Etiology of malocclusion Flashcards
Predisposing Factors to Malocclusion
(4)
*Disturbances in Embryologic Development
*Heredity (genetics)
*Functional matrix
*Traumas
*Functional matrix
(2)
*Muscular or functional disturbances
*Habits
*Traumas
(1)
*Especially mandibular fractures.
Normal skeletal relationship
* — as a reference
* Position and projection of the
upper jaw
* Position and projection of the lower
jaw
Cranial base
Types of malocclusion
* Malocclusion occurs in – dimensions
* Angle classification is based on – relationships
3
AP
Normal Occlusion:
Class 1 Malocclusion:
Class 2 Malocclusion:
Class 3 Malocclusion:
30%
50-55%
15%
1-4%
maxillary prognathism=
class 2
mandibular prognathism=
class 3
Class II
(3)
- Mandibular retrognathism
- 40% present bimaxillary retrusion
- Rarely true maxillary prognathism
Typical Skeletal class II
(4)
- Mandibular retrognathism
- Proclined upper incisors
- Deep bite
- However, multiple presentations are
possible
Cl I maloccusion
(2)
- Jaws are well aligned in the anteroposterior
dimension - Vertical and transverse dimensions are
variable.
Transverse dimension
(3)
Intermolar distance
Intercanine distance
Arch shape:
* Upper:
* Lower:
Class III
malocclusion
(4)
- Maxillary Retrognathism
- Mandibular prognatjism
- Usually a combination of the two conditions
- Vertical dimension is variable Deepbite to openbite
Prevalence of Class III malocclusions
* Depends on the population
* Southeast Asian ~
* Middle eastern ~
* Indian ~
* European ~
15%
10%
1%
1-4%
Genetics of Class III
* Focused on
mandibular prognathism
Genetics of Class III
* Family and twin studies
* Suggest a
polygenic model as primary cause of Class III malocclusion
Genetics of Class III
* Linkage Analysis studies
* Used to determine the
chromosome loci associated
with the condition
* Suggested loci: 1p22, 1p36,
3q26.2, 6q25, 11q22, 12q13,
12q23, 19p32.2
18
Openbite: Multifactorial Etiologies
(4)
- Transitory
- Skeletal (genetic)
- Neuromuscular
imbalance (CP) - Combination
Sleep Apnea
- Neuromuscular
imbalance (CP)
(2)
- Oral habits
- Anterior tongue
posture
Deep bite
(3)
*Skeletal
*Overeruption of incisors
*Undereruption of molars
Transverse dimension
(3)
*Usually maxillary transverse
deficiency
*Maybe caused by overdeveloped
mandible
*Some are also caused by
unfavorable dental angulations
Disturbances of Dental Development
(5)
- Congenitally missing teeth
- Malformed and supernumerary teeth
- Interference with eruption
- Ectopic eruption
- Early loss of primary teeth
- Congenitally Missing Teeth
(2)
*Anodontia (very rare)
*Oligodontia (several teeth missing)
Dr Moyers’ Explanations for Congenitally
Missing Teeth
(5)
- Heredity
- Ectodermal Dysplasia
- Localised inflammations or infections
- Systemic conditions, e.g. ricketts
- Evolutionary changes in the dentition (specially third molars)
Ectodermal dysplasia
(2)
*Oligodontia
*Poorly shaped teeth
Most frequently missing teeth
(3)
*Upper lateral incisors
*Lower second premolars
*Lower central incisor
- Malformed Teeth
(3)
*“Peg” maxillary lateral incisors
*Crown can be mishaped
*Root may be shortened
Mesio Distal Size of the Dentition
(2)
- Proportionality of tooth sizes within a dentition
- Bolton ratio
Bolton Ratio
OVERALL RATIO:
sigma Mandibular 6-6 (mm) /
sigma Maxillary 6-6 (mm)
Bolton Ratio
ANTERIOR RATIO:
sigma Mandibular 3-3 (mm) /
sigma Maxillary 3-3 (mm)
In order to develop a proper overbite and
overjet, the size of the lower dentition
must be proportional to the size of the
upper dentition
*This proportion is called the
Bolton ratio.
Supernumerary Teeth
(1)
*Mesiodens
