Aetiology of Malocclusion Flashcards
What are the four components of facial skeleton ?
Maxilla base.
Mandibular base.
Alveolar processes of upper and lower.
Maxillary complex (attached to anterior skull base).
Mandibular complex (attached to posterior skull base).
What malocclusion is most commonly associated with genetic aetiology ?
Class III malocclusion.
What are 3 examples of environmental etiological factors affecting malocclusions ?
Muscles of mastication.
Mouth breathing.
Head posture.
Describe a Class I malocclusion.
Mandible related normally to maxilla so teeth erupt into normal occlusion. Jaws are normally the correct size.
Describe a Class II malocclusion.
Mandible placed posteriorly relative to maxilla.
What can be the anatomical reasons for a Class II malocclusion ?
Mandible too small - most common.
Maxilla too large.
Obtuse cranial base angle - normal mandible but set far back in skull base.
Describe a Class III malocclusion.
Mandible placed anteriorly relative to maxilla.
What can be the anatomical reasons for a Class III malocclusion ?
Maxilla too small - most common.
Mandible too large.
Acute cranial base angle - with normal jaw size.
What is dental alveolar compensation ?
Forces from lips, cheeks, tongue incline teeth towards position of soft tissue balance - leads to disguising of malocclusion with soft tissue envelope.
What is a lateral cephalogram ?
Standardised (reproducible) lateral radiograph of face and skull base.
What makes a lateral cephalogram reproducible ?
Patient at set distance from cephalostat between cone and film.
When would a cephalogram be beneficial in orthodontic treatment ?
Monitoring growth.
Severe malocclusions.
What does the SNA angle show ?
Relationship of maxilla to anterior cranial base.
What does the SNB angle show ?
Relationship of mandible to anterior cranial base.
What does the ANB angle show ?
Relationship of maxilla to mandible.
How is the SNA angle measured ?
Angle between lines -
- Between sella turcica and nasion.
- Between nasion and maximum concavity of upper incisors.
How is the SNB angle measured ?
Angle between lines -
- Between sella turcica and nasion.
- Between nasion and maximum concavity of lower incisors.
How is the ANB angle measured ?
Difference between upper and lower maximum concavity lines.
What is the normal SNA angle for a Class I malocclusion ?
81 degrees (+/- 3 degrees).
What is the normal SNB angle for a Class I malocclusion ?
78 degrees (+/- 3 degrees).
What is the normal ANB angle for a Class I malocclusion ?
3 degrees (+/- 2 degrees).
If the maxilla is prognathic in a Class II malocclusion, will the SNA angle be increased or decreased compared to the standard values ?
Increased.
If the mandible is prognathic in a Class III malocclusion, will the SNA angle be increased or decreased compared to the standard values ?
Decreased.
What value will ANB angle be in a Class II malocclusion ?
> 5 degrees.
What value will ANB angle be in a Class III malocclusion ?
<1 (-) degrees.
What is the Frankfort plane measured between ?
Lower orbital rim to superior border of external auditory meatus.
What is the mandibular plane measured against ?
Lower border of mandible.
Where should mandibular and Frankfort plane meet ?
External occipital protuberence.
What angle can be measured between mandibular and Frankfort plane ?
Frankfort-mandibular plane angle - FMPA.
What two anatomical features is upper anterior face height measured between ?
Glabella to base of the nose.
What two anatomical features is lower anterior face height measured between ?
Subnasale to soft tissue menton.
What is the average ratio between LAFH and UAFH ?
LAFH - 55%
UAFH - 45%
In a patient with an anterior open bite, what will FMPA and LAFH values be vs. normal values ?
Increased FMPA.
Increased LAFH.
What are five causes for transverse relationship variation ?
Arch discrepancies.
Mandibular displacement.
Transverse dento-alveolar discrepancy.
Facial asymetry.
Arch size discrepancy.
What is an example of arch discrepancies ?
Unilateral or bilateral crossbite.
What causes mandibular displacement ?
Inter-arch width discrepancy causing upper and lower posterior teeth to meet cusp to cusp. Mandible has to deviate to gain ICP.
What are 3 examples of true facial asymmetries i.e. not to do with tooth position ?
Condylar hyperplasia.
Hemi-mandibular hyperplasia or elongation.
What are the four causes of malocclusion ?
Skeletal pattern.
Dental.
Soft tissue.
Other i.e. habits.
What is the definition of local causes of malocclusion ?
Localised problem or abnormality within either arch, usually confined to 1/2 or several teeth producing malocclusion which tends to get worst with time.
What are 5 local causes of malocclusion ?
Variation in tooth number.
Variation in tooth size or form.
Abnormalities of tooth position.
Local abnormalities of soft tissues.
Local pathologies.
What is the definition of hypodontia ?
Developmental absence of one or more teeth.
Is hypodontia more common in males vs. females ?
Females - 3:2.
What teeth are most commonly affected by hypodontia ?
Upper laterals and second premolars.
What is the definition of retained primary teeth ?
A difference of more than 6 months between shedding of contra-lateral teeth - disruption in sequence of eruption.
What are the five reasons which a primary tooth may be retained ?
Absent successor.
Ectopic successor or dilacerated.
Infra-occluded (ankylosed) primary molars.
Dentally delayed in terms of development.
Pathology/supernumerary.
What are two treatment options for retained primary teeth ?
- Maintain primary tooth as long as possible if good prognosis.
- XLA deciduous tooth really to encourage spontaneous space closure in crowded cases.
What is the definition of infra-occluded primary molars ?
Process where tooth fails to achieve or maintain its occlusal relationship with adjacent teeth.
Can be measured slight (<2mm from occlusal surface), moderate (inter-proximal contact) and severe (below inter-proximal).
What are 4 causes for early loss of primary teeth ?
Trauma.
PA pathology.
Caries.
Resorption of successor.
What is a balancing extraction ?
Extraction tooth from the opposite side of same arch - designed to minimise midline shift.
What is a compensating extraction ?
Extraction of tooth from opposing arch of the same side - designed to maintain occlusal relationship.
What is the impact of early loss of primary canines ?
Unilateral loss in crowded arch - causes midline shift.
Consider balancing extraction.
What teeth are most commonly ectopic ?
8s, 3s, 6s, 1s.
From what age should ectopic maxillary canines be palpated to check position ?
9+ years old.
What % of ectopic canines are palatally placed ?
80%
What can be 4 signs of ectopic canines in clinical assessment ?
Visualisation/palpation of obvious bumps of 3.
Inclination of 2.
Mobility of c or 2.
Colour of c or 2.
What 2 radiographs are required for radiographic assessment of ectopic canines ?
OPT and upper anterior oblique occlusal.
Use parallax technique.
What are the 3Ps in assessment of ectopic canines ?
Presence, position, pathology.
For are six management options of ectopic canines ?
- Prevention.
- Extraction of c to encourage improvement in position of 3 - interceptive orthodontic treatment.
- Retain 3s and observe - accept position.
- Surgical exposure and orthodontic alignment.
- Surgical extraction.
- Autotransplantation.
