Tooth eruption/development

Question 1

How old cease growth of

i. Intercanine width

Answer 1

Mandibular – 8y/o; Maxillary: 13y/o

Question 2

How old cease growth of

ii. Arch width (2nd premolar to 2nd premolar)

Answer 2

13 y/o

Question 3

4 factors leading to median diastema

Answer 3

Hypertrophic labial frenum, peg-shaped lateral incisors (causing tipping of central incisor), excessive anterior openbite, mesiodens

Question 4

3 main causes of median diastema

Answer 4

• Supernumerary teeth/ high frenum attachment / missing or peg-shaped laterals
• Actually it is normal during the ugly duckling stage as eruption of canine cause tipping movement of central incisors, self-closure occur if space is small

Question 5

What consideration needed concerning retention after correction of median diastema?

Answer 5

• Relapse if space distal to central incisors has not been closed
• Re-migration of frenum attachment after frenectomy
• Bonded flexible wire can be attached to palatal sides of two central incisors to prevent space reopen

Question 6

Name the stage of treatment provided

Answer 6

• Retention stage (Ortho tx involve 3 stages: planning> active > retention)

Question 7

What do you need to pay attention to in retention stage?

Answer 7

Whether the teeth move back to before; any occlusal changes

Ken: Whether teeth have moved towards original position + any occlusal changes

Question 8

a. Define infraocclusion. (1)

Answer 8

Infraocclusion is a condition where teeth are found with their occlusal surface below the adjacent teeth, long after they should have reached occlusion.

Question 9

b. At what stage of root formation does eruption of permanent dentition occur? (1)

Answer 9

Two-third of final root length

Question 10

c. At what age will you extract a lower permanent first molar of poor diagnosis to provide maximum space closure and minimum tipping of lower permanent second molar? (1)

Answer 10

• When the roots of the second permanent molars are beginning to develop
• 8.5-9.5 y/o

Question 11

d. What radiographic features will you find on the 7 to satisfy the above circumstance? (1)

Answer 11

• Root development at least to bifurcation
• the angle between the long axis of the crypt of the lower second permanent molar and the first permanent molar is between 15° and 30°;
• the crypt of the second molar overlaps the root of the first molar (a space between the two reduces the likelihood of good space closure).

Question 12

When do the development of enamel of the 1st permanent molar and maxillary incisor start respectively? During which time frame wound an insult cause a defect? (3)

Answer 12

1st permanent molar: at birth
Maxillary central incisor: 3-4 months after birth
Maxillary lateral incisors: 10-12 months after birth
Time frame: birth to 5 years (until crown completed)

Question 13

A 8-year-old boy with a maxillary incisor unerupted,

i) list 3 possible complications (3

Answer 13

• Ectopic/displacement/rotation of the unerupted incisors
• Loss of space
• Midline shift
• UE incisor – enlarged follicle; cystic changes
• Adjacent teeth/nearby structures – ectopic/displacement/rotation; root resorption; opposing incisor overerupts;

Question 14

List 5 clinical features that you will suspect of an ectopic pathway of eruption of permanent upper canine. (5)

Answer 14

• Retention of deciduous canine
• Delayed eruption of permanent canine
• Congenitally missing lateral incisors / Peg-shaped or diminutive lateral incisors
• Rotation, tipping, drifting or displacement of adjacent teeth
• Presence of palatal bulge or absence or displacement of buccal bulge

Question 15

At what age can you palpate an upper permanent canine from the buccal sulcus? (1)

Answer 15

• 10 - 11 y.o.

Question 16

Apart from palpation, name a technique that you can locate a impacted canine. (1)

Answer 16

• Parallax technique, following SLOB rule

Question 17

What radiographic views will you want to locate the impacted canine? (2)

Answer 17

• Vertical: Anterial occlusal + periapical radiograph or panoramic
• Horizontal: 2 peripaical or 1 with panoramic

Question 18

At what age will you extract a deciduous upper canine to facilitate eruption of the succeeder? (1)

Answer 18

• 11 y.o ?

Question 19

What are the management guidelines if the canine do not erupt even after extraction of the deciduous upper canine? (4)

Answer 19

• Check the presence of obstacles (e.g. supernumerary) and remove if present
• Ensure there is sufficient space for canine eruption (i.e. space creation first)
• Surgical exposure either closed or open technique used
• Orthodontic traction
• Align with subsequent orthodontic treatment

Question 20

What are the four sequences apposition of enamel and dentin?

Answer 20

Mechanism of dentinogenesis:
1 – Differentiation of the odontoblasts – initiated by epithelial signals (Many small cell processes at first, but then these reduce in number later on)
2 – Peripheral ectomesenchymal cells divide
3 – pre-odontoblast cells differentiate
4 – synthetic organelles enlarge and proliferate
5 – nucleus moves basally + cells become polarised
6 – odontoblast retreats, since dentine matrix is laid down
7 – once the 1st layer of dentine is laid down, the differentiated ameloblast begin to deposit matrix

Anson (a lot of schematics and a table on page 95 if interested)