Development of the dentition

Question 1

List the ideal features of the primary dentition

Answer 1

• Spacing of incisors
• Anthropoid spaces
• Midline diastema
• Upper and lower Es are in the same terminal plane
• Lower incisors occlude on cingulum of upper incisors

Question 2

What is the ideal incisor relationship in the primary dentition?

Answer 2

• Deep overbite at first which then reduces over 3-4 years

- At 5 there is edge to edge occlusion which may cause marked dentition

Question 3

Why is the primary incisor occlusion initially a deep overbite?

Answer 3

At birth, the lower gum pad is slightly distal to the upper gum pad

Question 4

What can change the incisor relationship in the primary dentition?

Answer 4

• Digit sucking resulting in an asymmetrical increased overbite and overjet

Question 5

What is the ideal amount of spacing of incisors in the primary dentition?

Answer 5

> 6mm spacing of primary incisors to allow permanent incisors to align (Leighton)

Question 6

What happens if there is crowding in the primary dentition?

Answer 6

The permanent dentition will be severely crowded

Question 7

What is the ideal E relationship in the primary dentition? Why?

Answer 7

Flush terminal plane - as it will result in a class I occlusion in the permanent dentition

Question 8

What happens if there is a mesial step in the primary E relationship?
Is this common?

Answer 8

- Can lead to class III or class I 
(HOWEVER THIS IS RARE AS THE MANDIBLE IS LAGGING BEHIND MAXILLA)

Question 9

What happens if there is a distal step in the primary E relationship?

Answer 9

Class II molar relationship

Question 10

Where are the anthropoid spaces located?

Answer 10

Mesial to the upper C

Distal to the lower C

Question 11

List some things that can go wrong in the primary dentition

Answer 11

• Incisor protrusion from digit sucking habit
• Posterior crossbite due to sucking habits
• Abnormalities in tooth number - supernumeraries or premature loss of primary tooth
• Tooth to tissue ratio causing predilection for crowding
• Anteroposterior discrepancy

Question 12

What are the 3 stages of the permanent dentition development?

Answer 12

Stage 1 (age 6-8) - eruption of the 6s and incisors

Stage 2 (age 11-12) - eruption of canines, premolars and 7s

Stage 3 (18-25) - eruption of 8s

Question 13

Where does extra space come from when the permanent incisors erupt?

Answer 13

• Spacing in the primary dentition
• Permanent incisors are proclined (gives 1-2mm extra space)
• Increase in intercanine width
• Leeway space

Question 14

How much space is provided from the increase in intercanine width in the maxilla and mandible

Answer 14

Maxilla - 3mm

Mandible - 2.5mm

Question 15

Where is extra space provided in the mandible for the permanent teeth?

Answer 15

• Transitory lower incisor crowding from ages 8-9

- Distal shift of lower 3 when the D is exfoliated giving 1mm of space

Question 16

What issues can occur at stage I in permanent dentition development?

Answer 16

• Premature loss of E causing drift of the 6 causing impaction of the 5s
• Missing central (impaction)
• Missing laterals - hypodontia
• Abnormal form (peg lats, microdontia)
• Loss of permanent teeth from trauma
• Crossbites

Question 17

If an E is retained but the 5 is present radiographically, what should be done?

Answer 17

Leave it, the 6 is present therefore the E will exfoliate with eruption of the 6
If >6 months - then extract the E

Question 18

What is the management of a patient in the mixed dentition who is digit sucking?

Answer 18

Needs to be stopped asap as there is still chance for spontaneous improvement in this stage

Question 19

How does leeway space arise?

Answer 19

The combined width of the primary canines, first molar and second molar (CDE) is more than the width of the permanent successors

Question 20

What is leeway space?

Answer 20

Surplus of space provided for the permanent teeth to erupt in alignment

Question 21

What is the width difference between lower E and lower 5s

Answer 21

Lower E is 2mm larger than lower 5

Question 22

What is the space difference between lower D and lower 4

Answer 22

Lower D is 0.5mm larger than lower 4

Question 23

What is the space difference between upper E and upper 5

Answer 23

Upper E is 1.5mm larger than upper 5

Question 24

What is the space difference between upper D and upper 4

Answer 24

Upper D slightly larger than upper 4

Question 25

When does the stepped class I relationship occur?

Answer 25

When all the deciduous teeth have been replaced and the upper 6 moves mesially to a lesser extent of the lower 6

Question 26

Issues at stage 2 of the permanent dentition development

Answer 26

• Delayed eruption of 3s - need to check palpation
• 4s erupt before 3s
• 5s impacted or lingually displaced
• Hypodontia and ankylosis
• Asymmetries of eruption

Question 27

When should canines be palpated in the buccal sulcus?

Answer 27

From age 9 annually

Question 28

What happens if you cannot palpate the canines bucally?

Answer 28

• Take radiograph with parallax technique
• If palatally placed (shown on radiograph or palpated buccally then refer)
• Monitor if patient still young

Question 29

What happens if you palpate the canines palatally?

Answer 29

Refer to orthodontist asap

Question 30

What issues can occur at stage 3 of the permanent dentition development?

Answer 30

• Impaction of 8s (common)

- Late lower incisor crowding