Aetiology of Malocclusion

Question 1

What are the 3 groups of causes of malocclusion?

What are the subtypes of each group?

Answer 1

• Genetically determined factors –> skeletal pattern, soft tissues, dentoalveolar factors.
• Environmental factors –> habits, pathology.
• Combination of both

Question 2

What are the effects of a habit on the occlusion?

Answer 2

• Proclined upper incisors.
• Retroclined lower incisors.
• AOB or reduced overbite.
• Posterior crossbones.
• Asymmetrical AOB.

Question 3

How does juvenile arthritis lead to malocclusion?

Answer 3

1. It causes resorption of the condyles.
2. Leads to condylar issues.
3. Leads to malocclusion.

Question 4

How does musculodystrophy lead to malocclusion?

Answer 4

1. It affects the soft tissues + changes the muscle balance.

2. Leads to malocclusion.

Question 5

What do the effects of thumb sucking depend on?

Answer 5

• Age of pt.
• No. of hours per day.
• Way the digit is sucked.

Question 6

What causes a class 2 skeletal pattern?

Answer 6

• Small mandible

- Mandible positioned too far posteriorly

Question 7

What causes a class 3 skeletal pattern?

Answer 7

• Retrognathic maxilla.
• Large or prognathic mandible
• Combination of both

Question 8

How does the vertical skeletal pattern influence the occlusal relationships?

Answer 8

• Increased vertical dimension = associated with AOB + incomplete overbite.
• Decreased vertical dimension = associated with deep overbite.

Question 9

How do transverse discrepancies in the skeletal pattern affect the occlusion?

Answer 9

Can result in posterior crossbones.

Narrow maxilla –> bilateral posterior cross bite.
Wide maxilla / narrow mandible –> lingual buccal cross bite (scissor bite).

Question 10

How do strap-like lower lips affect the incisors?

Answer 10

Strap-like lower lips with incompetent lips = retroclined upper incisors.

Strap-like lower lips with competent lips = proclaimed upper incisors.

Question 11

How do full, everted lips affect the occlusion?

Answer 11

Associated with bimaxillary proclination (proclination of upper + lower labial segments).

Question 12

How does a lip trap affect the occlusion?

Answer 12

1. At rest, lower lip is behind upper incisors.
2. Proclined upper incisors + retroclined lower incisors.
3. Increased overjet –> class 2 div 1.

Question 13

What is the impact of a large tongue?

Answer 13

It will cause broad arches + proclined upper teeth (because tongue pushes teeth forward).

Question 14

What are indications of a large tongue?

Answer 14

Crenations (scalloping along the lateral border).

Question 15

How does the tongue rest position influence the occlusion?

Answer 15

If the tongue is too far forward:

- Leads to bimaxillary proclination + AOB.

Question 16

What are the typical features of adenoidal facies ?

Answer 16

• Increased vertical dimension, backwards rotators.
• Narrow maxilla.
• Posterior crossbones.
• Narrow nose.
• Reduced overbite.

Question 17

How does the PDL result in malocclusion?

What are the effects?

Answer 17

• In periodontal disease, the PDL breaks down.
• Equilibrium of tooth position disturbed.
• Results in malocclusion.

Effects:

• Drifting of incisors + spacing.
• Increased overjet.
• Extrusion may occur.

Question 18

What dentoalveolar factors can cause malocclusion?

Answer 18

• Dentoalveolar disproportion (crowding + spacing).
• Developmentally missing teeth (lower 5s, upper 2s).
• Malformed teeth (peg-shaped laterals, talon cusps, megadont, microdont).
• Ectopic tooth position (palatal maxillary 3s).
• Early loss of primary teeth.
• Retained primary teeth.

Question 19

What is the difference between an anterior open bite formed due to the tongue or due to habits?

Answer 19

• Habits = asymmetrical (with posterior crossbites)

- Tongue = symmetrical.

Question 20

What do pathological cysts cause?

Answer 20

• Displacement of tooth germs
• Splaying of roots
• Failure of eruption
• Malocclusion