口腔解剖生理学之国外PPT--MANDIBULAR FIRST PREMOLAR(下颌4)
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Prof. A. El- Sahn
The Mesial Aspect
The Crown
The tip of the short lingual cusp is usually in line vertically with the lingual border of the cervical portion of the root.
Prof. A. El- Sahn
This differs from the condition found in maxillary posterior teeth, where both buccal and lingual cusp tips are well within the confines of the root trunks.
The Mesial Aspect
The Crown
The geometric outline of the crown proximally is roughly rhomboidal as all mandibular posterior teeth.
Prof. A. El- Sahn
The Mesial Aspect
The Crown
The lingual cusp is always small, short, reaching about two-thirds the length of the crown and often has a pointed tip. Prof. A. El- Sahn
The Lingual Aspect
Buccal Aspect
The Crown
Vertical developmental depressions are often seen in the occlusal third of the buccal surface on either side of the buccal ridge (between the three buccal lobes).
D
M
Prof. A. El- Sahn
The Lingual Aspect
The Crown
Cervically
The cervical portion of the crown lingually is narrow and convex.
The cervical line is slightly convex towards the root.
D
The Root
M
The apical third of the root is often bent distally and sometimes mesially. The root of this tooth is shorter than that of the lower canine. Prof. A. El- Sahn
Prof. A. El- Sahn
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.
Prof. A. El- Sahn
Buccal Aspect
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
The cervical line:
Is slightly convex towards the root.
Prof. A. El- Sahn
Buccal Aspect
The single root is convex on its buccal surface and tapers gradually to a near - ly pointed apex.
The Crown
L
L
The crown is tilting lingually much more than any other premolar. So, the tip of the buccal cusp is nearly centered over the root. Prof. A. El- Sahn
Prof. A. El- Sahn
The Lingual Aspect
The Root
The root is much narrower on the lingual surface than on the buccal surface. It tapers from the cervix to a pointed apex. Prof. A. El- Sahn
MANDIBULAR FIRST PREMOLAR
Prof. A. El- Sahn
CHRONOLOGY
Initial Calcification Completion of Crown Eruption
1¾ – 2 years
5 – 6 years
10 – 12 years
Completion of Root
Prof. A. El- Sahn
Buccal Aspect
The Crown
Contact areas:
Prof. A. El- Sahn
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 Crown
Much of the occlusal surface of this tooth can be seen from the lingual aspect because of the shortness of the lingual cusp. Prof. A. El- Sahn
The curvature of the distal contact area is broader than that of the mesial one.
Buccal Aspect
The Crown
Occlusal outline:
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.
M
D
Prof. A. El- Sahn
The Lingual Aspect
The Crown
There is a mesio-lingual developmental groove separating the mesial marginal ridge from the mesial slope of the small lingual cusp. This groove acts as a line of demarcation between the mesio-buccal lobe and the lingual lobe and extends into the mesial fossa of the occlusal surface.
Prof. A. El- Sahn
Buccal Aspect
The Crown The Crown
The buccal cusp is longer and more pointed that the buccal cusp on mandibular second premolars.
Prof. A. El- Sahn
The Mesial Aspect
The Crown
B
The lingual cusp is shorter than the buccal cusp by about one third of the crown length, which is from the cervical line buccally to the tip of the buccal cusp.
Prof. A. El- Sahn
The Lingual Aspect
The Crown
The tip of the lingual cusp is in alignment with the triangular ridge of the buccal cusp. The mesial and distal occlusal fossae are on each side of the triangular ridge.
12 – 13 years
Prof. A. El- Sahn
Buccal Aspect
The Crown
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.
Buccal Aspect
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
Cervically, the crown is narrower mesio-distally than at the contact areas. Prof. A. El- Sahn
Buccal Aspect
The Crown
The Lingual Aspect
The Crown
The crown tapers lingually, so the lingual side is narrower than the buccal side. Prof. A. El- Sahn
The Lingual Aspect
2\3
D M
Prof. A. El- Sahn
Buccal Aspect
The Crown The Crown
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.
源自文库
The Lingual Aspect
The Crown
The mesial and distal outlines are slightly concave between the cervical line and the contact areas. The contact areas and marginal ridges are pronounced and extend out above the narrow cervical portion of the crown.
The Mesial Aspect
The Crown
The tip of the short lingual cusp is usually in line vertically with the lingual border of the cervical portion of the root.
Prof. A. El- Sahn
This differs from the condition found in maxillary posterior teeth, where both buccal and lingual cusp tips are well within the confines of the root trunks.
The Mesial Aspect
The Crown
The geometric outline of the crown proximally is roughly rhomboidal as all mandibular posterior teeth.
Prof. A. El- Sahn
The Mesial Aspect
The Crown
The lingual cusp is always small, short, reaching about two-thirds the length of the crown and often has a pointed tip. Prof. A. El- Sahn
The Lingual Aspect
Buccal Aspect
The Crown
Vertical developmental depressions are often seen in the occlusal third of the buccal surface on either side of the buccal ridge (between the three buccal lobes).
D
M
Prof. A. El- Sahn
The Lingual Aspect
The Crown
Cervically
The cervical portion of the crown lingually is narrow and convex.
The cervical line is slightly convex towards the root.
D
The Root
M
The apical third of the root is often bent distally and sometimes mesially. The root of this tooth is shorter than that of the lower canine. Prof. A. El- Sahn
Prof. A. El- Sahn
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.
Prof. A. El- Sahn
Buccal Aspect
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
The cervical line:
Is slightly convex towards the root.
Prof. A. El- Sahn
Buccal Aspect
The single root is convex on its buccal surface and tapers gradually to a near - ly pointed apex.
The Crown
L
L
The crown is tilting lingually much more than any other premolar. So, the tip of the buccal cusp is nearly centered over the root. Prof. A. El- Sahn
Prof. A. El- Sahn
The Lingual Aspect
The Root
The root is much narrower on the lingual surface than on the buccal surface. It tapers from the cervix to a pointed apex. Prof. A. El- Sahn
MANDIBULAR FIRST PREMOLAR
Prof. A. El- Sahn
CHRONOLOGY
Initial Calcification Completion of Crown Eruption
1¾ – 2 years
5 – 6 years
10 – 12 years
Completion of Root
Prof. A. El- Sahn
Buccal Aspect
The Crown
Contact areas:
Prof. A. El- Sahn
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 Crown
Much of the occlusal surface of this tooth can be seen from the lingual aspect because of the shortness of the lingual cusp. Prof. A. El- Sahn
The curvature of the distal contact area is broader than that of the mesial one.
Buccal Aspect
The Crown
Occlusal outline:
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.
M
D
Prof. A. El- Sahn
The Lingual Aspect
The Crown
There is a mesio-lingual developmental groove separating the mesial marginal ridge from the mesial slope of the small lingual cusp. This groove acts as a line of demarcation between the mesio-buccal lobe and the lingual lobe and extends into the mesial fossa of the occlusal surface.
Prof. A. El- Sahn
Buccal Aspect
The Crown The Crown
The buccal cusp is longer and more pointed that the buccal cusp on mandibular second premolars.
Prof. A. El- Sahn
The Mesial Aspect
The Crown
B
The lingual cusp is shorter than the buccal cusp by about one third of the crown length, which is from the cervical line buccally to the tip of the buccal cusp.
Prof. A. El- Sahn
The Lingual Aspect
The Crown
The tip of the lingual cusp is in alignment with the triangular ridge of the buccal cusp. The mesial and distal occlusal fossae are on each side of the triangular ridge.
12 – 13 years
Prof. A. El- Sahn
Buccal Aspect
The Crown
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.
Buccal Aspect
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
Cervically, the crown is narrower mesio-distally than at the contact areas. Prof. A. El- Sahn
Buccal Aspect
The Crown
The Lingual Aspect
The Crown
The crown tapers lingually, so the lingual side is narrower than the buccal side. Prof. A. El- Sahn
The Lingual Aspect
2\3
D M
Prof. A. El- Sahn
Buccal Aspect
The Crown The Crown
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.
源自文库
The Lingual Aspect
The Crown
The mesial and distal outlines are slightly concave between the cervical line and the contact areas. The contact areas and marginal ridges are pronounced and extend out above the narrow cervical portion of the crown.