Descriptive Anatomy of the Permanent Mandibular incisors

Question 1

How are the mandibular permanent incisors different to the maxillary ones?

Answer 1

Mandibular permanent incisors are smaller and have smaller mesio-distal dimensions than any other teeth.

Question 2

Which permanent mandibular incisors are smaller?

Answer 2

The central incisor

Question 3

What are the general characteristics of permanent mandibular incisors?

Answer 3

The crown is wider labio-lingually than mesio-distally.

The crown inclines more lingually than in the upper incisors and the incisive edge can be seen to be on the lingual side of the central axis of the root.

Question 4

How is the incisal edge shaped in mandibular permanent incisors?

Answer 4

Both mesio-incisal and distoincisal edges are identical

Question 5

How is the root shaped in the permanent mandibular incisors?

Answer 5

Both mesial and distal root surfaces have grooves along their length. However, the distal root surface is more marked and clear.

The root tends to curve distally

Question 6

What significant difference does the mandibular central incisor have compared to the other teeth of the permanent dentition?

Answer 6

It is the smallest tooth in the permanent dentition

It is the second permanent tooth to erupt

Question 7

What are the mesiodistal and labiolingual dimensions of the crown and root in mandibular permanent incisors?

Answer 7

The crown and the root are narrow mesiodistally but are wider labiolingually.

Question 8

When is the initial calcification of mandibular permanent incisors?

Answer 8

It takes place 3 - 4 months after birth

Question 9

When is the crown completed in mandibular permanent incisors?

Answer 9

4 - 5 years of age

Question 10

When do the permanent mandibular incisors erupt?

Answer 10

Centrals: At 6 - 7 years of age.

Laterals: At 7 - 8 years of age.

Question 11

When is the root completed in mandibular permanent incisors?

Answer 11

At 9 years of age

Question 12

What are the features of the labial aspect of the mandibular permanent incisors?

Answer 12

They are smooth and tend to be convex particularly in the cervical third and flattens out toward the incisive third.

The crown is so symmetrical that it is difficult to tell left from right when evaluated in the mouth?

Question 13

How is the crown of the mandibular permanent incisor shaped?

Answer 13

The mesial and the distal outlines on the crown are fairly straight near the almost flat incisal edge; then the crown tapers from incisal edge towards the convex cervical line.

The roots are longer than the crowns significantly

Question 14

Where do the permanent mandibular incisors make contact with each other?

Answer 14

Just under the incisal edge

Question 15

How is the mandibular permanent incisor shaped?

Answer 15

Single root, usually straight

Narrow and convex mesiodistally

Mesial and distal outlines are straight down to apical portion

Apical third curves slightly distally and ends in a small pointed apex.

Root is longer than the crown.

Question 16

Which surface of the crown of the mandibular central incisor is narrower?

Answer 16

The crown is narrower on lingual surface than on labial surface

Question 17

How is the cingulum shaped in mandibular incisors?

Answer 17

Small, convex, and centered

Question 18

How is the lingual fossa shaped on the permanent mandibular incisors?

Answer 18

The lingual surface is smooth and shallow, just slightly concave in the middle and incisal third.

Question 19

How are the marginal ridges oriented in the lingual aspect of the mandibular incisor’s crown?

Answer 19

The marginal ridges and lingual fossa are scarcely discernible

Question 20

What shape does the crown of the mandibular incisors have when viewed mesially?

Answer 20

The geometric outline is triangular and it is referred to as being wedge shaped.

Labial outline is convex from cervical line to the incisal edge

Lingual outline is convex from cervical line to about 1/3rd the way up before there is a concave middle third followed by straight incisal third

Question 21

What shape does the cervical line of the mandibular incisor have when viewed mesially?

Answer 21

It has a deep curvature that extends incisally.

Question 22

How is the mesial aspect of the root of the mandibular incisor shaped?

Answer 22

The labial and lingual sides of the root are nearly straight from cervical line to the middle third then the root tapers towards the apex.

There is a broad and deep longitudinal depression for most of the root length

Question 23

How is the crown of the mandibular incisors shaped when viewed from the incisal side?

Answer 23

It is bilaterally symmetrical with little to differentiate the mesial half from the distal half.

The labial surface is slightly convex in incisal third towards labial side.

The cingulum is centered, smooth and makes a narrow convex outline.

Question 24

How does the labiolingual aspect of the mandibular incisor compare to the mesiodistal aspect?

Answer 24

The labiolingual measurement of the crown is slightly larger than the mesiodistal aspect.

Question 25

Which mandibular permanent incisor is wider mesiodistally?

Answer 25

The lateral permanent mandibular incisors

Question 26

How does the mandibular lateral incisor differ from the central incisor?

Answer 26

The crown is tilted distally on the root giving the impression that the tooth has been bent at the cervix. This makes the outline of the crown more shorter than the mesial.

Due to this curvature the mesial and distal contact areas are not on the same level.

Question 27

Where do the mandibular lateral incisors make contact with adjacent teeth?

Answer 27

Mesial: Incisal third near the mesionincisal angle.

Distal: In the incisal third but cervical to the level of the mesial contact area.

Question 28

How is the root of the lateral mandibular incisor different to that of the central mandibular incisor?

Answer 28

It appears very narrow mesiodistally and tapers very gradually from the cervical line. This makes it curve more distally.

Cingulum lies slightly distal to the axis line of the root.

Marginal ridges and the lingual fossa usually are not conspicuous.

Root is convex, smooth and narrower than the labial side.

Question 29

What are the general characteristics of the sidewards view of the mandibular incisors that differentiate them from the central incisors?

Answer 29

The distal surface is shorter incisocervically

The mesial cervical line has a deep curvature both cervical lines are less than those of the central incisor.

They also have the same longitudinal developmental depressions on the roots.

Question 30

What are the identifying features of the mandibular permanent central incisors?

Answer 30

Single root, flattened mesiodistally, tends to curve distally.

Incisive edge at right-angles to a line bisecting crown labiolingually.

Root is 12 mm long.

Distal longitudinal groove on root more marked than mesial.

Smallest tooth in permanent dentition.

Question 31

What are the identifying features of the mandibular permanent lateral incisor?

Answer 31

Slightly larger than lower central incisor; fan shaped crown, incisive edge wider mesiodistally.

Incisal aspect: Incisive edge not at right-angles to bisecting line of root but twisted to follow line of dental arch

Root is 14 mm long

Mesial surface of crown slightly longer than distal so that incisive edge slopes slightly

Fiant mesial and distal marginal ridges but more pronounced than in lower first incisor