Aetiology of Malocclusion Flashcards
what are the 3 broad aetiologies of malocclusions
Skeletal - size, shape and relative position of upper and lower jaws
Muscular - form and function of the muscles that surround the teeth e.g lips, tongue and cheeks
Dento-alveolar - size of teeth in relation to size of jaws
Cranial base angle
angle formed where the anterior cranial base and the posterior cranial base meet
Class I occlusion
‘normal occlusion’
maxilla slightly in front of mandible
lower incisors occlude or lie directly below the upper central cingulum
Class II occlusion
‘overjet’
mandible is posterior to maxilla
lower incisor edges lie posterior to the upper central cingulums
division 1 = upper incisors are proclined or normal
division 2 = upper incisors retroclined
Class III occlusion
‘reversed overjet’
mandible is anterior to the maxilla
lower incisor edges lie anterior to the upper central cingulums
dento alveolar compensation
refers to movement of dento alveolar structures to disguise skeletal discrepancies
e.g upper incisors procline and lower incisors retrocline in class IIIs making reverse overjet appear reduced
Frankfort plane
lower orbital rim to the superior border of the external acoustic meatus
mandibular plane
lower border of mandible
where do the mandibular plane and the frankfort plane usually meet (in patients with normal skeletal relationship)
external occipital protuberance
where is upper anterior face height measured from and to
glabella to base of nose
where is lower anterior face height measured from and to o
base of nose to inferior surface of chin
what is the average ratio of lower anterior face height : total anterior face height
TAFH = LAFH + UAFH (glabella to inferior border of chin)
average = 50% of TAFH
what is the average FMPA angle and what is this
frankfort mandibular plane angle
usually 27 degrees +/- 4
describe the skeletal tendencies of a ‘long facial type’
steeply inclined mandibular plane
Anterior open bite tendency
backward mandibular growth rotation
FMPA usually increased
describe the skeletal tendencies of a ‘short facial type’
parallelism of jaws
deep overbite tendency
forward mandibular growth rotation
FMPA usually decreased