‫حيدر‬.‫د‬
‫الزريجاوي‬
12/12/2013
Permanent dentition stage
The permanent dentition stage of dental development starts, after shedding
of the last primary tooth and the eruption of all permanent teeth.
Third molar eruption
The appearance of the third molars is the final stage in
establishing the permanent dentition. These teeth
usually erupt between 17 and 25 years of age, but this is
characteristically variable and in many cases, they
remain unerupted or fail to develop completely, i.e. may
be congenitally absent. As these teeth are the last ones
erupt to the arch, so they are subjected to high amount
of crowding or impaction due to the lack of enough
space for them. Controversy exists as to the effect of third
molar impaction and eruption on mesial drift within the dental arches,
particularly the mandibular, and the subsequent effect that this can have on
the alignment of the incisors. It is likely that third molar eruption, rather
than impaction, does have an effect upon mandibular arch crowding often
seen during the late teenage years, but this effect is one component of a
multifactorial condition and prophylactic third molar extraction is unlikely
to remove the problem.
Characteristics of permanent dentition
Some of the characteristics of the "normal" occlusion in the permanent
dentition stage include the following:
Overlap: In a normally occluding dentition, the
maxillary teeth are labial/buccal to the mandibular
teeth.
Angulations: In the primary dentition stage the teeth
are, in general, vertically positioned in the alveolar bone.
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Orthodontics ……………...……………….…….Development of Occlusion.
On the other hand, in the permanent dentition stage the teeth have
buccolingual inclination and mesiodistal angulations.
Occlusion: With the exception of the mandibular central incisors and the
maxillary third molars, each permanent tooth occludes with two teeth from
the opposite arch.
Arch curvatures: The anteroposterior curvature in the mandibular arch is
called the curve of Spee. The corresponding curve in the maxillary arch is
called the compensating curve. The buccolingual curvature from the one
side to the other is called the Wilson curve.
Overbite and Overjet: The normal Overbite & Overjet often ranges
between 2.0 and 4.0 mm.
Posterior relationships: The maxillary and mandibular molars are in a
Class I occlusion (i.e., the mesiobuccal cusp of the maxillary first molar is in
the buccal groove of the mandibular first molar).
Occlusal changes in the permanent dentition
The dentition does not remain static throughout life. Generally, the dental
arches in males grow larger and for longer than in females during both the
preadolescent and adolescent periods. There is a gradual and progressive
loss in arch length as age increases, particularly in the lower arch of
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Orthodontics ……………...……………….…….Development of Occlusion.
females. The net effect of this is an appearance or increase of lower incisor
crowding.
This crowding occurs before or simultaneously with the eruption of the
wisdom teeth and may take place in treated or untreated persons. It
common belief that this is because of pressure created by the erupting
wisdom teeth. However, the current evidence suggests that these teeth play
a minor role, if any, in this crowding. Individuals with congenitally missing
third molars can also have lower incisor crowding. Therefore, the
extraction of these teeth is not supported to prevent the late incisors
crowding.
Maxillary and mandibular differential growth is considered to have an
effect on the late crowding. Growth of maxilla ceases earlier than
mandible's. Because of overbite, the lower incisors cannot move forward to
the extent of the lower jaw growth but tilt lingually to a smaller
circumference which results in crowding. In addition, the maturation of soft
tissues that occurs during the teenage period may increase the pressure
from lips, causing crowding.
Development of the dental arch
The eruption of primary, followed by permanent dentition usually
associated with changes in the arch dimensions. The first year of life is
characterized by rapid jaw growth in both the anteroposterior and
transverse planes of space. This is particularly marked transversely during
the first six months due to the presence of sutures within the midpalatal
seam of the maxilla and mandibular symphysis. Thereafter, most
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Orthodontics ……………...……………….…….Development of Occlusion.
dimensional change is the result of backward and outward extension of the
alveolar processes.
Arch circumference (perimeter): is the distance measured from mesial
surface of first permanent molar around the arch over contact points and
incisal edges in a smoothened curve to the mesial surface of first permanent
molar of the opposite side.
Arch length (depth): is the distance from the most labial surfaces of the
central incisors to the tangent touching the mesial surfaces of 1st permanent
molars.
Arch width: is the distance measured at the tip of (canine cusp anteriorly
and the buccal cusp of 1st molar posteriorly) of one side to the same point
on the opposite side.
Maxillary arch
Changes in the maxillary arch occur in two different phases during the
occlusion development. During the eruption of the permanent central
incisors, upper dental arch length increases slightly (on average 0.5mm)
because of the more labial eruption of the centrals. Essentially, this eruption
pattern creates a larger dental arch circumference compared with the
position of the primary incisors. An additional increase of approximately
1mm can be seen when the permanent laterals incisors erupt.
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Orthodontics ……………...……………….…….Development of Occlusion.
During 3,4,5, eruption period, arch length
commonly decreases because the leeway
space allows permanent 1st molars to
drift in mesial direction.
During the eruption of the maxillary
permanent incisors, inter-canine width
(measured between primary canines)
increase on average by 3mm. Before or at
time of eruption of permanent canines,
another increase of approximately 2mm
take place in canine to canine distance.
This increase could be due to the distalizing pressure of the erupting
permanent incisors on the canines and the Sutural growth at the midpalatal
suture. A steady increase (total 4-5mm) in the distance between the upper
1st molars can be seen after their emergence.
Mandibular arch
In the lower dental arch, no clinically significant changes occur in the arch
length during the eruption of the lower incisors, as they erupt into the same
arch circumference as the primary incisors. A considerable shorting of the
lower arch length takes place during eruption of 3,4,5. As there is a larger
leeway space in the lower arch than the upper, this allows more anterior
migration of permanent 1st molars, which leads to the shorting of the arch
length by an about 2-3mm during the
transition from primary to permanent
dentition.
In the lower arch width, there is comparable
increase of the inter-canine distance as in the
upper arch occurs during the eruption of the
permanent incisors (3mm on average).
However, unlike in the upper arch, no
additional increase in the inter-canine
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Orthodontics ……………...……………….…….Development of Occlusion.
distance takes place in the lower arch during the later stage of
development. At the emergence of the 1st permanent molars, the distance
increase steadily corresponding to the upper arch.
On balance:
 Following the eruption of mandibular permanent incisors, the arch
width measurements in the lower arch are essentially established.
 After the eruption of the 1st permanent molars, the arch length, in
both arches, does not increase. Actually it may decrease with the
exfoliation of primary molars and the mesial movement of permanent
molars into the leeway space.
 Self-correcting Anomalies are classified based on the stages of
development of occlusion, they are seen in.
1. Gum Pads: Increased Overjet (Retrognathic mandible), Open Bite,
Infantile Swallow
2. Primary Dentition: Anterior Deep Bite, Flush Terminal plane, Primary
Spacing
3. Mixed Dentition: End on 1st Permanent Molar Relation, Ugly Duckling
Stage, <2mm Mandibular lower incisors crowding.
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