Primary Tooth Morphology

Question 1

What role does the dental follicle play in tooth eruption?

Answer 1

The follicle is activated to initiate osteoclastic activity in the alveolar bone ahead of the tooth and this clears a path for tooth eruption.

Question 2

What is the rough approximation of calcifications of crowns at birth for all teeth?

Answer 2

½ of central incisors

¹/3 of lateral incisors

Tip of primary canines

½ of first primary molars

¹/3 of second primary molars

Tip of cusps of first permanent molars.

Question 3

What is the order of eruption of primary teeth?

Answer 3

ABDCE, lower teeth tend to erupt before uppers EXCEPT the lateral incisors.

Usually the first primary tooth to erupt is the lower central incisor at 4-6 months (In FDI notation teeth 81 and 71).
Next is the lateral incisor (7-16 months) 
    52,62,72, and 82
1st molar (13-19 months)
    54,64,74, and 84
Canine (16-22 months)
    53,63,73, and 83
2nd molar (15-33 months)
    55,65,75 and 85

Question 4

How many months should the primary dentitions contralateral tooth erupt within?

Answer 4

3 months.

Question 5

What are the differences between primary and permanent teeth crowns?

*note: Enamel is also thinner in permanent teeth and there is less dentine. Caries progression is therefore faster in primary teeth.

Answer 5

1. The primary incisors are smaller in both their crown and root formations.
2. The primary molars are wider mesio-distally than the permanent premolars which take their place.
3. Primary molars are more bulbous.
4. The primary teeth are usually whiter in colour as the enamel structure is slightly different.

Question 6

What is a main characteristic of an upper 1st primary molar?

Answer 6

Prominent mesio-buccal tubercle.

Question 7

What is a main characteristic of an upper 2nd primary molar?

Answer 7

They have a traverse ridge.

Question 8

What is a main characteristic of a lower 2nd primary molar?

Answer 8

They have 3 buccal cusps like a first lower permanent molar.

Question 9

What are the differences between primary and permanent teeth roots?

Answer 9

1. The roots of primary teeth tend to be narrower when compared to their permanent counterparts.
2. The roots of primary molars are longer and more slender than the roots of the permanent molars. These roots tend to flare apically to allow room in between for the developing permanent tooth crowns.

Question 10

What are the differences between primary and permanent teeth pulps?

*note: primary teeth have larger pulps and therefore need to have smaller instruments used on them.

Answer 10

The pulp horns of primary teeth extend higher occlusal placing them closer to the enamel than permanent teeth. Pulpal exposure is on cavity prep is more likely.

Question 11

What are the differences between primary and permanent teeth root canals?

Answer 11

Primary teeth tend to have more ribbon shaped (flat and thin) with multiple interconnecting and accessory canals.

Question 12

What are the differences between primary and permanent teeth hard tissues?

Answer 12

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

Question 13

What are the differences between primary and permanent teeth occlusion?

Answer 13

There is more anterior spacing in primary teeth to allow room for the permanent dentition.

Question 14

What is the leeway space?

Answer 14

Leeway Space- extra mesio-distal space occupied by the primary molars which are wider than the premolars which will replace them
Usually equates to 1.5mm per side on the upper arch and 2.5mm per side in the lower arch.

Question 15

When does the mixed dentition start?

Answer 15

The mixed dentition stage begins from the time the first permanent tooth erupts, until the exfoliation of the last primary tooth.
This is usually the time between 6 (1st perm molar) and 11 years of age (upper primary canine) but there are variations of normal.

Question 16

What is the eruption sequence of permanent teeth?

Answer 16

Upper arch :

1st permanent molars & then front to back EXCEPT canines.
i.e 6, 1, 2, 4, 5, 3, 7, 8.

Lower arch :

1st permanent molars & then front to back.
i.e 6, 1, 2, 3, 4, 5, 7, 8.

Question 17

What tooth does crowding in the upper and lower arch lead to?

Answer 17

Aid memoire: crowding in the upper arch usually leads to the exclusion of the upper canine, crowding in the lower arch usually leads to lack of space for the second premolar.