Etiology of Malocclusion 1 Flashcards
What are the 3 tissue types that we need to consider when thinking of malocclusions
skeletal
muscular
dentoalveolar
What are the general skeletal etiological factors
size, shape, relative positions of the upper and lower jaws
What are the general muscular etiological factors
form and function of the muscles that surround the teeth i.e lips, cheeks and tongue
What are the general dentoalveolar aetiolgoical factors
size of the teeth in relation to the size of the jaws
What are the components of the facial skeleton
maxillary & mandibular bases
maxillary and mandibular alveolar processes (carry teeth)
What is the maxillary complex attached to
anterior cranial base
What is the mandibular complex articulating with
glenoid fossa of the posterior cranial base
What does facial variation result in
differences in the size, shape of the maxilla, mandibular and alveolar processes and their relationship to each other in all 3 planes of space
variation in the size and angle of the cranial base causing a difference in the relative position of the mandible
What does malocclusion result from
disharmony between the components of the facial skeleton
What are the 3 planes that facial variation can occur
antero-posterior
vertical
transverse
What is the etiology of skeletal variation
genetic and environmental factors
What features of malocclusion are hereditary
class 3
What are possible environmental factors that can result in malocclusion
masticatory muscles
mouth breathing
head posture
What is a class 1 antero-posterior relationship
mandible related normally to maxilla such the teeth erupt into class 1 occlusion jaws usually correctly sized but may have bimaxillary protrusion or recursion
What is the normal cranial base angle
130-135 degrees
What is lateral cephalometry
standardized lateral radiographs of the face and base of the skull
reproducible - patient is positioned in a cephalostat a set distance from the one and the film
What is cephalometry
analysis and interpretation of these radiographs
What is the radiographic technique
ALARA - soft tissue filter thyroid collar triangular collimation rare earth screen lanes screen fastest film possible
How is cephalometry analysis done
hand traced onto paper
digitized using a computer
What is the SNA
relates maxilla to anterior cranial base
What is the SNB
relates mandible to anterior cranial base
What is the ANB
relates mandible to maxilla
In class 1 what is the SNA
avg 81 degrees
In class 1 what is the SNB
avg 78
In class 1 what is the ANB
avg 3
What is the class II antero-posterior relationship
mandible placed posteriorly relative to maxilla teeth erupt into post-normal class II occlusion
What are causes of class II
mandible too small (most commonly) or maxilla too large or combo
mandible normally sized but placed too far back due to obtuse cranial base angle
What is the SNA in class II
usually average but may be increased if the maxilla is prognathic
What is the SNB in class II
usually decreased as mandible is further back
What is the ANB in class II
> 5 so outside of the standard deviation
What is a class III anterior posterior relationship
mandible placed anteriorly relative to maxilla
tooth rust into pre-normal occlusion (class III)
What is the cause of class III
maxilla is too smalll (most commonly, mandible is too large or combination of both
normally sized jaws but mandible positioned too far forward due to acute cranial base angle
What is the SNA in class III
decreased if maxilla is deficient
What is the SNB in class III
often average but may be increased if mandible is prognathic
What is the ANB
<1 or negative
What is dentoalveoalr compensation
the dents-alveolar structures underlying discrepancy
forces from the lips, cheeks and tongue tend to incline teeth towards a position of soft tissue balance
What are the clinical values we look at when looking at the vertical jaw relationship
Frankfurt and mandibular plane
the two normally meet at the external occipital protuberance
What is the frankfurt plane
lower orbital rim to superior border of external auditory meatus
What is the mandibular plane
lower border of the mandible
What is the upper anterior face height
brow ridge (glabella) to base of nose
What is the lower anterior face height
base of nose (sub nasal) to inferior aspect of the chin
What is the average ratio of LAFH to TAFH
50%
What is the average value of FMPA
27 degrees
On a lateral ceph where is the frankfurt plane
(orbitale to porion)
On a lateral ceph where is the mandibular plane
(menton to gonion)
What is the upper anterior face height on the lateral ceph
nasion to anterior nasal spine
What is the lateral anterior faec height on the lateral ceph
anterior nasal spine to mention
What is the average value of LAFH to TAFH
55%
What is the LAFH to TAFH proportion for a long facial type
> 55%
What is the FMPA for a long facial type
<31 degrees
What is a long facial type
steeply inclined mandibular plane
backward mandible growth rotation
anterior open bite tendency
What is a short facial type
tendency to parallelism of jaws
forward mandibular growth rotation
deep overbite tendency
What is the LAFH to TAFH proportion in short facial type
<55%
What is the TAFH proportion in in short facial type
<23 degrees
What can arch width discrepancies (transverse) result from
disproportion of maxillary and mandibular dental arches
causes unilateral or bilateral buccal segment cross bitse
often exaggerated by anteroposterior discrepancies
How does mandibular displacement occur
occurs where inter-arch width discrepancy causes upper and lower posterior teeth to meet cusp to cusp
mandible forced to deviate to one side to achieve position of inter-cuspation
possible association with TMD
What are dental causes of facial asymmetries
displacement of normal mandible due to unilateral cross bite
What is a true mandibular asymmetry
hemi mandibular hyperplasia/elongation
condylar hyperplasia
What is dentoalveolar disproportion
discrepancy between size of teeth and jaws
What is crowding caused by
small jaws and normally sized teeth
large teeth - macrodontia
What is spacing caused by
large jaws, normally sized teeth small teeth (microdontia)
