Introduction to Orthodontics Fifth Year

1. Seventh Lecture
Etiology of
Malocclusion

2. Angle’s classification
Class I malocclusion:
Lower dental arch is in normal anteroposterior relation to
upper dental arch as evidenced by occlusion of mesiobuccal
cusps of upper first permanent molars in buccal groove of
the lower first permanent molars.
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3. In Angle’s Class I, mesiodistal relationship of
first molars are normal, but malocclusion exists into
one or more of the following three categories:
A. Local abnormalities:
1. Crowding of upper and lower incisors.
2. labial inclination of anterior teeth.
3. Anterior cross bite.
4. Posterior cross bite.
5. Local abnormalities due to premature
loss of decid. molars with loss of space in
the premolar region.
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5. B. Vertical malrelationship:
May be either deep or deficient overbite.
C. Disproportion in size between basal bone
and teeth:
Basal bone may be either too large
resulting in spacing or too small resulting in
crowding of upper and lower teeth &
impactions of third molars.
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6. Class II malocclusion:
Lower dental arch is in distal relation to
upper dental arch as evidenced by occlusion of
mesiobuccal cusp of the upper first permanent
molar in the embrasure between lower first
permanent molar and lower second premolar.
It is measured in terms of units i.e. width of one premolar is
considered one unit (or ½ width of one molar).
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7. There are two divisions of Class II. They are affecting bilaterally
the dental arch.
Division 1: This is usually characterized by:
1. The upper incisors are proclined.
2. Increased overjet.
3. There is often short upper lip with failure in anterior lip seal.
4. V-shaped upper arch i.e. narrow in the canine and premolar
region and broadening between the molars.
5. The mandible may be deficient and chin underdeveloped.
Class II div.1
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8. Division 2: This is usually characterized by:
1. The upper central incisors show lingual inclination & may be
overlapped by the upper lateral incisors.
2. The upper arch is usually broad.
3. Deep incisor overbite, both upper & lower incisors are in
apparent supra-occlusion.
4. The upper lip is of normal length and contacts the lower lip
with deep mental groove below lower lip.
5. The mandible is frequently of good size.
Class II div. 2
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9. Comparison between Class II div. 1 & div. 2
Feature
Division 1
1.Upper incisors Proclinated
2. Upper arch
3. Upper lip
V-shape
Short – failure of
lip seal
4. Mandible
Deficient chinunderdeveloped
5. Overbite
Deep, lower
incisors near palatal
mucosa
6. Angle’s Class Class II
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Division 2
Retroclined central
incisors &
overlapped with
lateral incisors
Broad
Normal length
Good size
Deep, upper &
Lower incisors in
supraocclusion
Class II
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10. Class III malocclusion:
Lower dental arch is in mesial relation to
upper dental arch as evidenced by occlusion
of mesiobuccal cusp of upper first permanent
molar in the embrasure between lower first &
second permanent molars.
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11. General Causes
Local Causes
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12. A. General Causes
1. Evolution:
In the evolutionary scale, there is
gradual reduction of jaw sizes, so
crowding of teeth and impacted
wisdoms become more common.
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13. A. General Causes
2. Congenital malformation:
Congenital
malformation
Environmental
Hereditary
Chromosomal
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Genetic
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14. A. General Causes
2. Congenital malformation:
Definition:
Defects occur during intrauterine life
and detected at birth or during
infancy, Congenital malformations
may be due to:
i. Environmental causes:
a. Infective agents e.g. viruses
(German measles)
b. Exposure to radiation
Repaired Cleft
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15. A. General Causes
2. Congenital malformation:
i. Environmental causes:
c. Drugs with teratogenic effects
d. Hormones
e. Nutritional disorder
f. Smoking, alcohols & caffeine
g. Maternal defects
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16. A. General Causes
2. Congenital malformation:
ii. Hereditary causes:
– Chromosomal
– Genetic
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17. ii. Hereditary causes
A. General Causes
2. Congenital malformation:
a. Chromosomal abnormalities:
e.g. Trisomy 21(Down’s Syndrome) or
mongolism:
Mental retardation, flat nasal bridge,
fissured protruding tongue &
macroglossia.
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18. A. General Causes
2. Congenital malformation:
b.Genetic: due to defective genes,
there will be:
- Achondroplasia
- Cleidocranial dysostosis:
Retarded eruption of permanent
teeth, Short & thin roots of
permanent teeth, supernumerary
teeth.
- Mandibulofacial dysostosis.
- Dentinogenesis imperfecta.
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Cleidocranial dysostosis
Achondroplasia
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19. A. General Causes
3. Endocrinal
disturbances:
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20. A. General Causes
3. Endocrinal disturbances:
Hypo or hyperpituitarism: would affect
growth hormone resulting in Dwarfism,
or Gigantism /Acromegally.
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21. A. General Causes
3. Endocrinal disturbances
Hypothyroidism:
-Abnormal resorption pattern
-Retained decid. teeth
-Delayed eruption of teeth
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22. A. General Causes
4. Nutritional
deficiency:
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23. A. General Causes
4. Nutritional deficiency
Vit. D deficiency
Ricketts
(Hypocalcemia):
Hyperexcitability of
musc.(medial pterygoid musc.),
on soft bone will produce obtuse
gonial angle
open bite
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24. A. General Causes
5. Pathological
Conditions:
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25. A. General Causes
5. Pathological Conditions:
Systemic diseases that upset the developmental
time scale (e.g. eruption, resorption) might
have permanent effect. (e.g. diabetes)
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26. A. General Causes
5. Pathological Conditions:
Diseases with muscle malformation such as
atrophy, cerebral palsy have characteristic
effects on the dental arch.
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27. B. Local Causes
1. Congenital missing
teeth:
Hereditary ectodermal dysplasia
associated with partial anodontia
(Oligodontia), a dry coarse skin,
fine hair, defects of the nails and
absence of sweet glands.
Ectodermal dysplasia
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28. B. Local Causes
1. Congenital missing teeth:
The most common missing teeth are: upper &
lower third molars, upper lateral incisors, &
lower second premolars.
In case Of Missing laterals:
Maxillary canines may erupt mesially into
space of missing laterals Or may give rise to a
median diastema
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29. Causes of maxillary median diastema:
1. Physiological spacing of permanent central
incisors is normal at 7.5 years of age (Ugly Duckling
Stage) and tend to close with eruption of lateral
incisors and finally canines.
2. Familial pattern.
3. Small teeth in large jaws.
4. Missing lateral incisors.
5. Misplaced lateral incisors.
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30. Causes of maxillary median diastema:
6. Peg shaped lateral incisors.
7. Supernumerary tooth or teeth between
central incisors e.g. mesiodens.
8. Median cyst.
9. Abnormal labial frenum.
10. Imperfect fusion at midline of premaxilla.
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Dr. Ahmed Basyouni
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31. B. Local Causes
. Congenital missing teeth:
In case of Missing lower second premolar:
Deciduous second molar is usually retained, &
lower first permanent molar will be found
slightly distal to its opposing upper first
permanent molar, this is due to the larger
mesiodistal diameter of second decid. Molar
as compared to that of second premolar.
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32. Missing upper laterals & lower second premolars:
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33.  . Supernumerary
B. Local Causes
teeth:
They are commonly associated
with congenital defects as cleft
palate.
Mesiodens frequently seen near
midline palatal to upper incisors.
Removal of supernumerary teeth
allows normal teeth to erupt or
return to their correct positions
(self correction) or through
appliance therapy.
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Mesiodent
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34. B. Local Causes
2 Supernumerary teeth:
There are 4 main types:
a. Peg teeth, small conical shaped
teeth often appearing in the midline
of upp. Centrals.
b. Multicusped teeth with deep
occlusal pits
( tuberculated like premolars).
c. Supplemental teeth of normal
size and appearance.
d. Teeth of normal shape but of
larger or smaller size.
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35. B. Local Causes
2 Supernumerary teeth:
Localization of supernumerary teeth assessed as
follows:
1. Inspection & palpation.
2. Radiographs:
a. Occlusal, & periapical films
b. Method of Parallex: Two radiographs
are taken with film placed in same position each time,
but tube is moved about 4 inches, if the shadow of the
unerupted tooth moves same direction as the tube,
then it is lying palatally.
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36. Summary
General Causes
Local Causes
1.Evolution:
2. Congenital malformation:
3. Endocrinal
disturbances:
4. Nutritional
deficiency
5. Pathological Conditions:
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1. Congenital missing
teeth:
2 Supernumerary teeth:
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Lecture .
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37. March 5, 2012
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