premolar

Mand Second PM

Dimensions

Table 10-1

Table 10-2

Crown length (cervicoocclusal)

8.5 mm

8.0 mm

Mesiodistal

7.0 mm

7.0 mm

Cervical

5.0 mm

5.0 mm

Buccolingual

7.5 mm

8.0 mm

Contour height

Figs. 5-27, 10-4

Fig. 10-16

Facial

Cervical third

Middle third

Lingual

Middle third

Middle third

Curvature at CEJ

Table 10-1 (cervical
line)

Table 10-2

Mesial

1.0 mm

1.0 mm

Distal

0.0 mm

0.0 mm

Crown diameter

Root

Table 10-1

Table 10-2

Length

14.0 mm

14.5 mm

Pulp canal(s)

1

1

Pulp horn(s)

1

2

Chronology

Table 2-3; Table 10-1

Table 2-3; Table 10-2

Eruption

10-12 yr

11-12 yr

Root completed

12-13 yr

13-14 yr

Tooth Notations

Topic 1

Topic 1

Universal

Right: 28; left: 21

Right: 29; left: 20

International (FDI)

Right: 44; left: 34

Right: 45; left: 35

Palmer

Maxillary Premolars

Mandibular Premolars

Crowns are trapezoidal*

Crowns are trapezoidal

Mesial Aspect: Fig. 4-16
Crowns are trapezoidal

Crowns are rhomboidal

Buccal and lingual cusps are almost
equal in height

Lingual cusps comparatively much
shorter than maxillary lingual cusps
Lingual cusp tips may be lingual to the
root

Two major cusps of almost equal size
and prominence

Buccal and lingual cusps of uneven
height and prominence

*A trapezoid is a four-sided plane figure having two sides parallel.
A rhomboid is an oblique-angled parallelogram with only the opposite sides equal

Maxillary Molars: Type Traits and Other Characteristics General Characteristics of
All Molars

Height of Contour: Buccal crest is at cervical third; lingual crest is at middle third of
crown

Proximal Contacts: Cervical-occlusal location of mesial contact is at middle third
(toward occlusal third); distal contact is at middle third, slightly toward cervical third
Crown Dimensions: Crowns are wider mesiodistally than cervico-occlusal height

Characteristic

First Molar

Second Molar

Third Molar

Facial/Buccal
Aspect

Figs. 11-4, 11-15

Figs. 11-19, 11-24

Figs. 11-28, 11-33

Dimensions

Widest of three

Middle in width

Smallest of three

Distobuccal cusp
height

Equals
mesiobuccal cusp
height

Slightly less than
mesiobuccal

Much less than
mesiobuccal

Lingual Aspect

Fig. 11-6

Fig. 11-20

Fig. 11-29

Distolingual cusp

Largest distolingual Smaller
cusp
width/height

Usually missing

Lingual root

Widest
mesiodistally

Narrower

Narrowest

Occlusal Aspect

Fig. 11-12

Fig. 11-23

Fig. 11-32

Crown form

Trapezoid to
rhomboid

More rhomboidal

Heart-shaped

Lobes

5

4

3 or 4

Characteristic

First Molar

Second Molar

Third Molar

Dimensions

Table 11-1

Table 11-2

Table 11-3

Crown length
(cervicoocclusal)

7.5 mm

7.0 mm

6.5 mm

Mesiodistal

10.0 mm

9.0 mm

8.5 mm

Cervical

8.0 mm

7.0 mm

6.5 mm

Buccolingual

11.0 mm

11.0 mm

10.0 mm

Contour height

0.5 mm; Fig. 1113

0.5 mm; Fig. 1121

0.5 mm; Fig. 1130

Buccal crest

Cervical third

Cervical third

Cervical third

Lingual crest

Middle third

Middle third

Middle third

Curvature at CEJ

Table 11-1

Table 11-2

Table 11-3

Mesial

1.0 mm

1.0 mm

1.0 mm

Distal

0.0 mm

0.0 mm

0.0 mm

Crown diameter

Characteristic

First Molar

Second Molar

Third Molar

Root

Table 11-1

Table 11-2

Table 11-3

Length, buccal

12.0 mm

11.0 mm

11.0 mm

Length, lingual

13.0 mm

12.0 mm

Chronology

Table 11-1

Table 11-2

Table 11-3

Eruption

6 yr

12-13 yr

17-21 yr

Root completed

9-10 yr

14-16 yr

18-25 yr

Tooth Notations

Topic 1

Topic 1

Topic 1

Universal

Right: 3; left: 14

Right: 2; left: 15

Right: 1; left: 16

International
(FDI)

Right: 16; left:
26

Right: 17; left:
27

Right: 18; left:
28

Palmer

Characteristic

Mand First Molar

Second Molar

Third Molar


Figs. 12-4, 12-14

Figs. 12-18, 12-23

Figs. 12-29, 12-34

Crown size

Largest; widest mesiodistally

Smaller

Smallest

Cusps

5 Cusps: mesiobuccal,
distobuccal, mesiolingual,
distolingual, distal

distobuccal, mesiolingual,
distolingual

distobuccal,
mesiolingual,
distolingual

Groove(s)/pit(s)

1 Mesiobuccal ± pit, 1
distobuccal

1 Buccal ± pit

1 Buccal ± pit

Root(s)

Figs. 12-4, 12-14

Fig. 12-18

Fig. 12-29

Widely separated; nearly
vertical

Close together, parallel;
distally inclined

Most short, fused, less
inclination

Lingual Aspect

Fig. 12-6

Fig. 12-19

Fig. 12-30

Cervix

Crown narrower

Less narrow

Less narrow

Occlusal Aspect

Fig. 12-2

Fig. 12-25

Fig. 12-33

Crown form

Quadrilateral or hexagonal,
pentagonal

Quadrilateral or rectangular

Quadrilateral or ovoid

Lobes

5 (Fig. 4-12, C)

4

4

Pulp horn(s)

5

4

4

Dimensions

Table 12-1

Table 12-2

Table 12-3

Crown length
(cervico-occlusal)

7.5 mm

7.0 mm

7.0 mm

Mesiodistal

11.0 mm

10.5 mm

10.0 mm

Cervical

9.0 mm

8.0 mm

7.5 mm

Buccolingual

10.5 mm

10.0 mm

9.5 mm

Contour height

Figs. 12-7, 12-12

Figs. 12-20, 12-21

Figs. 12-31, 12-32

Buccal crest

Cervical third, 0.5
mm

Cervical third, 0.5
mm

Cervical third, 0.5
mm

Lingual crest

Middle third, 1.0
mm

Middle third, 1.0
mm

Middle third, 1.0
mm

Crown diameter

Curvature at CEJ

Figs. 5-27, 12-12

Fig. 12-12

Fig. 12-32

Mesial

1.0 mm

1.0 mm

1.0 mm

Distal

0.0 mm

0.0 mm

0.0 mm

Root

Fig. 12-7

Fig. 12-21

Fig. 12-31

Length

14.0 mm; Table 1-1

13.0 mm; Table 1-1

11.0 mm; Table 1-1

Eruption

6-7 yr

11-13 yr

17-21 yr

Root complete

9-10 yr

14-15 yr

18-25 yr

Tooth Notations

Topic 1

Topic 1

Topic 1

Universal

Right: 30; left: 19

Right: 31; left: 18

Right: 32; left : 17

International (FDI)

Right: 46; left: 36

Right: 47; left: 37

Right: 48; left: 38

Chronology

Palmer

largest, longest, and strongest root?
Sharpest cusp?
Shortest root?
Largest and tallest cusp?
Cusps from largest to smallest
trigon
fossae size from largest to smallest
2 major fossae
2 minor fossae
largest and deepest fossae?
developmental grooves

Palatal root
-3rd largest on maxilla behind canine and 2nd PM
-most palatal roots have a lingual depression
Distobuccal cusp
distobuccal root
mesiolingual cusp
mesiolingual, mesiobuccal, distobuccal, distolingual, and cusp of Carabelli
-[distobuccal and distolingual may be switched]

triangular arrangement of mesiobuccal, distobuccal, and mesiolingual
cusps
central, distal, mesial triangular, and distal triangular [it is the same on
max 2nd molar]
central and distal
mesial triangular and distal triangular
central
5 of them
-central, buccal, distal oblique, lingual, and transverse groove of the
oblique ridge
-distal oblique and lingual sometimes combined as distolingual groove
Mesiobuccal, distobuccal, & mesiolingual

What cusp tips are visible from the buccal?
What does t he buccal groove parallel?
Does the buccal groove usually have a pit?
root cross section
Is the cusp of carabelli every present unilaterally [just on one side]?

-distolingual is NOT visible
the long axis of the distobuccal root
no
roughly ovoid
-buccodistal will be more rounded than mesial
no

At the center of the crown
exception to the rule
mesial bifurcation
Which is located closer to the cervical line: the mesial bifurcation or the [shorter furcation = longer root, which increases anchorage]
buccal bifurcation?
mesial furcation < buccal furcation < distal furcation
Most apically located bifurcation?
distal bifurcation
How many canals in the mesial root?
2
Occlusally, where is the distal proximal contact located?

Terms
Evidence of calcification
enamel completed
eruption
root completed

Definitions
3 yrs
7yrs
12 yrs
15yrs

Which tooth is the oblique ridge less prominent?

max 2nd molar

which cusp is less developed on the 2nd max molar
than the 1st.

DLi

How many roots on a max 2nd molar?

3; MB,DB, lingual

Which root is the longest?
Which root is the shortest?
Which root is usually straighter?
# roots
# pulp horns
#cusps
# of developmental lobe

Lingual
DBu
DBu
3
4
4
4

What is the occlusal outline shape?

rhomboidal to heart shaped

THE DECIDUOUS DENTITION
-It is also known as the primary, baby, milk or lacteal dentition.
A. Overview.
You will recall that we are diphyodont, that is, with two sets of teeth.
The term deciduous means literally 'to fall off.'

http://www.uic.edu/classes/orla/orla312/DeciduousDent.htm

-There are twenty deciduous teeth that are classified into three classes.
Do you recall the term heterodont?
There are ten maxillary teeth and ten mandibular teeth.
The dentition consists of incisors, canines and molars.

-The dental formula is as follows.

-The notation for deciduous teeth is A though J, K through T. It is 'clockwise'just like it
is for permanent teeth as you look at the patient from in front.

B. Role in development
A person 70 years old will have spent 91% of his/her life chewing on
permanent teeth, but only 6% of his/her chewing career with the
deciduous dentition.
-Although the deciduous teeth are in time replaced by the succedaneous
teeth, the deciduous teeth play a very important role in the proper
alignment, spacing, and occlusion of the permanent teeth.
-The deciduous incisor teeth are functional in the mouth for
approximately five years, while the deciduous molars are functional for
approximately nine years. They therefore have considerable functional
significance. When second deciduous molars are lost prematurely, this
can be very detrimental to the alignment of the permanent teeth.

Development of the Deciduous Dentition
http://what-when-how.com/dental-anatomy-physiology-and-occlusion/development-and-eruption-of-theteeth-dental-anatomy-physiology-and-occlusion-part-1

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II. Formation and Eruption of Deciduous Teeth.
-Calcification begins during the fourth month of fetal life.
By the end of the sixth month, all of the deciduous teeth have begun
calcification.
-Clinical hint: good nutrition is essential.
-By the time the deciduous teeth have fully erupted (two to two and
one half years of age), calcification of the crowns of permanent teeth is
under way. First permanent molars have begun calcification at the time
of birth.
Clinical hint: with deciduous molars, extract with caution.
-Here are some things to know about eruption patterns:
(1) Teeth tend to erupt in pairs.
(2) Clinical hint: look for asymmetry. Take an X-ray film as required.

(2) Usually, lower deciduous teeth erupt first. Congenitally
missing deciduous teeth is infrequent.
Usually, the lower deciduous central incisors are the first to
erupt thus initiating the deciduous dentition.
The appearance of the deciduous second molars completes the
deciduous dentition by 2 to 2 1/2 years of age.

-Note :Eruption dates are variable. Some infants get them
early, others do so late. If the teeth are unduly early or late,
you should inquire about siblings, or the parents themselves.
Timing of eruption 'runs in families.'

Note : Deciduous teeth shed earlier and permanent teeth erupt earlier in
girls.
: The orderly pattern of eruption and their orderly replacement by
permanent teeth is important.

The textbook order for eruption of the deciduous teeth is as
follows:

(1) Central incisor.........Lower 6 ½ months, Upper 7 ½ months
(2) Lateral incisor.........Lower 7 months, Upper 8 months
(3) First deciduous molar...Lower 12-16 months, Upper 12-16
months
(4) Deciduous canine........Lower 16-20 months, Upper 16-20
months
(5) Second deciduous molar..Lower 20-30 months, Upper 2030 months

III. Root Formation and Obliteration
A. In general, the root of a deciduous tooth is completely
formed in just about one year after eruption of that tooth
into the mouth.
B. The intact root of the deciduous tooth is short lived. The
roots remain fully formed only for about three years.
C. The intact root then begins to resorb at the apex or to the
side of the apex, depending on the position of the developing
permanent tooth bud.
D. Anterior permanent teeth tend to form toward the lingual of
the deciduous teeth, although the canines can be the
exception. Premolar teeth form between the roots of the
deciduous molar teeth.

IV. The Transition from the Deciduous to the Permanent Dentition.
A. The transition begins with the eruption of the four first permanent molars, and
replacement of the lower deciduous central incisors by the permanent lower
central incisors.
B. Complete resorption of the deciduous tooth roots permits exfoliation of that
tooth and replacement by the permanent (successional) teeth.
C. The mixed dentition exists from approximately age 6 years to approximately age
12 years. In contrast, the intact deciduous dentition is functional from age 2 - 2 /2
years of age to 6 years of age.
D. The enamel organ of each permanent anterior tooth is connected to the oral
epithelium via a fibrous cord, the gubernaculum. The foramina through which it
passes can be seen in youthful skulls.

V. Differences Between the Deciduous and Permanent Teeth
A. Deciduous teeth are fewer in number and smaller in size but the deciduous molars
are wider mesiodistally than the premolars. The deciduous anteriors are narrower
mesiodistally than their permanent successors.
B. Their enamel is thinner and whiter in appearance. Side by side, this is obvious in
most young patients.
C. The crowns are rounded. The deciduous teeth are constricted at the neck (cervix).
D. The roots of deciduous anterior teeth are longer and narrower than the roots of
their permanent successors.
E. The roots of deciduous molars are longer and more slender than the roots of the
permanent molars. Also, they flare greatly.
F. The cervical ridges of enamel seen on deciduous teeth are more prominent than on
the permanent teeth. This 'bulge' is very pronounced at the mesiobuccal of deciduous
first molars.
G. Deciduous cervical enamel rods incline incisally/occlusally.

MORPHOLOGY OF THE DECIDUOUS TEETH
VI. Deciduous Anterior Teeth.

The primary anteriors are morphologically similar to the permanent anteriors.
-The incisors are relatively simple in their morphology.
-The roots are long and narrow.
-When compared to the permanent incisors, the mesiodistal dimension is relatively
larger when compared to axial crown length. In other words, they look 'squatty,'
especially when worn.
-At the time of eruption, mamelons are not present in deciduous incisors.
-They are narrower mesiodistally than their permanent successors.

VII. Maxillary First Deciduous Molar.
-The notation is B or I.
-It looks a bit like an upper 1st premolar.
-There are three roots.
-It has a strong bulbous enamel bulge that protrudes buccally at the mesial.
-It is the smallest of the deciduous molars in crown height and in the
mesiodistal dimension.

VIII. Maxillary Second Deciduous Molar.
The notation is A or J.
-It looks like a first permanent molar
-There are three roots.
-Usually it has four well developed cusps.
-It is somewhat rhomboidal in outline.
-They often have the Carabelli trait.
-Studies have shown that the shape the maxillary first permanent
molar strongly resembles that of the adjacent deciduous second
molar.

Upper Row: Lower First Molar
Lower Row: Lower First Molar

IX. Mandibular First Deciduous Molar.

-The notation is L or S.
-This tooth doesn't resemble any other tooth. It is unique unto itself.
-There are two roots.
-There is a strong bulbous enamel bulge buccally at the mesial.
-A favorite National Board question asks that you know about the
cusps. The thing to remember is that the mesiolingual cusps on this
tooth is the highest and largest of the cusps.

X. Mandibular Second Deciduous Molar
The notation is K or T.
-This tooth resembles the lower first permanent molar that is
distal to it in the dental arch.
-There are two roots and five cusps. The three buccal cusps are all
about the same size. This is in contrast to the lower first molar
where the 'distal' cusp is smaller that the mesiobuccal and
distobuccal cusps.
-The distal of the three buccal cusps may be shifted of onto the
distal marginal ridge.

Summary
-Upper molars have three roots, lowers have two roots.
-Upper and lower second deciduous molars resemble first
permanent molars in the same quadrant.
-Upper first deciduous molars vaguely resemble upper premolars. Lower first deciduous molars are odd and unique unto themselves.
-First deciduous molars (upper and lower) have a prominent bulge of
enamel on the buccal at the mesial. These help in determining right
and left. (Incidentally, there is a somewhat similar bulge of enamel
seen on the permanent lower second molar. It is helpful in
determining right and left.)

Oral Anatomy Concised Review

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