文档介绍：MANDIBULAR FIRST PREMOLAR
Prof. A. El- Sahn
Initial Calcification
1¾ – 2 years
Completion of Crown
5 – 6 years
Eruption
10 – 12 years
Completion of Root
12 – 13 years
CHRONOLOGY
Prof. A. El- Sahn
al Aspect
The geometrical outline of the crown is roughly trapezoidal with the shortest of the uneven sides is cervically.
The mesial and distal outlines are slightly concave from the cervix to the contact areas.
Prof. A. El- Sahn
The Crown
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.
Prof. A. El- Sahn
al Aspect
The Crown
Contact areas:
The al cusp is long and sharp, and looks much like a maxillary canine from the al aspect.
The tip of the al cusp is, in most cases, located a little mesial to the center of the crown ally, similar to the mandibular canine to a greater degree.
Prof. A. El- Sahn
al Aspect
The Crown
Occlusal outline:
The al cusp is longer and more pointed that the al cusp on mandibular second premolars.
Prof. A. El- Sahn
al Aspect
The Crown
The Crown
The mesial cusp ridge is shorter than the distal cusp ridges.
Either cusp ridges (or slopes) usually show shallow notches (concavities) of unworn teeth.
Prof. A. El- Sahn
al Aspect
The Crown
The notches on the mesial cusp ridges are more pronounced.
These notches serve as spillways for food during mastication and are sometimes called Thomas notches.
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Prof. A. El- Sahn
Morphology of the al surface:
The al surface of the crown is markedly convex (more than in maxillary premolars), especially at the cervical and middle thirds.
Prof. A. El- Sahn
al Aspect
The Crown
The Crown
There is a continuous ridge from the cervical margin to the cusp tip, which is called the al ridge (it is not as prominent as that on the maxillary first premolar).
Prof. A. El- Sahn
al Aspect
The Crown