The first lower premolar

The first lower premolar

1. Timeline: 

• Start of calcification: 21 to 24 months.
• End of coronary calcification: 5 to 6 years.
• Eruption: 9 to 12 years.
• End of apical calcification: 12 to 13 years .

2. Average measurements:

Total height: 22.5 mm.

Crown height: 8.5mm.

Coronal mesio-distal diameter: 7 mm.

Coronal vestibulo-lingual diameter: 7.5 mm 

3. Description 

1. Vestibular face: 
2. The crown:

• The general outline is that of a pentagon like

 for the canine. 

• The occlusal contour is dominated by a point 

marked cusp. This point divides the outline 

occlusal in 2 slopes: one mesial and the other distal.

• The mesial slope is generally short and 

straight while the distal slope is long and 

concave. These slopes join the contours 

proximal with rounded angles.

• The crown is asymmetrical.                                                                           
• The entire vestibular surface is 

convex, both in the occluso-cervical direction 

than in the mesiodistal direction.

• The median lobe is the most prominent, there are 

triangular depressions on either side of 

this median lobe.

2. The root:

• It is conical and generally rectilinear.
• Its proximal contours converge towards a 

pointed apex.

• The vestibular surface is convex.

2. Lingual face: 
3. The crown  :

• The entire lingual surface is smaller than the face

  vestibular.

• More than half of the occlusal area is visible at

observation by this face: this is due to the strong

 lingual inclination of the occlusal surface. 

• The lingual cusp tip is a minor elevation,

 However, it is strongly conical and pointed, it can 

occupy a middle position as it can be 

offset to the mesial or distal side.

• The lingual surface is uniformly convex and free 

of any lobe or depression. 

2. The root:

• The root lingual surface is narrower 

that the root vestibular face due to 

of lingual convergence of the proximal walls 

root

• It presents as a whole a surface 

Convex.

3. Mesial face: 
4. The crown:

• The general outline is trapezoidal; this is linked to a 

very short lingual contour.

• The vestibular contour is strongly prominent

and the maximum convexity is located in the 1/3 

cervical, from this 1/3, the vestibular contour

  tilts sharply in a lingual direction to the 

  cusp tip. 

• The lingual contour is convex and the maximum 

convexity is located in the occlusal third. 

• The lingual cusp tip is most often located

 in line with the root lingual contour: this is a

 rule for mandibular premolars. 

• It is the only dental unit in the posterior group for

which the occlusal surface is inclined relative to

    the coronoradicular axis of the tooth.

• The cervical line is barely convex towards

 the occlusal area 

• The mesial surface is convex in the direction 

occlusocervical in the occlusal 1/3. It is rather 

concave in the medial 1/3 and in the cervical 1/3

• The maximum convexity of the mesial wall is located

at the junction of the vestibular 1/3 and the medial 1/3

in the vestibulo-lingual direction and at the junction of 1/3 

occlusalet of the median 1/3 in the occluso-cervical direction

2. The root:

• It is wider in the vestibulolingual direction than 

in the mesiodistal direction

• It ends with a pointed apex
• The root surface as a whole is barely 

convex or flat

• Sometimes there is a longitudinal depression 

deep.

4. Distal face: 

a. the crown:

• Observation of this tooth from the distal face is 

basically similar to the mesial view.

• The distal marginal ridge is more prominent than 

  the mesial marginal ridge. 

• The proximal contact zone is larger. 

b.the root:

• In general, the root is convex in the 

    vestibulolingual sense

5. Occlusal face: 

• The general outline resembles that of a 

”  cut diamond  ” 

• The vestibular contour is “V” shaped

 with a convex tip, the summit of this V, corresponds to 

the vestibular ridge, and is located directly above the tip

 cusp.                             

• Proximal contours converge toward the face 

lingual, the mesial contour is slightly convex 

sometimes straight it is interrupted by the furrow 

mesiolingual the distal contour is considerably

 more convex than the mesial contour

• The lingual contour is convex. It is formed by a small circular arc whose diameter is approximately half the diameter of the circular arc that forms the vestibular surface.
• The occlusal area is triangular: the base of the triangle 

     corresponds to the mesial and distal slope of the cusp 

    vestibular, and the summit corresponds to the tip of the

   lingual cusp. 

• The occlusal area is made up of 2 cusps of 

different size:

* The wide vestibular cusp occupies the most 

large mesiodistal diameter, the tip 

cusp is located approximately on the line 

median vestibulolingual.

* The lingual cusp is a small elevation

 whose volume does not exceed half of 

that of the vestibular cusp.

• The mesial marginal crest is distinctly shorter, 

more straight, more inclined towards the region 

cervical, and less prominent than the marginal crest

distal.

• The central slopes of these cusps often form

 a continuous transverse edge from the tip 

vestibular cusp to cusp tip

lingual, this ridge separates the occlusal area into one half 

mesial and one distal half.

• The central groove , when it exists, is very far from the 

On the lingual side, the transverse ridge often interrupts this 

furrow. On either side are dimples .

The first lower premolar

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The first lower premolar