口腔解剖生理学之国外--mandibularfirstpremolar(下颌4).pptVIP

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 Buccal 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 Buccal Aspect The Crown Contact areas: The buccal cusp is long and sharp, and looks much like a maxillary canine from the buccal aspect. The tip of the buccal cusp is, in most cases, located a little mesial to the center of the crown buccally, similar to the mandibular canine to a greater degree. Prof. A. El- Sahn Buccal Aspect The Crown Occlusal outline: The buccal cusp is longer and more pointed that the buccal cusp on mandibular second premolars. Prof. A. El- Sahn Buccal 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 Buccal 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. D M Prof. A. El- Sahn Morphology of the buccal surface: The buccal surface of the crown is markedly convex (more than in maxillary premolars), especially at the cervical and middle thirds. Prof. A. El- Sahn Buccal Aspect The Crown The Crown 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). Prof. A. El- Sahn Buccal Aspect The Crown Vertica