Orthodontics - Atieology of Malocclusion Flashcards
what are the general aetiological factors of malocclusion?
Skeletal - size, shape and positions of the upper and lower jaws
Muscular - Form and function of muscles surrounding the teeth i.e. lips, cheeks, tongue
Dentoalveolar - Size of the teeth in relation to size of the jaw
(genetically and environmentally influenced too)
name the 3 skeletal planes.
Antero-postero
Vertical
Transverse
list the cephalometrics for a class I antero-postero relationship.
SNA relates maxilla to the anterior cranial base
Average value is 81 degrees ( +/- 3)
SNB relates mandible to the anterior cranial base
Average value is 78 degrees ( +/- 3)
ANB relates the mandible to the maxilla
Average value is 3 degrees ( +/- 2)
what causes a class II antero-postero relationship? (3)
Class II = maxilla >3mm in front
Mandible is too small (common) or maxilla is too large or both
obtuse cranial base = Mandible can be normal sized but placed too far back
list the cephalometrics for a class II antero-postero relationship.
SNA relates maxilla to the anterior cranial base
Average value is 81 degrees ( +/- 3)
For class II its usually average but can be increased if the maxilla is prognathic
SNB relates mandible to the anterior rnaial base
Value usually decreased ( < 78 degrees)
ANB relates the mandible to the maxilla
> 5 degrees (increase from average)
what causes a class III antero-postero relationship? (3)
Class III = maxilla < 2-3mm in front (behind the mandible)
Maxilla is too small (common) or mandible is too large or both
acute cranial base = Normal sized jaws but placed too far forward due to an
list the cephalometrics for a class III antero-postero relationship.
SNA = < 81 decreased if the maxilla is deficient
SNB = Value usually average (78 degrees) but can be increased if the mandible is prognathic
ANB relates the mandible to the maxilla
< 1 degrees or negative
what is dento-alveolar compensation?
where the surrounding dente-alveolar structures disguise the underlying discrepancy
name the planes used to assess the vertical jaw relationship. (2)
Frankfort plane
mandibular plane
(Both used to Create the Frankfort mandibular plane angle)
what is the average clinical value of the frankfort mandibualr plane angle?
27 degrees (+/- 4)
what is the clinical value of the frankfort mandibualr plane angle in an individual with a long face?
31 degrees
what kind of occlusion does an individual with a long face commonly have?
AOB
what is the clinical value of the frankfort mandibualr plane angle in an individual with a short face?
< 23 degrees
what kind of bite does an individual with a short face commonly have?
deep overbite (and parallelism of jaws)
what is the lower anterior face height to total anterior face height proportion in an individual with a long face?
55%
what is the lower anterior face height to total anterior face height proportion in an individual with a short face?
< 55%
when does mandibular displacement occur?
When there is inter-arch width discrepancies that cause the upper and lower cusps to meet
- mandible has to deviate to one side to avoid this
Associated with TMJ disease
what are dental causes of facial asymmetry?
Displacement of the mandible due to unilateral cross-bites
how do we measure the vertical plane?
FMPA - Frankfort mandibular plane angle
what can cause inter-arch width discrepancies, mandibular deviation and consequently unilateral posterior crossbites?
digit sucking
list the local causes of malocclusion. (5)
variation in tooth number
- supernumerary and hypodontia
variation in tooth size and from
- macrodontia and microdontia
variation in tooth position
- ectopic
abnormalities of the surrounding soft tissues
- tongue thrust, digit sucking, frenum attachments
local pathology
list the types of supernumerary teeth (4)
conical
odontome
supplementary
tuberculate
where are supernumary teeth more common?
anterior maxilla
What gender are more prone to supernumerary teeth?
males
