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Development of the teeth and
dental occlusion
The Deciduous Dentition
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Deciduous Teeth
• Usual Order of Appearance :
• Central Incisors
2. • Lateral Incisors
'.J~ • First Molars
\J • Canines
f • Second Molars
• Mandibular Teeth Usually Precede
Maxillary in order
of Appearance

The Permanent Dentition

Wf O!ILl>llOOO !XltOOLA~ I ADOl.> :scu.Sequence of eruption of permanent teeth: 1-
first permanent molars
2- central incisors
3- lateral incisors
4-
first premolars
5- second premolars*
6- canines*
7- second permanent molars
8- third permanent molars
Mandibular Teeth Usually Precede Maxillary
in order
of Appearance
I Stages of dental development I
•Gum pads stage
•Primary dentition stage
•Mixed dentition stage
•Permanent dentition stage

i
Primary Dentition Stage
The primary dentition stage extends from the time of
eruption of the primary teeth until the eruption of the
first permanent tooth around 6 years of age. Three
characteristics
of the primary dentition stage are
discussed
in some detail.
1- Overbite
2- Overjet
3- Spacing

A
Overbite: Overbite is the amount of vertical
overlap between the maxillary and mandibular central.
When the incisal edges of the upper and lower
incisors are at the same level, the condition is
described as "edge to edge or zero overbite."
When there is a lack of overlap, the condition is
described as open bite and quantified in
millimeters.
B
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Overjet: Overjet is the horizontal relationship or

the distance between the most protruded maxillary
central incisor and the opposing mandibular central
incisor.
This relationship is expressed in millimeters.
If the maxillary incisors are lingual to the
mandibular incisors, the relationship
is described as an underjet.
The normal range of overjet in the
primary dentition varies between
0 and
4.0 mm.
Over jct Overbite
Spacings: In the primary dentition
stage a child may have generalized
spaces
between · the teeth, localized
spaces,
no spaces, or a crowded
dentition. The presence of spacing in
the primary dentition stage is a
common occurrence.

In addition to the generalized spacings,

localized spacings are often present and
are
referred to as primate spaces.
Such spaces
are present in 87% of the
maxillary arches usually between the lateral
incisors
and canines.
The primate spaces are also present in 78% of
the mandibular arches, usually between the
canines
and first primary molars.
primate spaces

A tooth size-arch length discrepancy

(TSALD) in the form
of crowding is less
common and occurs in approximately
3% of the children in the primary
dentition stage.
Mixed Dentition Stage
The mixed dentition stage starts with the
eruption
of the first permanent tooth, usually
the mandibular ·central incisor, and
is normally
completed
at the time the last primary tooth is
shed.
The mixed dentition period
is characterized by
significant changes in the dentition as a result
of the loss of 20 primary teeth and the eruption
of their succedaneous permanent teeth.

In the early stages of the mixed dentition period

there may be a temporary open bite, usually
either
as a result of the still incomplete eruption
of the incisors or because of mechanical
interference from a persistent finger habit.
During normal development this open bite is
often transitory
in nature; the open bite is
present until the incisors complete their
eruption process, unless the abnormal habit
persists .
Spacing: A diastema is a space between any two
neighboring teeth.
During the mixed dentition
stage the presence of a
midline diastema between the maxillary central
incisors
is a normal occurrence. This is called ugly
duckling stage.
In most cases the size
of the diastema may vary
between 1.0 and 3.0
mm .
These diastemas usually close by the time
the
maxillary canines fully erupt and do not require any
orthodontic intervention.

If the diastema persists in the permanent

dentition stage and
if the patient is concerned,
the dentist may consider closing
it
orthodontically or with composite buildups to
the teeth.
ugly duckling stage

Occlusion: is the way of articulation the

maxillary and mandibular teeth
Class I
The class I occlusion is the normal class. In this case ,
the mesiobuccal cusp
of the maxillary first molar is
aligned with the mesiobuccal groove
of the mandibular
first molar.
Class II
The class 11 relationship is when the mesiobuccal cusp
of the maxillary first molar is found in front compared to
the mesiobuccal groove
of the mandibular first molar.
Class Ill
The relationship is when the class Ill mesiobuccal cusp
of the first upper molar found in the rear with respect to
the mesiobuccal groove
of the oral mandibular first
molar

C
Class I
Class II
Class Ill
The Leeway Spaces:
In general, the sum of the mesiodistal width
of the ·primary canine and the primary first
and second molars is larger than the sum of
their succedaneous teeth(permanent canine
and
first and second premolars)

LEEWAY SPACE

I
l
--- ---
--- -- ----
The leeway space is larger in the mandibular arch than in
the maxillary arch.
On the average, the unerupted canine and premolars are
1.8 mm smaller, per side, in the lower arch. In the upper
arch, the leeway space averages
only 0.9 mm per side.'
The leeway space differential between the
two arches
allows the
first permanent molars to move mesially
relatively more
in the mandibular arch than in the
maxillary arch.
Sometimes the combined sizes
of the unerupted teeth are
larger than the space available. This condition is called a
leeway space deficiency, and dental arch
crowding often
results.

Mandibular Growth In general:

Both the maxilla and mandible grow downward
and forward, but during
this developmental stage
the mandible grows relatively more forward than
the maxilla. It was thought that these relative
growth changes may contribute
to the transition
from an end-to-end
to a Class I molar
relationship .


رفعت المحاضرة من قبل: Mohammed AGHA
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