Transcript OCCLUSION IN THE CHILD ITS DEVELOPMENT AND DYNAMICS

OCCLUSION IN THE
CHILD
ITS DEVELOPMENT AND
DYNAMICS
Eruption of Primary Teeth
• Eruption of the primary dentition begins at 6
months with the appearance of the
mandibular central incisors.
• Incisors erupt between 6-9 months
• First molars erupt 12-14 months
• Canines erupt 16-18 months
• Second molars erupt 20-24 months
• Time of eruption is not particularly important
unless it deviates significantly from these
averages.
Primary Occlusion:
General Characteristics
• Inter-digitation of the primary teeth occurs by age
three.
• The primary dentition does not develop a stable
cusp-fossa occlusion; however, there is less
variability seen in occlusal relationships in the
primary than the permanent dentition. The “crooked
teeth” of the permanent dentition are generally not
seen in the primary dentition.
• The mandibular dental arch occludes within the
maxillary throughout its entire circumference
• Most primary arches are ovoid, with few deviations
from this shape.
Primary Occlusion:
Spacing
• Typically there is generalized spacing among the
anterior teeth.
• No significant increases in spacing occurs after the
primary dentition has completed eruption.
• Characteristically, there are spaces mesial to the
maxillary canine and distal to the mandibular canine.
These spaces are termed primate spaces, as they
are also prominent in the dentitions of other primates.
• Spacing among maxillary anterior teeth ranges
from 0-10 mm with an average of 4 mm. The range
in the mandibular is 0-6 with an average of 3 mm.
Arch Circumference
• Obtained by measuring the length of a curved
line passing over the buccal cusps or incisal
edges of the primary teeth, from the distal
surface of one second primary molar to the
distal surface of its antimere.
• Arch length and arch circumference are
sometimes used interchangeable. This is
incorrect. Factors which alter one will,
however, alter the other.
Arch Circumference
Arch Circumference and arch length
decrease a small amount from the time of
eruption of the second primary molars
until eruption of the first permanent molar.
This decrease is due to the mesial migration
of the second primary molars under the
influence of the eruptive force and path of the
first permanent molars.
Arch Circumference
• As the influence of the eruptive path of the
first permanent molar expresses itself, slight
inter-proximal spacing which may have
existed among the primary molars and canine
will close, rendering these proximal surfaces
more susceptible to caries.
• Inter-proximal caries can shorten the arch
length/circumference, thus reducing space
available for the eruption of the
succedaneous permanent teeth.
Overbite
• The distance which the maxillary incisal
margin closes vertically past the mandibular
incisal margin when the teeth are brought
into centric occlusion.
• The average overbite of the primary dentition
is 2 mm.
• This measurement is sometimes expressed
in terms of the percentage of the clinical
crown covered by the maxillary incisor, e.g.,
20%
Overjet
• The horizontal measurement referring to the
distance between the lingual surface of the
maxillary incisors and the labial surface of the
mandibular incisors when the teeth are in
centric occlusion.
• Average is 1-2 mm in the primary dentition.
• If the primary canines and molars wear
considerable, as occurs with bruxism with
children, there is usually less overbite and
overjet by age 6 than normal.
Molar Relationship
• When the primary dentition is erupted and in
occlusion, the distal surfaces of the upper and lower
second molars form one of three relationships: flush
terminal plane (most common); mesial step, or distal
step.
• The terminal plane relationship of the second
molars is always employed in describing the
primary occlusion. It is significant in that it
determines the position of the first permanent
molars on eruption.
• Full understanding of the importance of this will
become apparent in the discussion of the transition
from the primary to permanent dentitions.
Canine Relationship
• The relationship of the maxillary and mandibular canines is the
most stable one throughout the primary dentition.
• It provides the best indicator of the actual relationship between
the maxilla and mandible.
• Classified as:
– Class One: Mandibular canine inter-digitates in embrasure
between maxillary lateral and canine. Note: Each canine
inter-digitates in the primate space of the opposing
arch.
– Class Two: Any relationship in which the mandibular canine
interdigitates distal to this; typically the cusps will be end to
end.
– Class Three: Any relationship in which the mandibular
canine is mesial to this.
Evaluating the
Primary Occlusion
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Molar Relationship
Canine Relationship
Overbite
Overjet
Inter-dental Spacing
Deviations from normal in tooth
positioning
• Functional disharmonies, e.g., cross
bites
Early Mixed Dentition
Ages 6 -9
Eruption of Molars and
Incisors (Normal Sequence)
1. Mandibular 1st Permanent Molar
2. Maxillary 1st Permanent Molar
3. Mandibular Central Incisor
4. Maxillary Central Incisor
5. Mandibular Lateral Incisor
6. Maxillary Lateral Incisor
6-7 years
6-7 years
6-7 years
7-8 years
8-9 years
8-9 years
* Girls commonly erupt their permanent
teeth earlier than boys.
Relationship of First
Permanent Molars Upon
Eruption
• The relationship of the first permanent molars
on eruption is dependent on the terminal
plane relationship of the second primary
molars, as the eruptive path is along the
distal root of the second primary molar.
Relationship of First
Permanent Molars Upon
Eruption
• Flush Terminal Plane results in End to
End
• Mesial step results in Class I molar
• Distal step results in Class II molar
Molar Relationships
• If the first permanent molar erupts into a
Class I molar relationship this is ideal; this is
a basic component of a normal occlusion.
• It is more common (and normal) for the molar
to erupt into an end to end relationship.
Recall that the most common relationship of
the second primary molars is a flush terminal
plane. We will discuss how this End to End
becomes a Class I molar relationship
subsequently.
Classifying Occlusion In The
Context of Molar Relationship
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Normal Occlusion -- Class I molar
Class I Malocclusion -- Class I molar
Class II Malocclusion -- Class II molar
Class III Malocclusion -- Class III molar
• Inaccurate to say a “Class I
occlusion”
Incisor Transition
The period of the incisor transition, ages
6-9, is a critical one for the developing
dentition. “Will there be adequate space
in the arch space accommodate them?”
The problem for the erupting incisors
can be appreciated by analyzing the
space available in comparison to the
space required.
‘Incisor Liability’
The four maxillary permanent incisors are,
on the average, 7.6 mm larger than the
primary incisors. The four mandibular
permanent incisors are 6.0 mm larger than
the primary incisors. This inverse size
differential is termed the ‘Incisor Liability.’
‘Incisor Liability’ demonstrates, in a significant
way, the challenge Nature has if these larger
permanent incisors are to erupt into an
adequate arch alignment.
Comparison of Mesio-distal
Diameters of Maxillary Incisors
Permanent Centrals (9.0 mm)
18.0 mm
Permanent Laterals (6.4 mm)
12.9 mm
Total Width 30.8 mm
Primary Centrals
Primary Laterals
(6.5 mm)
13.0 mm
(5.1 mm)
10.2 mm
Total Width 23.2 mm
Liability
-7.6 mm
Comparison of Mesio-distal
Diameters of Mandibular
Incisors
Permanent Centrals
Permanent Laterals
(5.4 mm) 10.8 mm
(5.9 mm) 11.8 mm
Total Width 22.6 mm
Primary Centrals
Primary Laterals
(4.2 mm) 8.4 mm
(4.1 mm) 8.2 mm
Total Width 16.6 mm
Liability - 6.0 mm
Overcoming ‘Incisor Liability’
A combination of 4 factors, either singularly or
in combination, overcomes incisor liability:
1.
2.
3.
4.
Inter-dental Spacing of Primary Teeth
Inter-canine Arch Width Growth
Inter-canine Arch Circumference Increase
Favorable Variations in the Size Ratio
Between Primary and Permanent Teeth
Inter-dental Spacing of Primary
Incisor Teeth
• Inter-dental spacing either is present in the
primary arch or it is not, and the amount of
spacing does not change during the primary
dentition.
• Range: 0-10 mm in maxillary; average of 4
0-6 mm in mandibular; average of 3
• Lack of inter-dental spacing in the primary
dentition must be considered a serious
handicap to normal alignment of the
permanent incisors.
Prediction of Crowding In
Mandibular Arch
Inter-dental Spacing
of Primary Incisors
Crowding
No Inter-dental Spacing
Less than 3 mm
3 - 6 mm
More than 6 mm
Crowding of
Permanent Incisors
10 in 10
7 in 10
5 in 10
2 in 10
None
Inter-canine
Arch Width Growth
• There is essentially no increase in inter-canine
arch width during the primary dentition.
• In both the maxillary and mandibular arches, there
are significant increases in arch width growth with
the eruption of both the central and lateral
incisors.
• There is also an increase in arch width in the
maxillary with the eruption of the maxillary
canines; this is not true in the mandibular.
• Boys: 6 mm in maxilla and 4 mm in mandible
Girls: 4.5 mm in maxilla and 3 mm in mandible
Inter-canine Arch Circumference
Increase
• Inter-canine width changes must be further related to
changes in the anterior curvature of the inter-canine
arch segments.
• Permanent incisors erupt slightly labially to the arch
position of the primary incisors, and are more
procumbent.
• This labial positioning of the permanent incisors
increases arch circumference, and therefore
available space for the incisors.
• On average, maxillary central incisors position
themselves 2.2 mm farther anteriorly than primary
incisors; this can increase inter-canine arch
circumference as much as 3.0 mm.
Favorable Variations in the
Size Ratio Between Primary
and Permanent Teeth
If the sizes of the anterior teeth are
smaller than average in comparison to
their primary counterparts, the incisor
liability (which is an average) will be
less.
Operationalizing the Four*
Variables
• Maxillary Arch -- Liability of 7.6 mm
– Inter-dental spacing
4 mm
– Inter-canine growth
4 - 6 mm
– Anterior positioning
2 - 3 mm
• Mandibular Arch -- Liability of 6.0 mm
– Inter-dental spacing
3 mm
– Inter-canine growth
3 - 4 mm
– Anterior positioning
2 - 3 mm
*Reduction of liability due to favorable size
differential not considered.
Clinical Considerations
• The ‘Ugly Duckling Stage’
• Endodontics on Permanent Incisors
and First Permanent Molars
‘Ugly Duckling Stage’
• The period from the eruption of the lateral
incisors to the eruption of the canine has
been referred by Broadbent as the ‘ugly
duckling stage.’ It is an apt term, signifying an
relatively unesthetic metamorphosis leading
to an esthetic result.
• During this period parents become worried. A
space may develop between the maxillary
centrals. The laterals flare.
• Occasionally an unknowing dentist will
sacrifice a labial frenum in an effort to
removed the supposed cause of the problem.
‘Ugly Duckling Stage’
• During this time period the crowns of the
developing canines impinge on the
developing roots of the lateral incisors, driving
the roots medially and causing the crowns to
flare laterally.
• With the further migration of the canine
occlusally, the point of influence of the
canines on the laterals shifts incisally so that
eventually the lateral crowns are driven
medially, effecting closure of the space
between the centrals.
Root Closure of Permanent
Incisors and First Molars
• Root closure of the permanent incisors
and 1st permanent molars is not
effected until after age 9. This is
clinically significant in considering root
canal therapy for these teeth.
• Root formation completed:
– First Molars:
– Mandibular Incisors:
– Maxillary Incisors:
9-10
9-10
10-11
Late Mixed Dentition
Ages 9 -12
• Eruption of Canines and Premolars
• Leeway Space
• Overbite and Overjet
• Clinical Considerations
Eruption of Canines and
Premolars (Normal Sequence)
1. Mandibular Canine
2. Maxillary 1st Premolar
3. Mandibular 1st Premolar
4. Maxillary 2nd Premolar
5. Mandibular 2nd Premolar
6. Maxillary Canine
7. Mandibular 2nd Molar
8. Maxillary 2nd Molar
( 9-10 years)
(10-11 years)
(10-12 years)
(10-12 years)
(11-12 years)
(11-12 years)
(11-13 years)
(12-13 years)
‘Leeway Space’
• Just as a size differential existed
between the primary and permanent
teeth in the anterior segment, there is
also a size differential in the posterior
segments.
• The term ‘leeway space’ was coined by
Nance to describe this differential.
Magnitude of the ‘Leeway
Space’
• The combined width of the mandibular
primary canine, and first and second primary
molars are, on the average, 1.7 mm greater
on each side of the mandibular arch than
their permanent successors, the canine, and
1st and 2nd premolar.
• In the maxillary arch these primary teeth are
only .9 mm larger in mesial-distal diameter.
‘Late Mesial Shift’
• The most common relationship of the 1st
permanent molars on erupting is ‘End to
End.’
• The size differential of the ‘leeway space’
between the maxillary and mandible now
permits the mandibular 1st permanent
molar to shift mesially .8 mm more than
the maxillary, and thus assume the
normal Class I molar relationship.
‘Late Mesial Shift’
• The mesial buccal cusp of the maxillary 1st
permanent molar now inter-digitates in the
buccal groove of the mandibular 1st
permanent molar. The “Class II tendency”
which has existed throughout the primary and
mixed dentitions, no longer exists.
• This forward shifting of the 1st permanent
molars is referred to as the ‘late mesial
shift.’
Overbite and Overjet
• Overbite and Overjet in the permanent
dentition are assessed as they are in
the primary dentition.
• The average degree of overbite is 3
mm and the average degree of overjet
is 3mm.
Clinical Considerations
It is commonly necessary to remove primary
molars for various reasons during the period
of the late mixed dentition. In treatment
planning, a decision must be made as to
whether a space management appliance
should be placed . One of the factors to
consider is the time anticipated between the
extraction of the primary tooth and the
emergence of the permanent successor.
Clinical Considerations
• Succedaneous teeth can be expected to
erupt when 2/3 to 3/4 of their roots are
formed. However, other factors such as
amount of bone over the tooth and history of
bone resorption due to infection must be
considered.
• A premolar tooth moves through 1 mm of
bone in approximately 4-5 months.
• When in doubt, place a space maintainer, all
other factors indicating such.
Evaluating the Occlusion in the
Mixed Dentition
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Molar Relationship
Canine Relationship
Overbite
Overjet
Adequacy of the arch circumference
Deviations from normal in tooth position
Functional disharmonies, e.g., crossbites
Chronology of the Human
Dentition
Mesio-Distal Dimensions of
Primary and Permanent
Teeth