Primary Tooth Morphology

Question 1

What is the rule for order of eruption and what is the order of eruption

Answer 1

The lower teeth erupt before uppers with the exception of the lateral incisors
A,B,D,C,E
1,2,4,3,5

Question 2

What is the first tooth to erupt and when does this occur

Answer 2

Lower central incisor at 4-6 months

Question 3

When do each of the teeth in the primary dentition erupt

Answer 3

Central incisor - 4-6 months
Lateral incisor - 7-16 months
1st molar - 13-19 months
Canine - 16-22 months
2nd molar - 15-33 months

Question 4

When is the primary dentition completed

Answer 4

By 2 and a half to 3 years of age

Question 5

Contra lateral teeth usually erupt within what time period of each other

Answer 5

3 months

Question 6

What is the difference between primary and permanent incisors

Answer 6

The primary incisors are smaller in both crown and root proportions

Question 7

What is the difference between primary molars and permanent premolars

Answer 7

The primary molars are wider mesiodistally than the permanent premolars which take their place
Primary molar crowns are more bulbous

Question 8

Describe the first primary molar

Answer 8

Doesn’t look like any other teeth

Has a prominent mesiobuccal tubercle

Question 9

Describe the second primary molar

Answer 9

Have a transverse ridge running across the tooth - don’t want to cut through when doing preparations for the tooth
Looks like first permanent molar and has 3 buccal cusps

Question 10

Compare the roots of primary teeth and permanent teeth

Answer 10

Roots of primary teeth tend to be narrower
Roots of primary molars are longer and more slender than the permanent molars
Primary molar roots tend to flare apical to allow room in between for the permanent tooth crowns

Question 11

Compare the pulp of primary and permanent teeth

Answer 11

Pulp chambers of the primary teeth are relatively large in proportion to the crowns that surround them
Pulp horns of primary teeth extend high occlusally, placing them closer to the enamel than in permanent teeth - hence pulpal exposure on cavity preparation is more likely

Question 12

Why do primary teeth become non-vital quickly if infected with caries

Answer 12

There’s not much distance for the bacteria to go before they invade the pulp

Question 13

Compare the root canals of primary and permanent teeth

Answer 13

Primary tend to be ribbon shaped with multiple interconnecting and accessory canals and are clinically impossible to clean

Question 14

Compare the enamel and dentine between primary and permanent teeth

Answer 14

The enamel of the primary teeth is relatively thin and has a consistent depth
The thickness of the coronal dentine is much thinner than in permanent teeth

Question 15

Why is there spacing in the primary dentition

Answer 15

To prevent crowding in the permanent dentition

Question 16

Where is the anthropoid or primary spacing found

Answer 16

Mesial to upper deciduous canine

Distal to lower deciduous canine

Question 17

Define the leeway space

Answer 17

Extra mesio-distal space occupied by the primary molars which are wider than the premolars which will replace them

Question 18

What is the leeway space

Answer 18

Usually 1.5mm per side on the upper arch and 2.5mm per side in the lower arch

Question 19

How does the face grow as you grow

Answer 19

Downwards and forwards

Question 20

When does the mixed dentition start and end

Answer 20

Begins from the time the first permanent tooth erupts until the exfoliation of the last primary tooth
Usually between 6 and 11 years

Question 21

What is the eruption sequence of permanent teeth in the upper arch

Answer 21

First permanent molars and then front to back except canines

6,1,2,4,5,3,7,8

Question 22

What is the eruption sequence of permanent teeth in the lower arch

Answer 22

First permanent molars and then front to back

6,1,2,3,4,5,7,8

Question 23

What is the general rule for permanent teeth eruption

Answer 23

Lower teeth tend to erupt before upper teeth with the exception of second premolars

Question 24

Draw the eruption date table for permanent teeth

Answer 24

7,8,11,10,10,6,12
1,2,3,4,5,6,7
1,2,3,4,5,6,7
6,7,9,10,10,6,12

Question 25

Describe the ugly duckling phase

Answer 25

Transient spacing of the upper 1s due to the proximity of their roots the the erupting 2s and 3s
Central’s coming through and lateral is pressing on the root, flaring it out
As lateral comes down there is a canine pressing on the root there, flaring it out

Question 26

How long does completion of root formation take

Answer 26

From the date of eruption it takes around 3 years for the permanent tooth root to complete apexogenesis and 1.5 years on average in the primary dentition

Question 27

Describe the difference in size between the primary and permanent dentition

Answer 27

Primary dentition has a much shorter arch length