Aetiology of malocclusion

Question 1

What are Andrew’s six keys?

Answer 1

Crown angulation (tip)
Molar relationships
Rotations
Contact points/spacing
Curve of spee
Crown inclination (torque)

Question 2

Name some aetiologys of skeletal relationships

Answer 2

Question 3

When do we accept the skeletal pattern or modify it?

Answer 3

This is dependent on a number of factors, the patient’s concerns, the severity of the discrepancy, their age and their motivation.

Question 4

What are the soft tissues?

Answer 4

*Lips

*Cheeks

*Tongue

*Masticatory musculature

*Periodontal Tissues

*Fraenal attachments

Question 5

What is Proffit’s equilibrium theory?

Answer 5

• The dentition erupts into a position of equilibrium with the surrounding soft tissue environment.
• Any alteration in the factors involved in equilibrium may cause an alteration in the tooth position until a new equilibrium is established.
• The forces of the tongue on the inside of the teeth and lips and cheeks on the outside of the teeth are balanced. When we carry out orthodontic treatment we apply forces to the teeth which changes the equilibrium and the teeth move.
• It states that the duration of any applied force is more important than the magnitude of the force. Meaning that if we move teeth out of equilibrium zone, then the lighter but longer duration forces will result in the teeth moving back, and relapse is a strong possibility.

Question 6

What do we assess orthodontically when looking at a patients lips?

Answer 6

*Resting lip line – vertical position- are they acting higher or lower on the upper incisors?

*Lip competence – the ability to get a lip seal, does the patient strain to achieve competence?

*Growth of the lips - how old is the patient, are they going to grow more?

*Lower lip trap - discussed in more detail in Class II div I cases

*Lip contour - are they thin, are they full?,is one thicker than the other?

*Ideal occlusion - resting lower lip covers between a third and a half of the labial surface of the upper central incisors in the A-P and vertical position to aid stability (Ballard 1967)

Question 7

What are the average lip lengths? (M&F)

Answer 7

*20mm female

*22mm male

Question 8

How does lip competence change with age?

Answer 8

It improves with age

Question 9

When is the majority of lip growth?

Answer 9

Through pubertal spurt
9 – 13yrs in females *9 – 15yrs in males

Question 10

What can a large tongue cause in terms of malocclusions?

Answer 10

Procline lower incisors and may also result in spacing.
Retracting the incisors will encroach on tongue’s space and they will be in an unstable position.

Question 11

What is an endogenous tongue thrust? Aetiology?

Answer 11

Swallowing activity accompanied by a thrusting behaviour

Very Rare (~1%)

? in-built neuromuscular defect e.g. cerebal palsy, Down’s syndrome.

Question 12

Name some features of endogenous tongue thrust

Answer 12

*Bimaxillary proclination

*Tongue thrust associated with lip incompetence or only very mild incompetence

*Presence of a large part of the tongue between the teeth at all times

*Reversed curve of Spee in both arches

*A marked lisp

Question 13

State the percentages of digit sucking in a) infancy and b) 12 years

Answer 13

In infancy, up to 50% may have a sucking habit

At age 12 years, 2% of the population have the habit

Question 14

How does the habit of digit sucking alter dentition/soft tissues?

Answer 14

The habit alters the intrinsic soft tissue pressures, this alters the forces which were in equilibrium and tooth position may alter.

1. Proclination of upper incisors
2. Retroclination of lower incisors
3. AOB
   -Differential eruption of teeth
   -AOB may be asymmetric
4. Maxillary constriction
   -Lower tongue position
   -Increased buccinator activity
   -Potential unilateral crossbite

Question 15

Name some dental factors of malocclusion

Answer 15

*Variations in tooth number

*Abnormalities in tooth position

*Abnormalities in tooth form

Question 16

What is dentoalveolar disproportion

Answer 16

Occurs where there is a discrepancy between the size and/or number of the teeth, and the size of the dental arches, or the space within that arch to accommodate the teeth, resulting in crowding or spacing

Question 17

Name some aetiology’s of crowding

Answer 17

*Size of the teeth

• Number of the teeth
• Position of the teeth
• Reduced size of dental arch

Insufficient space within an arch:

• Retained primary teeth or early loss of primary teeth

Question 18

What is hypodontia

Answer 18

The developmental absence of one or more teeth (excluding 3rd molars)

Question 19

What is oligodontia?

Answer 19

Absence of 6 or more teeth

Question 20

What is anodontia?

Answer 20

Absence of all teeth

Question 21

Name the incidences of hypodontia

Answer 21

<1% primary dentition

*4-6% permanent dentition (Polder 2004)

*2% 2s - May be associated with ectopic 3s

*3% all 5s

Question 22

What is the aetiology of hypodontia?

Answer 22

Hypodontia is associated with the environment; however, the majority of cases are thought to be genetic with a familial pattern. This is under extensive research.

Question 23

Name some syndromic associations of hypodontia

Answer 23

Ectodermal dysplasia – X link recessive, affects the skin, sweat glands, nails, teeth.

Cleft lip and palate

Down Syndrome

Holoprosencephaly – solitary midline maxillary central incisor, facial clefts, Cyclopia, autosomal recessive

Question 24

What are some local factors of hypodontia?

Answer 24

● Irradiation of the jaws in early life.

●Microdontia associated with chemotherapy.

Question 25

How is hypodontia managed?

Answer 25

Multidisciplinary clinics - Paediatric, Restorative and Orthodontics

Simple cases can be managed in specialist practice with the GDP providing the restorative care.

Question 26

What are supernumerary teeth?

Answer 26

A tooth that has developed in addition to the normal series of teeth.

Question 27

What is the aetiology/associations of supernumerary teeth?

Answer 27

Aetiology: unknown, however, theories include an offshoot of the dental lamina or the development of a tertiary dentition.

*Some craniofacial syndromes are associated with an increased incidence of supernumerary teeth: Cleft lip and palate, Cleido-cranial dysostosis, Gardner syndrome.

Question 28

What is the incidence of supernumerary teeth?

Answer 28

3% of the Caucasian population in the permanent dentition

In the primary dentition, the incidence < 1%.

M: F 2:1

Maxilla : Mandible 5:1

Question 29

What are the classifications of supernumerary teeth?

Answer 29

Supplemental, Conical, Tuberculate, Odontome

Question 30

Name the characteristics, incidence and management of supplemental numerary teeth

Answer 30

Duplication of a tooth within a series

*Found erupted distal to the last standing tooth in that series.

*Usually erupt, causing crowding.

Incidence: 7% of supernumeraries

Management: depends on the malocclusion, will be managed often in a joint clinic with paeds/restorative and orthodontics

Question 31

Name the characteristics, incidence and management of conical numerary teeth

Answer 31

*Small peg-shaped tooth, often occurring in the maxillary midline (mesiodens), and often erupt.

*If they erupt into the line of the arch, they can cause crowding.

Incidence: 75% of supernumeraries

Management: if erupted extract with GDP, if unerupted and no clinical reason to remove then monitor

Question 32

Name the characteristics, incidence and management of tuberculate numerary teeth

Answer 32

*‘Barrel-shaped’; lack of root development

*Often occur in pairs, most commonly palatal to the maxillary incisors, preventing their eruption.

*Can indirectly contribute to development of a malocclusion.

*If adjacent teeth drift into the space, can result in crowding of the unerupted tooth.

Incidence: 12% of supernumeraries

Management: depends on its effect on the dentition

• removal, maintain space, expose & bond of impacted central incisor if indicated

Question 33

Name the two kinds of odontome numerary teeth

Answer 33

Complex: haphazard arrangement of dental tissue most commonly anterior maxilla

Compound: discrete tooth like structures (denticles) usually located in the premolar/ molar region x4 more common than complex odontomes