PREMOLARS
There are eight of them, either four per arcade or two per semi-arcade.
They are located immediately behind the canines and in front of the molars.
Together with the molars, they form the group of posterior teeth or cusp group.
They carry at least two cusps.
They are the only ones to have only one vestibular cusp. The additional cusps are always lingual.
I- AVERAGE MEASUREMENTS;
Total height: 21mm.
Start of calcification : 3 to 4 years (approximately).
Eruption: 9 to 12 years (approximately).
Complete calcification: 11 to 14 years (approximately).
II-MORPHOLOGICAL CHARACTERS:
This tooth has the particularity of having two roots, it is the only one
premolars which is in this case.
a- Crown:
Irregularly cuboid.
a.1° Vestibular face.:
It presents, in a smaller and less accentuated form, the same characteristics as the vestibular face of the upper canine.
However, the V formed by the free edge is more open
Height: 8mm.
Mesio-distal diameter: 7mm.
It is narrower in the occluso-cervical direction than the crowns of the anterior teeth.
The occlusal contour resembles the incisal edge of the canine. The vestibular cusp tip is pronounced and divides the vestibular contour into two slopes:
The mesial slope is longer and straighter while the distal slope is shorter and curvilinear before any abrasion
The vestibular surface is marked by a significant vestibular ridge, two triangular depressions on either side of the median ridge divide the surface into 3 lobes.
The distal contact point (after abrasion) is more occlusal than the mesial contact point (located at the occlusal ¼ of the crown height).
a.2° Palatine face;
Smaller than the vestibular face,
Height: 6.5mm. Mesio-distal diameter: 6mm.
Its silhouette is similar to that of the vestibular face. Same semi-circular shape of the cervical edge, same asymmetry of the free edge, but its modeling is completely different.
Very convex in both directions, especially in the horizontal direction where it appears in the form of a semicircle.
In the vertical direction from the cervical quarter, it becomes very oblique from top to bottom in the vestibular direction. It is absolutely smooth, does not present any groove, and consequently, is not divided into lobes like the vestibular face.
a.3° Mesial face; On the incisors and canines, the proximal faces are narrower than the mesial faces
vestibular;
for the premolars, it is the opposite, these teeth being flattened in the mesio-distal direction.
Silhouette: It is wider than it is tall.
Height: 8mm, Vestibulo-buccal diameter: 9mm.
Cervical edge: no longer V-shaped as on the incisors and canines, it is simply a little concave.
Its general direction is not horizontal, it tilts slightly from top to bottom in the vestibulo-lingual direction.
Diameter: 7.6mm
Vestibular edge: As for the other teeth, convexity at the cervical third.
Lingual edge: A little less high than the previous one.
Its convexity is located in the cervical quarter, its other three quarters form a slightly convex line.
Directed obliquely from top to bottom, in the vestibular direction.
Free edge: Has the shape of a circumflex accent.
It is shorter than the cervical edge: only 5mm
Modeled: For the lower half, a very attenuated hump. For the upper or cervical half, a well-marked depression especially in the middle. The hump and depression blend together without a clear demarcation.
The bump corresponds to the mesial marginal crest of the grinding face and the depression represents the expansion of the interradicular groove.
a.4° Distal face:
Silhouette: similar to that of the mesial face, very slightly less high.
More vigorous modeling.
The lower hump, which responds to the distal marginal crest of the crown, is more accentuated.
a.5° Grinding face or occlusal face;
It is formed of two very prominent cusps.
one vestibular, one lingual.
Of the two cusps, the vestibular is the stronger.
Lingual edge: Smaller than the previous one: 6mm
Only, it forms a semicircle, without undulation.
The lingual surface being smooth.
Mesial and distal edges: Very slightly convex, almost straight, converging towards each other in the lingual direction.
Modeled: The transverse ridge (cutting edge) of the vestibular cusp forms a slightly wavy line with marked convexity in the center.
Overall, this line is less convex than the line representing the vestibular edge.
In the center, these two lines are separated by a space of 1mm. On the sides, they join and connect with the edges of the marginal ridges.
Same arrangement for the transverse edge of the lingual cusp, but the line representing this edge is semi-circular and the distance which, in the center, separates it from the line representing the buccal edge, is a little greater: 1.5mm.
The space between the two transverse edges, vestibular and lingual, represents the occlusal face itself or functional.
The diameter between the two tips of the cusps is 6mm.
Both cusps are very prominent.
The axial edge of the buccal cusp exactly extends the axial edge of the vestibular cusp, but the set of these two edges is slightly offset to the mesial side.
This means that the distal side of each cusp is slightly larger than the mesial side.
The two cusps are separated by a deep groove, but the vestibular cusp being a little stronger than the lingual cusp, the groove does not separate the occlusal face into two strictly equal parts;
it is placed a little closer to the lingual edge than to the vestibular edge
The groove is straight, it ends at each of its ends, mesial and distal, by a dimple.
So there is a mesial dimple, located near the mesial edge and a distal dimple located near the distal edge.
These edges, mesial and distal, are formed by two strong crests called marginal crests, which laterally join the vestibular cusp to the lingual cusp.
So there is a mesial marginal ridge and a distal marginal ridge.
b. Root:
Almost always bifid. It is then made up of two attached roots: one vestibular, one lingual. The vestibular is slightly stronger.
These two roots, separated by a variable length, are always joined at least on their lower third.
However, a very deep groove differentiates them, the interradicular groove. This groove even extends onto the crown where it flourishes.
Vestibular root:
*Height: l3mm.
*Mesio-distal diameter at the neck: 5.4mm.
Palatal root:
Height: l2.5mm.
Mesio-distal diameter at the neck: 4.7mm
When the tooth has only one root, this is always crossed on each proximal face by a well-marked groove which opens onto the crown.
c- Pulp chamber; Quite large, has two well-marked horns corresponding to the two cusps.
The vestibular horn is more developed than the lingual horn.
The pulp chamber continues with two canals finer than those of the incisors and especially the canines.
The two channels are roughly equal in size.
When the tooth has only one root, there may be two canals or a single canal that is very flattened in the mesio-distal direction.
III- SITUATION IN THE MOUTH;
. Vestibulo-lingual direction: The vestibular face of the crown is vertical. The tip of the vestibular cusp reaches the same level as the lingual cusp. The roots are inclined to the palatal side, a little less than for the upper canine: approximately 18 degrees with the vertical.
Mesio-distal direction: Crown barely inclined on the distal side; the root a little more: approximately 3 degrees with the vertical
PREMOLARS
Early cavities in children need to be treated promptly.
Dental veneers cover imperfections such as stains or cracks.
Misaligned teeth can cause difficulty chewing.
Dental implants provide a stable solution to replace missing teeth.
Antiseptic mouthwashes reduce bacteria that cause bad breath.
Decayed baby teeth can affect the health of permanent teeth.
A soft-bristled toothbrush preserves enamel and gums.