[医药卫生]口腔解剖生理学之国外PPT下颌第二磨牙

THE CROWN
CONTACT AREAS
MESIAL
Is at about the junction of the middle and occlusal thirds.
DISTAL Is at the center of the
middle third.
Prof. A. Elsahn
BUCCAL ASPECT
THE ROOTS
The root trunk is short (but slightly longer than on lower first molar).
There is a depression on the root trunk from the cervical line to the bifurcation.
mesio-buccal is usually wider.
M
D
The buccal developmental groove
separates the two buccal cusps, and
it may end in a pit on the middle of
the buccal surface.
Completion of roots 14 – 15 years
Prof. A. Elsahn
GENERAL CHARACTERISTICS
This molar is the seventh tooth from the middle line.
o It has four cusps.
Its disto-buccal cusp is larger than that found in the lower first molar.
outline: cervical line to the mesial
contact area.
Distal Is convex from the cervical outline: line to the distal contact area.
Prof. A. Elsahn
BUCCAL ASPECT
The cervical ridge is less pronounced than on
the first molars in most instances, but a
prominent bulge cervically on the mesio-buccal
cusp is common.
Prof. A. Elsahn
B 12
7
6 5 4 3
12
B
The crown is usually M 3 4 D
smaller than the first
L
molar in the same mouth.
D L
Prof. A. Elsahn
GENERAL CHARACTERISTICS
B
D
M
L
There is only one buccal groove.
DESCRIPTIVE ANATOMY OF MANDIBULAR SECOND MOLAR
Prof. A. Elsahn
CHRONOLOGY
Initial calcification 2½ – 3 years
Completion of crown 7 – 8 years
Eruption
11 – 13 years
OCCLUSAL OUTLINE
M
D
The two buccal cusps (mesio-buccal
and disto-buccal) and the tips of the
two lingual cusps (mesio-lingual and
Hale Waihona Puke disto-lingual) are visible from the
buccal side because the lingual cusps
are slightly longer.
Prof. A. Elsahn
BUCCAL ASPECT
THE CROWN
The two buccal cusps are about
equal mesio-distally but the
GENERAL CHARACTERISTICS
The root trunk is slightly longer than on the first molar.
The roots are as long (or may be longer), less broad bucco-lingually than on the first molar and are less widely separated or more parallel.
Prof. A. Elsahn
BUCCAL ASPECT
O
O
THE CROWN
D
C
M
C
D
As in the first molar,the crown is much larger mesiodistally than cervico-occlusally.
The crown appears to be wider at the cervix
than the first molar (less taper toward the
cervix below the contact areas), due to
absence of a distal cusp.
Prof. A. Elsahn
BUCCAL ASPECT
THE CROWN
M
D
Mesial Is nearly straight from the
Prof. A. Elsahn
BUCCAL ASPECT
THE CROWN
CERVICAL LINE
It is nearly straight.
It may point sharply toward the root bifurcation.
Prof. A. Elsahn
BUCCAL ASPECT
THE CROWN
Both contact areas are at slightly lower level, especially in the distal area than those of the first molar.
Prof. A. Elsahn
BUCCAL ASPECT
THE CROWN