Etiology of Malocclusions Part 1 Flashcards
What are the predisposing factors to malocclusion?
- Disturbances in Embryologic Development (defects that happen during gestation)
— Heredity (genetics) (genes from all generations back from both sides - father and mother) - Functional matrix
— Muscular or functional disturbances
— Habits - Traumas
— Especially mandibular fractures (very common to see condylar neck fracture on kids)
How do you determine skeletal relationship?
- Cranial base as a reference
— Position and projection of the upper jaw
— Position and projection of the lower jaw
Malocclusion occurs in ___ dimensions
3
(angles classification is in AP - sagittal relationship)
__% of patients have normal occlusion
30%
- class 1 molar relationship (wouldn’t benefit from ortho tx)
____% of patients have class I malocclusion
50-55%
(molar relationship is class I but the remaining teeth are misaligned)
___% of patients have class II malocclusion
15%
(can have vertical and/or buccal/lingual problems as well)
- in an ortho practice about 25-40% of pts have a class II malocclusion (one thing that we see in clinic, another what the general public has; this is the difference between incidence and prevalence
incidence - general population
prevalence - incidence in a specific group of subjects)
___% of patients have class III malocclusion
1-4%
What skeletal class is a jaw without prognathism?
class I
- usually aligned
What skeletal class is a jaw with maxillary prognathism?
class II
- retrusive mandible, protrusive maxilla
What skeletal class is a jaw mandibular prognathism?
class III
- protrusive mandible
What are the possible jaw positions of class II malocclusions?
- Mandibular retrognathism (cause of it)
- 40% present bimaxillary retrusion (both maxilla and mandible are slightly retrusive)
- Rarely true maxillary prognathism
What does a typical skeletal class II look like?
- Mandibular retrognathism
- Proclined upper incisors
- Deep bite
How are the jaws positioned in a class I malocclusion?
- Jaws are well aligned in the anteroposterior dimension
- Vertical (sagittal dimension) and transverse dimensions are variable
What distances are measured in the transverse dimension?
Intermolar distance
Intercanine distance
Should the maxillary intermolar distance be the same, greater, or lesser than on the mandibular?
the same
they should be equal
Both arches (max and mand) should have the same…
arch form/shape
What are the possible jaw positions of class III malocclusions?
- Maxillary Retrognathism
- Mandibular prognathism
- Usually, a combination of the two conditions
- Vertical dimension is variable… Deep bite to open bite
What is the prevalence of class III malocclusions by ethnicity?
Depends on the population
*Southeast Asian ~15% of population
*Middle eastern ~10%
*Indian ~1%
*European ~1-4%
Fundamentally, mandibular growth is induced by both _________________ mechanisms, which interact with each other to produce a Class III phenotype
genetic and environmental
What contributes to an openbite?
- Transitory
- Skeletal (genetic)
- Neuromuscular imbalance (CP)
— Oral habits
— Anterior tongue posture - Combination Sleep Apnea
What factors can create a malocclusion?
Genetic
Environmental
Other factors
How do you assess a skeletal malocclusion?
Lateral cephalogram
What is the intuitive theory?
Sometimes can look at face and see problems of SKELETAL ORIGIN
What is the most difficult malocclusion to treat?
Class III malocclusion with open bite
