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Development of The Dentition

Prof. Nadia el Harouni

By the end of this lecture you should be able to:

1- Recognize the normal features of the mouth of the neonate

2- Discuss features of normal occlusion of the primary dentition

3- Understand normal development of the primary to permanent dentition.

4- Recognize the normal pattern of eruption of the permanent dentition.

Humans have two dentitions, the deciduous (primary) and permanent

(secondary)

Dental arches constantly change from birth to adulthood, these changes can

be divided into four stages:

1. Gum pad stage

2. Deciduous dentition stage

3. Mixed dentition stage

4. Permanent dentition stage

A) The Mouth of the Neonate

1. The Gum Pads

The maxillary arch is horseshoe shaped, and the gum pads extend buccally

beyond those in the mandible (wider in every way)

At birth the alveolar processes are covered with gum pads , soon

segmented by transverse grooves into 20 sites of developing teeth

At birth the gum pads are not wide enough to accommodate the

developing incisors which are rotated and crowded in their crypts but

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during the first year of life the jaws grow rapidly in width. This allows

the incisors to erupt in good alignment guided by the pressure of the

tongue and lip.

The lateral sulcus is the groove marking the distal of the canine

segment

The gingival groove is the horizontal groove separating the max.

gum pads from the palate.

The dental groove extends from the incisive papilla to meet the

gingival groove at the canine region then lateral to the molar region

The lower arch is U shaped and the lower gum pad is slightly

everted labially it shows:

The lateral sulcus

The gingival groove: the lingual extension of the gum pads

The dental groove: joins the gingival groove at the canine

region

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2. Neonatal Jaw Relationships.

No precise relationship is seen

Anterior open bite is normal. The tongue fills the space between the gum

pads and rests on the lower lip

3-Precociously erupted primary teeth Natal teeth:A child may be born with teeth already present in the Oral

cavity

Neonatal teeth erupt within the first month of life

Pre-erupted teeth appear within the second and third months of life

85% are deciduous (estimated) (management ?)

tooth age

Mand. centrals 7 months

Max. centrals 9 months

Max. laterals 11 months

Mand. laterals 11 months

Max. & mand. Ds 18 months

Max. & mand. Cs 2 Years

Mand. Es 2 years

Max. Es 2 years

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B) The Primary Teeth and Occlusion.

1. Development of the primary teeth

a) Calcification.

At the fourth month IU

At birth - of the crowns are formed

b) Eruption.

Always a range

c) Teething Only trivial symptoms

d) Size and shape of primary teeth. not much variability as in

permanent

e) Ankylosis of primary teeth:

More common than permanent, Lower more than upper not truly submerged

2- Development of the primary occlusion

a) Primary dental arches.

Ovoid

Generalized spacing

Primate spacing

Slight increase anteriorly from birth till 12 months

Posteriorly more increase

b) Occlusal relations.

No 3 dimensional reln until the eruption of the first molars ,

The normal signs of normal deciduous occlusion include

-Spaced anteriors

-Primate spaces; The deciduous teeth are usually spaced as they erupt.

The spaces mesial to the maxillary canines and distal to the mandibular

canines are slightly wider and known as primate spaces. The spaces that

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exist between the deciduous molars usually close by the time of eruption of

the 1st permanent molars, whereas the spaces between the deciduous

incisors remain till these teeth are replaced by their successors.

-Shallow overbite and overjet

-Almost vertical anteriors

-Ovoid arch form

-CLASS I molar and cuspid relation

-Straight /flush terminal plane which changes into a mesial step by

the age of 6 due to

a) cuspal attrition so the mandible moves forward

b) greater spacing in the mandible than the maxilla

d) Disorders of the primary occlusion.

Variable according to ethnic group and culture

Class III and anterior crossbite

Bruxism: a functional malocclusion.

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The mixed Dentition stage

Transition from deciduous to permanent dentition

It is the period from 6 to about 12 years of age .During this

period both the deciduous and the permanent teeth are

present.

The permanent teeth which follow the deciduous teeth are called

successional teeth ( incisors, canines and premolars) while the

permanent molars are called accessional teeth.

Calcification of the permanent dentition All start after birth except 6s (might)

As the permanent teeth are calcified after birth, they are susceptible to local

and general environmental changes

Eruption:

a) Interrelationships between calcification and eruption.

Eruption is a developmental process that moves the tooth

from its crypt position through the alveolar process into the

oral cavity.

During eruption, the root elongates, the primary root resorbs,

the permanent tooth moves occlusaly and the alveolar

process grows.

Permanent teeth begin their eruptive movement when their

crown is completed.

It takes 2 to 5 years for the posterior teeth to reach the

alveolar crest following completion of their crowns and from

12 to 20 months to reach occlusion after reaching the alveolar

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margin. Roots are completed a few months after occlusion is

attained

It may appear that the incisor erupts first, whereas, in truth, the

molar has preceded it in starting eruption, but is moving so slowly

that the incisor passes by it

b) Factors regulating and affecting eruption.

1- Racial

2- Genetic

3- Mechanical

4- Nutritional (to a lesser extent).

5- Gender differences; Girls usually ahead

c) Timing and variability of eruption

Very variable, no set rules.

N.B. Recently It has been observed that eruption occurs only from 8 pm till

midnight or 1 am (growth hormone release?!) stops during the day or the

tooth intrudes.

d) Sequence of eruption.

Also variable but most common;

maxilla: 6,1, 2, 4, 5, 3, 7, 8

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6,1, 2, 4, 3, 5, 7, 8

mandible: 6, 1, 2, 3, 4, 5, 7,8

6, 1, 2, 4, 3, 5, 7, 8

Unfavorable where 7 erupts before 5

First molars 6 years

6 y

7 y

7 y

8 y

9 y

10 y

11 y

11 y

11 y

12 y

12 y

rs 16-25 y

Mandibular teeth erupt ahead of maxillary teeth except the maxillary

premolars.

e) ectopic eruption: The eruption of a tooth in an abnormal position in the

permanent dentition, usually upper 6 or lower 1,2,3

NB impaction :Failure of a tooth to emerge usually due to insufficient

space ,or supernumerary tooth blocking its path or for no local reasons as

in syndromes.

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f) Factors Determining the tooths position during eruption.

I-intra-alveolar stage:

1-heridity

2-presence of adjacent teeth

3-early loss of deciduous

4-pattern of resorption

5-local pathological conditions

6-general pathology affecting growth.

7-mesial drifting tendency.

II- Pre-occlusion stage

1-lips, cheeks, muscles.

2-objects brought in the mouth.

3-caries and extractions of adjacent Teeth

III- Occlusal stage

All previous in addition to muscles of mastication through forces of

occlusion and the anterior component of force

Uses of the dental arch perimeter

A) Alignment of the permanent incisors

b) space for the cuspids and premolars

c) adjustment of the molar occlusion.

First permanent molar:

1st permanent molars are the keys of the dental arches.

The upper molar is located at the base of the key ridge that descends from

the zygomatic arch.

It is guided into place through

1. the position of the second deciduous molar into a flush terminal plane or

mesial step then they undergo:

2. Early mesial shift through consuming interdental spacing

3. late mesial shift through Leeway space after shedding of E.

4. Differential growth of the mandible.

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Flush terminal plane mesial step distal step

Incisor eruption

a) Mandibular incisors:

The mandibular incisors may erupt before the first molar. They usually erupt lingual to their predecessors.

They may erupt slightly transitionally crowded because of incisor liability

(diff. betn collective mesiodistal dimensions of the permanent incisor tooth

crowns which are larger than their deciduous

predecessors by approximately 5-mm in the

mandible and 7-mm in the maxilla). They

adjust through

1- Interdental spacing

2- Intercanine width increases by growth

3- The primary canines tip distally into the

primate spaces.

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4- The permanent incisors are inclined labially in a wider arch

Lack of space may result in either crowding or premature shedding

of the deciduous canines.

b) Maxillary incisors

Maxillary incisors erupt more labial than their predecessors, thus they erupt

into a larger arch and proclined compared to the upright deciduous incisors,

which in addition to the interdental spaces provide the extra spaces needed

for the larger permanent incisors.

Cuspid and bicuspid eruption.

Leeway space:

The difference in the mesiodistal width between the deciduous

canines and molars and their

successors (permanent canine

and the two premolars) is

known as the ( leeway space)

This mesiodistal difference is

0.9 mm on each side in the

upper arch and 1.7 mm on

each side in the lower arch. This difference in space is occupied

by forward migration of the 1st permanent molar allowing

anteroposterior adjustment of the 1st molars.

a) Mandible;

Most frequent sequence of eruption is 3,4,5

The canine erupts first;

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-It maintains the arch length

-prevents lingual tipping of incisors

The 1st premolar erupts easily but may show some rotation

that corrects itself easily

The 2nd

premolar should erupt before the 2nd

permanent

molar, but if the opposite occurs, the 2nd

molar pushes the 1st

molar mesially blocking out the 2nd

premolar.

b) Maxilla

Sequence of eruption is 4, 5, 3.

First and second premolars usually erupt without difficulty.

Maxillary canine follows a tortuous path of eruption than any other

tooth. At the age of three, it is high in the maxilla with its crown

directed mesially and palataly. It moves towards the occlusal plane

and gradually upright itself. During eruption it presses on the distal

aspect of the lateral incisor root (ugly duckling stage) then it is

deflected to a more vertical position as it approaches the line of

occlusion and closes any remaining spaces between the incisors.

Last tooth to erupt in the maxillary arch is usually the permanent

canines.

There is a late mesial shift of the first molars after shedding of the

second deciduous molars.

Ugly Duckling Stage of Broadbent:

This is fanning out of the crowns of the

upper permanent incisors due to the

pressure of the developing canines that

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lie close to their roots. This is considered a normal variation up to

the age of 8-12 years. Incisor alignment improves as the canines

erupt and canine pressure is transferred from the roots to the

crowns of the incisors. Spaces that might exist between the

maxillary incisors usually disappear.

Second molar eruption.

There is always sufficient space for eruption of the second molar

but f it erupts before the second premolar it might block it out

.why

Third molar eruption:

The appearance of the third molars is the final stage in

establishing the permanent dentition. These teeth usually erupt

between 16 and 25 years of age, but this is characteristically

variable and in many cases they either remain unerupted or fail to

develop completely.

Dimensional changes in the dental arch:

Dental arch width increases correlate highly with vertical

alveolar process growth.

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- Maxillary alveolar processes diverge while the mandibular

alveolar processes are more parallel, so the maxillary width

increase is much greater than the mandibular.

- The intercanine width increases in the maxilla more than the

mandible from 3 to 13 years of age

- The dental arch length and perimeter essentially decrease

with the mesial shift of the first molars and the decrease is

more in the mandible.

References

Moyers RE .Handbook of orthodontics. 4thedition. Medical

publishers, 1988.

Bishara S Textbook of Orthodontics, W.B. Saunders company, 2001

Proffit Contemporary Orthodontics, 4th edition , Mosby 2007.

Handbook of orthodontics. Dibiase , Couborne