Dental factors affecting occlusal development The final form of the occlusion and position of the teeth exhibits a wide range of variation. The main factors responsible for producing this variation can be divided into two groups, the first group containing major factors which have a general effect on the occlusion and which play a part in the development of every occlusion.General factors affecting occlusal development 1 Skeletal factors. The size, shape and relative positions of the upper and lower jaws. 2 Muscle factors. The form and function of the muscles which surround the teeth, i.e. the muscles of the lips, cheeks and tongue. 3 Dental factors. The size of the dentition in relation to the size of the jaws. The size of the dentition in relation to jaw size The third major factor affecting the development of the occlusion of the teeth is the relationship between the size of the dentition and the size of the jaws which have to accommodate the teeth. Ideally, there should be adequate space for the teeth to erupt into the mouth without crowding or overlap. In the primary dentition, actual overlapping of the teeth is unusual, and a disproportion between jaw size and tooth size is usually manifested as a lack of spacing rather than as actual crowding.In the permanent dentition, however, crowding of the teeth is much more common. The etiology of dental arch crowding has been the subject of several theories. It has been suggested that there is an evolutionary trend towards a diminution in size of the jaws without a corresponding diminution in tooth dimensions. It has also been suggested that dietary factors may be involved, the modern diet needing less chewing and therefore providing less stimulus to jaw growth than the more primitive diets. There is little evidence to support this theory. A further theory postulates that present-day populations represent a mixture of peoples from various ethnic backgrounds, and such interbreeding of people with different physical characteristics leads to skeletal and dental disharmonies.

1. Dental factors affecting
occlusal development
ACHIEVED BY: Dr.Maen Dawodi

2. The final form of the occlusion and position of the teeth exhibits a
wide range of variation.
The main factors responsible for producing this variation can be
divided into two groups, the first group containing major factors
which have a general effect on the occlusion and which play a part in
the development of every occlusion.
General factors affecting occlusal development
1 Skeletal factors. The size, shape and relative positions of the upper
and lower jaws.
2 Muscle factors. The form and function of the muscles which
surround the teeth, i.e. the muscles of the lips, cheeks and tongue.
3 Dental factors. The size of the dentition in relation to the size of the
jaws.

3. The size of the dentition in relation to jaw size
The third major factor affecting the development of the
occlusion of the teeth is the relationship between the size of
the dentition and the size of the jaws which have to
accommodate the teeth. Ideally, there should be adequate
space for the teeth to erupt into the mouth without crowding
or overlap.
In the primary dentition, actual overlapping of the teeth is
unusual, and a disproportion between jaw size and tooth size is
usually manifested as a lack of spacing rather than as actual
crowding.
In the permanent dentition, however, crowding of the teeth is
much more common.

4. The etiology of dental arch crowding has been the subject of
several theories. It has been suggested that there is an
evolutionary trend towards a diminution in size of the jaws
without a corresponding diminution in tooth dimensions.
It has also been suggested that dietary factors may be involved,
the modern diet needing less chewing and therefore providing
less stimulus to jaw growth than the more primitive diets.
There is little evidence to support this theory. A further theory
postulates that present-day populations represent a mixture of
peoples from various ethnic backgrounds, and such
interbreeding of people with different physical characteristics
leads to skeletal and dental disharmonies.

5. It must be remembered that disproportions in dentition size
and jaw size do not always manifest as dental arch crowding.
The form and size of the dental arch is important in governing
the space available for the teeth, and the size of the dental arch
may not be the same as the size of the arch of the basal bone
of the jaw. Skeletal relationship and muscular factors can
produce a dental arch which is larger or smaller than the arch
of the basal bone, thus reducing or increasing the effects of
excessive dentition size. Therefore, in considering these effects,
it is more realistic to consider dentition size in relation to
dental arch size, rather than to jaw size.

6. The effects of excessive dentition size
Excessive dentition size in relation to dental arch size can have
the following effects:
1 Overlapping and displacement of teeth.
2 Impaction of teeth.
3 Space closure after extractions.

7. OVERLAPPING AND DISPLACEMENT OF TEETH
When the dental arch is too small for the dentition, teeth
erupting into the arch tend to become displaced by teeth
already in the arch. This particularly affects the last teeth to
erupt in any group, the lateral incisors, second premolars,
canines and third molars. In the incisor region, the teeth tend
to overlap, a condition often called imbrication, though
imbrication strictly refers to overlapping like tiles, i.e. all in the
same direction. In the buccal segments, the teeth tend to be
displaced out of the arch.
IMPACTION OF TEETH
Impaction of teeth occurs when eruption is completely blocked
by other teeth due to crowding. Again, it tends to affect the last
teeth to erupt in each segment .

8. SPACE CLOSURE AFTER EXTRACTIONS
There have been many investigation into spontaneous space
closure after extraction of teeth. Seipel (1946) found that in the
primary dentition space closure occurred less in the incisor
region than in the molar region, and more in the upper arch
than in the lower. He also found that in the primary dentition,
space closure after extractions was progressive up to 28
months after the extractions, but in the permanent dentition
space closure proceeded most rapidly for the first 3 months,
slowed a little up to 9 months, and then slowed considerably,
with little space closure thereafter. He found that the most
important factor in governing the amount and rate of space
closure was the degree of crowding of the dental arch, a finding
that has been confirmed by most investigators. It is fairly
generally accepted that space closure is dependent mainly on
the relationship between dental arch size and dentition size.

9. The effects of early loss of primary teeth
These effects can be considered under the following headings:
1 Function and oral health.
2 Over-eruption of opposing teeth.
3 Psychological effects on child and parent.
4 Position of permanent teeth.

10. EFFECTS ON THE POSITION OF PERMANENT
TEETH
As far as the occlusion and position of the teeth is concerned, the
most important result of premature loss of primary teeth is space
closure, but this does not mean that premature loss is necessarily
a disadvantage to the ensuing occlusion. The movement of teeth
which will occur in potentially crowded jaws may even prove
advantageous, by localizing the crowding to one part of the
dental arch instead of allowing it to be spread around the arch.

11. From a consideration of the factors involved in space closure,
the following categories of conditions can be outlined, in which
premature loss of primary teeth may have adverse effect or no
adverse effect on the position of the permanent teeth.
(a) When there is ample space in the dental arch to
accommodate all the successional teeth, little or no space will
be lost by spontaneous movement following loss of primary
teeth, and no crowding of the permanent teeth is likely to
ensue.
(b) When there is just enough space for the successional teeth
to erupt without crowding, the loss of even a small amount of
space by movement of teeth into an extraction space will result
in crowding of the permanent teeth. Therefore consideration of
the ensuing occlusion must be added to other considerations in
planning the management of the primary dentition.

12. (c) When there is slight crowding potential in the dental arch
for the successional teeth it can only be relieved by the loss of
permanent teeth. It is usually desirable in this circumstance to
remove teeth symmetrically from each side of the arch.
Therefore slight crowding of the permanent teeth in one arch
would normally be corrected by the loss of two permanent
teeth from that arch.
(d) When there is severe crowding potential in the dental arch
for the successional teeth, the eventual removal of a
permanent tooth from each side of the dental arch may barely
provide sufficient space for the remaining teeth.

13. The effects of asymmetric loss of primary teeth
In a crowded arch, if the loss of primary teeth occurs only on
one side of the arch the resultant distal movement of teeth
anterior to the extraction space can lead to an asymmetry of
the dental arch, with deviation of the centre, which can be
difficult to treat. Therefore, in a crowded arch it is best to plan
for lateral symmetry of extraction of primary teeth if any
primary teeth have to be lost .

14. The assessment of the potential space for the
teeth
It is obvious that in order to apply the above considerations to
the assessment of the effects of premature loss of primary
teeth it is necessary to be able to assess the potential space
available for the successional teeth. This involves assessment
of both the space available in the dental arches and the size of
the successional dentition. The first can be readily assessed by
observation or direct measurement. The second is more
difficult, since the teeth are unerupted.
Two methods of assessment are commonly used, direct
observation and mixed dentition analysis.

15. MIXED DENTITION ANALYSIS
A more accurate assessment of the potential spacing condition
of the permanent successional teeth can be made by using
some form of mixed dentition analysis. At its simplest, this
involves measurement of the space available for permanent
canines and premolars and radiographic measurement of the
size of the unerupted teeth.

16. Space maintenance
Space maintenance by preservation of primary teeth or by
removable or fixed space maintainers, should be considered if
space loss is likely and is undesirable. Oral health problems
may arise from the long-term use of artificial space
maintainers.

17. Thank you