口腔解剖生理学之国外--下颌第三磨牙PPT演示幻灯片

resembles that of the lower second
ቤተ መጻሕፍቲ ባይዱ
molars in the number of cusps (four
cusps) and sometimes resembles the
crown of the lower first molar (five
cusps) or it may bear little resemblance
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BUCCAL ASPECT
THE CROWN
The mesio-buccal cusp is the widest and usually highest of the two or three buccal cusps.
The buccal surface is very convex.
Prof. A. Elsahn 10
Prof. A. Elsahn
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BUCCAL ASPECT
THE ROOTS
If the roots are separated, the root
trunk is long and the roots are
usually more pointed at the apex
than on other molars.
Prof. A. Elsahn
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LINGUAL ASPECT
THE CROWN
The proximal sides of the crown converge slightly lingually.
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BUCCAL ASPECT
THE CROWN
M
D
The mesial and distal outlines of the crown are generally as
those of all lower molars.
The distal outline is markedly
convex.
DESCRIPTIVE ANATOMY OF MANDIBULAR THIRD MOLAR
Prof. A. Elsah1n
CHRONOLOGY
Initial calcification 8 – 10 years
Completion of crown 12 – 16 years
Eruption
17 – 21 years
to either.
Prof. A. Elsahn 5
GENERAL CHARACTERISTICS
The third molar may be small or large.
In many cases, it is larger than the lower second molar.
Prof. A. Elsahn
It shows variations in size, form, number of cusps and number and form of roots.
Prof. A. El4sahn
GENERAL CHARACTERISTICS
The crown of this tooth in most cases
Completion of roots 18 – 25 years
Prof. A. El2sahn
GENERAL CHARACTERISTICS
The lower third molar is the last tooth in the dental arch and the eighth from the middle line.
It is the shortest of the mandibular teeth.
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4 3 12
Prof. A. El3sahn
GENERAL CHARACTERISTICS
This tooth is a very variable tooth, but less so than upper third molar.
BUCCAL ASPECT
THE ROOTS
M
D
This molar usually show two roots, one mesial and one distal.
Prof. A. Elsahn
11
:
1.6 : 1
BUCCAL ASPECT
THE ROOTS
These roots are usually shorter than those of first or second molars.
Prof. A. Elsahn
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BUCCAL ASPECT
THE CROWN
The crown is wider at the
contact area mesio-distally
than at the cervix.
M
D
Prof. A. Elsahn
The crest of contour mesially and distally is located a little more than half the distance from cervical line to cusp tips.
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BUCCAL ASPECT
THE CROWN
The buccal cusps are short and rounded.
In the four-cusp type; the molar is
small and shows two buccal cusps
only.
Prof. A. Elsahn
D
The roots are more inclined
distally than those of the first
and second molars.
Prof. A. Elsahn
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BUCCAL ASPECT
THE ROOTS
The roots may be separated or fused for all or part of their length.
The root to crown ratio is smaller than that of first and second molar (1.6 to 1 compared to 1.8 to 1).
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Prof. A. Elsahn
1.8
BUCCAL ASPECT
THE ROOTS
M
DM