Descriptive anatomy of the mandibular permanent premolars

Question 1

How many premolars does the mandibular arch have?

Answer 1

4; 2 right and 2 left premolars.

Question 2

How many lobes are the mandibular permanent premolars derived from?

Answer 2

1st = 4 lobes as were the maxillary premolars.

2nd = in most instances 5; 3 buccal and 2 lingual.

Question 3

When does initial calcification occur in first mandibular permanent premolars?

Answer 3

in the first 1.75 - 2 years

Question 4

When does crown get completed in mandibular permanent premolars?

Answer 4

5 - 6 years

Question 5

When do the first permanent mandibular premolars erupt?

Answer 5

10 - 12 years

Question 6

When is the root of the first permanent mandibular premolar completed?

Answer 6

12 - 13 years

Question 7

What is the crown of the mandibular permanent premolars shaped like?

Answer 7

The geometrical outline of the crown is described as trapezoidal with the shortest of the uneven sides is
cervically.

Mesial and distal outlines are slightly concave from the cervix to the contact areas.

There is a continuous ridge from the cervical margin to the cusp tip which is called the buccal ridge (it is not as prominent as that on the maxillary first premolar)

Question 8

How many cusps does the first permanent mandibular premolar have?

Answer 8

2 cusps; a long and well-formed buccal cusp and a small non-functional lingual cusp. (lingual cusp is not longer than the cingulum found on the maxillary canine)

Question 9

Where is the tip of the buccal cusp of the first mandibular premolar located relative to the center of the crown?

Answer 9

The tip of the buccal cusp is, in most cases, located a little mesial to the centre of the crown buccally, similar to the mandibular canine.

Question 10

How is the convexity of the buccal cusp of the mandibular permanent premolar different to the maxillary premolars?

Answer 10

The buccal surface of the crown of the 1st mandibular premolar is markedly convex compared to the maxillary premolars especially at the cervical and middle thirds.

Cervically the crown is narrower mesio-distally than at the contact areas.

Question 11

Where are the mesial and distal contact areas of the mandibular permanent premolars?

Answer 11

The mesial and distal contact areas are nearly at the same level in the middle third, just occlusal to the middle of the crown.

The curvature of the distal contact area is broader than that of the mesial one.

Question 12

How is the buccal cusp of the first mandibular permanent premolar different to the mandibular second permanent premolar?

Answer 12

The buccal cusp is longer and more pointed than the buccal cusp on mandibular second premolars.

Question 13

Which cusp ridge is shorter the mesial or distal cusp ridge of the mandibular first permanent premolars?

Answer 13

Mesial cusp ridge is shorter than the distal cusp ridges.

Question 14

What can sometimes be seen in the occlusal third of the buccal surface on either side of the buccal ridge?

Answer 14

Vertical developmental depressions

Question 15

What is present on cusp ridges of permanent 1st mandibular premolars that allow the tooth to accomodate the opposing dentition?

Answer 15

Either cusp ridges usually show shallow notches (concavities) these are to accomodate the opposing dentition and are contoured to allow spillways during mastication.

Question 16

How is the lingual cusp different to the buccal cusp of the 1st permanent premolar?

Answer 16

The crown tapers lingually, so the lingual side is narrower than the buccal side.

The lingual cusp is always small, short, reaching about two-thirds the length of the crown and often has a
pointed tip.

Much of the occlusal surface of this tooth can be seen from the lingual aspect because of the shortness of
the lingual cusp

Question 17

What structure is the tip of the lingual cusp of the permanent first premolar related to?

Answer 17

The tip of the lingual cusp is in alignment with the triangular ridge of the buccal cusp.

The mesial and distal fossae are on each side of the triangular ridge.

Question 18

What structure separates the mesial marginal ridge from the mesial slope of the small lingual cusp?

Answer 18

There is a mesio-lingual developmental groove separating the mesial marginal ridge from the mesial slope of the small lingual cusp

Question 19

How many roots do mandibular first premolars have?

Answer 19

1 single root that is shorter than that of the lower canine.

Question 20

How is the mandibular first premolar shaped?

Answer 20

Apical third is bent distally and sometimes mesially.

Surface of the root distally shows more convexity than mesially.

Root is much narrower on the lingual surface than on the buccal surface.

Question 21

How are the 1st permanent mandibular premolar roots shaped?

Answer 21

The buccal and lingual sides of the root are nearly straight in the cervical half.

The root outline tapers apically to a blunt apex. Root apex is in line with the tip of the buccal cusp.

Occasionally apical third of the root may be divided into a buccal and lingual portion by a deep developmental groove ending in the bifurcation

Question 22

What kind of shape does the 1st mandibular permanent premolar have?

Answer 22

Rhomboidal.

Crown tilts lingually much more than any other premolar. This is why the tip of the buccal cusp is located centrally right over the root.

Question 23

What is the lingual cusp of the first mandibular premolar aligned with?

Answer 23

The lingual border of the cervical portion of the root.

Question 24

How do the cusp tips of the mandibular first permanent premolars differ from those of the maxillary side?

Answer 24

Both buccal and lingual cusp tips are well within the confines of the root trunks.

Question 25

How is the buccal outline of the mandibular first permanent premolar shaped?

Answer 25

It is prominently curved, the crest of the curvature is usually just occlusal to the cervical line, near the middle third of the crown.

Question 26

How is the lingual outline of the mandibular first permanent premolar shaped?

Answer 26

Curved outline of less convexity than the buccal surface.

Question 27

Where is the crest of curvature of the mandibular first permanent premolar?

Answer 27

About in the center of the crown length not far from the tip of the lingual cusp.

Question 28

Why does the lingual surface of the crown of the first mandibular premolar protrude past the root?

Answer 28

Due to the extreme tilting of the crown making a lingual overhang above the root lingually.

Question 29

How are the triangular ridges of the buccal and lingual cusp different?

Answer 29

Triangular ridge of the buccal cusp inclines sharply from the cusp tip towards the center of the occlusal surface while triangular ridge of the lingual cusp is short and in a nearly horizontal plane.

Question 30

How is the angle of the mesial marginal ridge of the first mandibular premolar related to the triangular ridge?

Answer 30

It is inclined dramatically parallel to the traingular ridge.

Question 31

How is the distal marginal ridge different to the mesial marginal ridge on the first mandibular premolar?

Answer 31

The distal marginal ridge is broader, flatter and longer than that of the mesial marginal ridge.

Question 32

What shape does the distal aspect of the mandibular permanent premolar have?

Answer 32

It resembles the mesial aspect (rhomboid shape) but it has a higher and more occlusal distal marginal ridge. (Which is unique to this tooth)

Question 33

What shape does the occlusal surface of the first permanent premolar have?

Answer 33

Occlusal shape varies depending on the number of lobes that are present. They can be diamond or round in shape.

Buccal cusp is very much larger than the lingual cusp and dominates the occlusal surface.

Question 34

What ridges and fossae does the occlusal surface of the mandibular first premolar have?

Answer 34

Long buccal triangular ridge and a short lingual triangular ridge. 2 triangular ridges unite and form a transverse ridge. On each side of which there is a fossa mesial and distal occlusal fossae.

Sometimes the transverse ridge is crossed near the center of the occlusal surface by a shallow central groove.

Question 35

What groove can cross the transverse ridge?

Answer 35

Sometimes the transverse ridge is crossed near the center of the occlusal surface by a shallow central groove.