Lower premolars
The first lower premolar
• Start of calcification: end of the 3rd year
• Complete calcification: 11-14 years
• Eruption between: 9 – 11 years approximately
• HT=23 mm
• It is longer than the upper premolars
• Its bicuspid character is less pronounced
• Its general shape is similar to that of the lower canine.
A-The crown:
1/ The vestibular face:
– Similar to that of the lower canine but smaller.
– The free edge is less pointed.
– The bulge is located at the lower 1/3 coronary.
2/ The lingual face:
– It is much smaller than face V, it barely exceeds ½ the height of face V.
– It is convex in the vertical and horizontal directions.
3/ The proximal faces:
– Unlike the PM sup, they are taller than they are wide (7.5mm, 8mm).
– They converge towards each other at the collar.
4/ The occlusal face:
– Seen from the front, it is almost circular,
– Has 2 cusps, one vestibular and one lingual,
– The V has double the width and height of the lingual
– Very marked obliquity 45°.
– An intercuspal groove MD, placed near the lingual edge, barely marked and very shallow, separates the 2 cusps.
– There are 2 marginal pits, 1 mesial and 1 distal
– There are 2 marginal ridges, 1 mesial and 1 distal.
B-The root:
– It is unique, conical, flattened in the MD direction.
– Has the same characteristics as the root of the canine < .
– It is smaller and more slender.
– No groove on the proximal faces
C-The pulp chamber:
It has two pulp horns: a very large vestibular one and a very small lingual one.
D-Situation in the mouth:
VL meaning:
– The V face of the crown is slightly more inclined on the L side than on the lower canine,
– The occlusal face is oblique from top to bottom in the lingual direction,
– The root has an oblique inclination of 2.5°/vertical from bottom to top in the lingual direction.
MD Meaning:
– The entire tooth has a vertical direction
– Slightly more inclined than that of the lower canine.
The second lower premolar
• Start of calcification: around 4 years;
• Complete calcification: approximately 12 ½ years;
• HT = 23.5 mm;
• Eruption: approximately 11 to 13 years.
• Its crown has a cubic shape which brings it closer to that of the molars,
• Most often, it has 3 cusps (sometimes only 2).
A- The crown:
1/ Face V:
– It is larger than on the 1st lower PM,
– The free edge is not pointed,
– The central lobe barely exceeds the side lobes,
– The overall modeling is comparable to that of the 1st PM inf.
2/ The L side:
– A little less high than the V face, barely less wide.
– Its free edge can appear in 2 ways depending on whether the crown has 2 or 3 cusps.
In the case of 2 cusps:
Free edge has a single, very blunt point.
In the 3-cusp case:
– The free edge is divided into 2 points (the mesial point being slightly wider than the distal point) by a small groove which comes from the occlusal face and which immediately merges into the L face.
– This face is slightly convex in the vertical and horizontal direction as for the 1st lower PM, it is a little oblique from bottom to top in the L direction.
3/The proximal faces:
They are a little wider than they are tall.
4/The occlusal face:
2-cusp case:
– Cusp V is the most prominent and strongest;
– The MD groove is curved with concavity V;
– The marginal dimples are therefore found closer to the V edge than to the L edge.
3-cusp case:
– The L cusp is divided into 2 small cusps by a groove in the VL direction which starts from the MD groove and ends on the L face.
– The set of 2 furrows gives the shape of a Y;
– There are 2 marginal dimples 1M and 1D;
– There are 2 marginal ridges 1M and 1D.
B-The root:
It has the same conformation as the 1st lower premolar, however it is stronger, generally no groove on the proximal faces.
C-The pulp chamber:
■ It has 2 or 3 horns, depending on whether the crown has 2 or 3 cusps
■ The root canal is very slightly flattened in the MD direction.
D-Situation in the mouth:
Same general inclination as the 1st lower premolar, only the occlusal face is much less oblique.
Differential characteristics of premolars:
A/ Between the upper PM and the lower PM:
B/ Between the 1st PM sup and the 2nd PM sup:
| 1st PM sup | 2nd PM sup |
| the 1st PM sup is slightly larger than the second | |
| A cusp L with a diameter VL smaller than that of its cusp V | Two cusps of equal diameter |
| The 2 cusps do not reach the same level, cusp V is more prominent. | Two cusps of equal value projecting |
C/ Between the 1st lower PM and the 2nd lower PM:
| 1st PM inf | 2nd PM inf |
| the 1st is clearly less bulky than the second. | |
| a circular shape | a cubic shape. |
| the L cusp is very small, which gives the occlusal face a very marked obliquity from top to bottom in the L direction. | the more developed cusp L which reaches almost the height of cusp V consequently the occlusal face is much less oblique than the 1st . Often this portion L is divided into 2 small cusps. |
Lower premolars
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