Postnatal Development of the Human Dentition

Question 1

During the 9-11 years of development (from 3-12/14 yrs of age), what should the dentist look out for need for intervention?

Answer 1

1. Recognising developmental anomalies
2. Recognising disruptions to the normal development of the dentition

Question 2

What are the basic knowledge principles in post-natal dental development?

Answer 2

1. Sequence and Timing of eruption
2. Leeway space
3. Root development and emergence of teeth

PLUS Observations of developing dental conditions

Question 3

What observations should warrant investigations and/or treatment?

Answer 3

1. Delayed (>6 months past normal range of eruption) and disturbance of eruption of permanent teeth (unilateral)
2. Difference in occlusal plane between posterior and anterior teeth –> possible thumb sucking?
3. Marked displacement of teeth (unilateral) eg. misalignment
4. Prolonged retention of primary teeth (unilateral or bilateral)
5. Premature loss of primary teeth (unilateral or bilateral)

Question 4

What is the normal eruption sequence of Primary teeth?

Answer 4

A, B, D, C, E

Question 5

At which stages is there an increase in arch length (depth) + width in a child’s jaw

Answer 5

Birth
6-8 months
9-10 months

24-30 months
30-72 months

Question 6

At which stages is the arch length (depth) and width of a child stabilized?

Answer 6

10-14months
14-18 months
18-24 months

Question 7

What is the eruption timing and sequence of children

Answer 7

Birth: NIL
6-8 months: 1/2 As (lower)
8-10 months: As
10-14 months: Bs
14-18 months: Ds
18-24 months: Cs
24-30 months: Es
30-72 months: NIL

Question 8

What is the clinical advantage of having spaced deciduous dentition over the closed dentition?

Answer 8

Spaced dentition results in better outcome in permanent dentition eruption as it allows larger permanent dentition to erupt without problems.

Question 9

What is the percentage of children with spaced deciduous dentition and closed deciduous dentition.

Answer 9

Spaced: 75%
Closed: 25%

Question 10

What is the normal first three permanent teeth to erupt?

Answer 10

6, 1, 2

Question 11

What is the eruption timing and sequence of the first 3 permanent dentitions?

Answer 11

5-6 yrs: 6s
6.2yrs: lower 1s start
7yrs: lower 1s completed, upper 1s start
7.3 yrs: lower 2s begins
8 yrs: upper 1s and lower 2s completed, upper 2s begins
8.5 yrs: upper 2s completed

Question 12

What does an ectopic mesial eruption of #16 cause?

Tx?

Answer 12

External root resorption of E distal

Most self correcting (66%)
If severe then extract and preserve space.

Question 13

What are the observations in the ectopic eruption of a molar?

Answer 13

Unilateral delayed eruption and difference in occlusal plane (E becomes overerupted)

Question 14

What factors to consider to resolve impaction of teeth

Answer 14

1. Root formation completion: incomplete = good potential for tooth eruption
2. Curvature of root: Substantial root curvature makes proper tooth positioning impossible as it can hit cortical bone easily if it is tracked

Question 15

What is the value of a CBCT

Answer 15

1. Visualize the true extent of displacement
   2.Stage of root formation and development of dilaceration
2. Ability to plan with oral surgeon best approach and position of attachment to be bonded to the crown
3. Increased understanding from parents after visualization and explanation on severity of displacement

Question 16

What is seen on the fingers in digit sucking habit patients

Answer 16

Callous formations

Question 17

What is the period between early and late mixed dentition stage and what changes happen then

Answer 17

8.5 - 9.8 years old

Nothing!

Question 18

What is the eruption sequence of permanent teeth (late mixed dentition)

Answer 18

U = 4, 5, 3, 7
L = 3, 4, 5, 7

Question 19

What is the eruption timing and sequence of the last 4 permanent dentitions?

Answer 19

9.8 yrs: lower 3s begin
10-10.5 yrs: lower 3s completed, 4s begin
11-11.5 yrs: 4s completed, 5s begin
11.5-12 yrs: 5s completed, upper 3 begins
12 yrs: upper 3 completed

Question 20

What is Leeway space

Answer 20

Leeway space (mm) = CDE - sum of 345

Question 21

What are the two principles of root development and emergence of tooth?

Answer 21

1. There is no vertical eruptive movement of dental crypt within the alveolar bone until half of root is formed
2. Crown emerges through the alveolar bone with 3/4 root formation

Question 22

What is the average time needed for root development from 25-50% (no movement of crypt) for 3, 4, 5

Answer 22

Canine: 2.25 yrs
First premolar: 1.5 years
Second premolar 1.5 yrs

Question 23

What is the average time needed for root development from 50-75% (eruption of crown) for 3, 4, 5

Answer 23

1.5 years

Question 24

Why is the average time needed for root development information important?

Answer 24

To determine when and for how long to place in a space maintainer.

Question 25

What is the consequence of early loss of primary 2nd molar and with no space maintained?

Answer 25

mesialisation of 6 –> inadequate space for eruption of 5

Question 26

How long should a space maintainer be placed if the root formation of the 4 is at 1/4 or <1/4 and the E is extracted?

Answer 26

1.5 yrs + 1.5 yrs = 3 yrs