Mandibular First Molar Flashcards
1
Q
3 Buccal Cusps
A
- 1 - Mesiobuccal
- 2 - Distobuccal
- 3 - Distal
2
Q
Mesiobuccal cusp
A
- The mesiobuccal cusp
is the largest, widest,
and tallest of the three
buccal cusps. - As a stamp cusp
(supporting cusp,
occluding cusp) it
may be rather blunt. - In width it occupies
just slightly less than
half of the mesiodistal
crown dimension.
3
Q
Distobuccal Cusp
A
- The distobuccal cusp
may be sharper than
the mesiobuccal cusp
(55% of the time) but
it’s still blunt compared
to the lingual cusps.
4
Q
Distal Cusp
A
- The small distal cusp
(which is really one of
three buccal cusps) is
present 81% of the time
and is sharper than the
other buccal cusps. - 81% seems low; it
should be around 90%.
5
Q
Lingual cusp visibility
A
- The two lingual cusps
(mesiolingual and
distolingual) are visible
because they are taller
than the buccal cusps.
6
Q
Buccal Cusp Form
A
- The buccal cusps
are relatively flat
compared to the
taller and sharper
lingual cusps. - The buccal cusps of
mandibular posterior
teeth (and the lingual
cusps of maxillary
posterior teeth) are
supporting or stamp
cusps and will be
blunter than the nonsupporting
cusps.
7
Q
Mesiobuccal groove
A
- The mesiobuccal
groove has been
described as longer
than the distobuccal
groove (70% of the
time) but are drawn
the same here. - This groove is often
deep and may become
carious through its
entire length. - There may be a deep
pit at its cervical end,
which is at the
occlusocervical
center of the crown. - The pit is positioned
a little mesial to the
furcation and mesial
to the mesiodistal
center of the tooth. - The pit frequently
becomes carious, and
it may become carious
independent of the
groove.
8
Q
Distobuccal groove
A
- The distobuccal
groove terminates at
the distobuccal line
angle. - The distobuccal groove
has a distal inclination
and it parallels the long
axis of the distal root. - The groove can extend
most of the length of
the buccal surface or
it can be very short. - Like the mesiobuccal
groove it may also be
deep and carious,
but this is much less
frequent than in the
mesiobuccal groove. - Occasionally there is
also a pit at its cervical
end which may become
carious.
9
Q
Mesial Crown Outline
A
- The mesial outline is
slightly concave or
nearly straight from
the mesial proximal
contact to the cervical
line.
10
Q
Cervical line form
A
- The buccal cervical
line is nearly straight
but the enamel can
dip cervically, nearly
into the furcation. - The dip may be sharp
and this is frequently
the location of an
enamel pearl.
11
Q
Distal Crown Outline
A
- The distal outline is
more convex than the
flatter mesial outline.
12
Q
Buccal cervical ridge
A
- Sometimes there
is a fairly prominent
enamel ridge running
mesiodistally in the
gingival (cervical)
third, called the buccal
cervical ridge or
buccogingival ridge. - If present, the buccal
height of contour will
be on this ridge. - The height of contour
will still be located in
the cervical third even
if a prominent ridge is
not present.
13
Q
Horizontal developmental depression
A
- A developmental
depression may be
present in the middle
third of the crown
at the level of the
termination of the
buccal developmental
grooves. - If present it runs
mesiodistally along
the occlusal border
of the buccal cervical
ridge.
14
Q
Root Lengths
A
- The mesial root is
longer than the distal
root by about 1 mm.
15
Q
Root form
A
- The distal root is
straighter than the
mesial root.
16
Q
Root orientation
A
- The mesial root is
twisted on the root
trunk in such a way
that it is frequently
possible to see its
distal surface.
17
Q
Root apex form
A
- The distal root apex
may be more pointed
than the mesial root
apex (not shown in
the drawing).
18
Q
Root curvature
A
- The mesial root curves
mesially to its middle
third and then curves
distally. - One expert says
the apex of the
mesial root may be
located beneath the
mesiobuccal groove
(shown). - Another says the
apex of the mesial
root is directly in line
with the mesiobuccal
cusp (not shown,
but either location is
possible, dependent
on the curvature of the
mesial root).
19
Q
Root bifurcation/Root trunk
A
- The root bifurcation
begins near the
cervical line with a
depression existing
between the cervical
line and furcation. - The root trunk is
relatively short (shortest of 3) - The point of complete
bifurcation is located
approximately 3 mm
apical to the cervical
line.
20
Q
Root separation
A
- The root apices are
widely separated.
21
Q
Overall root inclination
A
- Both roots have
an overall distal
inclination. - The wide separation
and distal inclination
makes this tooth
difficult to extract.
22
Q
Mesial root extension
A
- The mesial surface of
the mesial root may
extend mesially beyond
the cervical line, but
not as far as the mesial
surface of the crown.
23
Q
Distal root extension
A
- The distal root apex
may extend distally
beyond the distal
surface of the crown.
24
Q
Lingual crown convergence
A
- Since the greatest
mesiodistal crown
width is located
buccally, portions of
the proximal surfaces
are visible from a
lingual view (best viewed
in occlusal view).
25
Cusp height & visibility
* The two lingual cusps
have been described as
approximately equal in
height, and alternately
with the mesiolingual
being slightly taller
than the distolingual.
* In any case both lingual
cusps are taller than the
buccal cusps, hiding
the mesiobuccal and
distobuccal cusps from
view.
* However, the lingual
aspect of the distal
cusp can be seen.
26
Lingual cusp dimension
* The mesiodistal width
of the mesiolingual
cusp is often slightly
greater than the
distolingual cusp
(58% of 256 teeth).
27
Lingual cusp form
* The lingual cusps
possess similar
sharpness.
* The cusp ridges form
obtuse angles of about
100 degrees, more
pointed than the
flatter buccal cusps.
28
Lingual groove
* The lingual groove
may terminate on the
occlusal surface or it
may extend onto the
lingual surface in the
occlusal third (shown).
* The lingual surface can
be slightly concave or
deeply notched in its
center by the lingual
groove.
* If the groove extends
onto the lingual surface
it will be shallower than
the buccal grooves and
unlike the buccal
grooves it’s almost
never carious.
* The Tooth Atlas says it
may terminate in a pit,
but that’s extremely
rare.
29
Cervical line form
* The lingual cervical line
is nearly straight but
there can be enamel
that dips cervically in
the center.
30
Lingual root convergence
* The roots taper lingually.
* The lingual root taper
combined with the
twisting of the root on
the root trunk make it
possible to see the
mesial surface of the
mesial root and/or the
distal surface of the
distal root.
31
Root trunk form
* The root trunk has a
groove or depression
between the cervical
line and the root
bifurcation.
* The depression is
almost in line with the
lingual developmental
groove.
32
Root trunk dimension
* The root trunk has a
greater height on the
lingual surface than on
the buccal because the
cervical line is located
further occlusally on
the lingual.
* The distance from
the cervical line to
the bifurcation is one
millimeter greater on
the lingual surface
(4 mm on the lingual,
3 mm on the buccal).
33
Crown Dimensions
* The mesiodistal
crown width is
greater than the
buccolingual
width.
* The average
difference is
as great as 1.2
millimeters and
as small as 0.5
millimeter.
* The mandibular
first molar is
normally the
largest tooth
in the arch.
34
Buccolingual crown width
* The greatest
buccolingual
width is at the
distobuccal cusp.
35
Crown outline
* The outline has
traditionally been
described as
pentagonal.
* The outline
has also been
described as
hexagonal.
* The angles
between the buccal
surface and the
proximal surfaces
are about equally
acute and the
lingual angles
are obtuse.
36
Buccal surface visibility
* More of the buccal
surface is visible
than the lingual
surface.
* At least two-thirds
of the buccal
surface is visible
but only the
occlusal third of
the lingual surface
due to the lingual
tilt of the crown.
37
Lingual crown convergence
* The crown tapers
lingually, thereby
having a narrower
mesiodistal width
on the lingual
surface.
38
Distal crown convergence
* The crown
tapers distally,
thereby producing
a narrower buccolingual
width on
the distal aspect
of the crown.
39
Mesial proximal contact
* The buccolingual
position of the
mesial proximal
contact has been
traditionally
located buccal to
the crown center.
* It has also been
located at about
the buccolingual
center.
40
Buccal cusp segments
* The buccal cusp
profile is divided
into 3 distinct and
separate convex
segments.
* The mesiodistal
width of
each segment
decreases from
mesial to distal.
41
Distal proximal contact
* (Three different
locations have
been described)
* The buccolingual
position of the
distal proximal
contact has been
located buccal to
the crown center
(the traditional
location), over the
center of the root, and just lingual
to the distal cusp.
* The contact is
variable because
the location of
the distal cusp
varies.
* The contact is
also dependent
on the position of
the second molar,
which is variable.
42
Lingual surface form
* The lingual surface
is nearly straight.
43
Cusp sizes
* The relative sizes
of the five cusps
(when viewed
occlusally) have
been listed in the
following order
from largest to
smallest:
* Mesiobuccal
* Two lingual cusps
which are almost
equal in size, with
the mesial being
slightly larger
* Distobuccal
* Distal
* The distal features
of the posterior
teeth are generally
smaller, rounder,
and less wellformed,
a remnant
of their more
recent evolution
from reptile teeth.
44
Cusp height
* The height of the
five cusps has
been listed in the
following order
from tallest to
shortest:
* Mesiolingual
* Distolingual
* Mesiobuccal
* Distobuccal
* Distal
* The mesiobuccal
and distobuccal
cusps are
approximately
equal in height
with the mesial
being slightly
taller.
45
Fossae
* There are three
fossae: central,
mesial, and distal.
46
"Transverse Ridges"
* The Tooth Atlas
says that the
triangular ridges of
the mesiobuccal
and mesiolingual
cusps meet to form
a transverse ridge.
* The Tooth Atlas
also says that the
triangular ridges
of the distobuccal
and distolingual
cusps meet to form
a transverse ridge.
* Traditionally, it
has been accepted
that there are NO
transverse ridges
on the first molar
due to the strong
central groove.
47
Triangular ridge length
* Since the lingual
cusps are taller
than the buccal
cusps, the lingual
triangular ridges
*should be longer*.
* It has also been
stated that the
triangular ridge
of the distobuccal
cusp is the longest
of the ridges,
extending into the
lingual groove.
48
Developmental grooves
* There are four
developmental
grooves on the
occlusal surface:
* Central
* Mesiobuccal
* Distobuccal
* Lingual
49
Central groove form
* The central
developmental
groove has a
zigzag mesiodistal
form.
* It has been
described as a
“W” and as an “M”
depending on the
viewing direction.
* The central
developmental
groove forms a
“Y” shape with
the other
developmental
grooves.
* The “Y-5” form
(Y-shaped groove
and 5 cusps) of
mandibular molars
is an important
evolutionary
landmark between
monkeys and
hominids (us).
* The 5-cusp
mandibular
first molar has
persisted to this
day in the Apes
and in Man.
50
Crown outline
* The outline of
the crown has
been described
as rhomboidal.
51
Cusp form
* The lingual cusps are
taller and more pointed
than the buccal cusps
(more pointed not
shown).
52
Marginal ridge groove
* The mesial marginal
ridge usually has a
groove crossing the
ridge.
* When 209 teeth were
evaluated, 68% had
marginal ridge grooves.
* This groove is rarely
defective and is not
comparable to the
prominent mesial
marginal ridge groove
on the maxillary 1st
premolar.
53
Buccal height of contour
* The buccal height
of contour has been
located in the cervical
third of the crown.
54
Cervical line location
* The buccal cervical
line is located farther
cervically than the
lingual cervical line
(the lingual root trunk
is longer than the
buccal root trunk).
55
Lingual height of contour
* The lingual height
of contour is located
in the middle third,
but frequently near
the junction with
the occlusal third
(shown).
* The actual
measurement of
the lingual height of
contour (1 mm in the
mandibular molars)
is the largest of any
teeth in the mouth.
56
Buccolingual root width
* The wide buccolingual
dimension of the mesial
root prevents the distal
root from being visible.
* The buccolingual
width of the mesial
root is twice its mesiodistal
width.
57
Root surface form
* Both the mesial and
distal surfaces of the
mesial root have
depressions.
* The depression is deep
on the mesial surface
and even deeper on the
distal (not visible in any
of the views).
* Because of these deep
depressions the mesial
root always has two
root canals.
58
Marginal ridge location
* The distal marginal
ridge is located cervical
to the mesial marginal
ridge.
* More of the occlusal
surface is visible from
a distal view than the
mesial view because
the distal surface is
shorter occlusocervically.
59
Marginal ridge groove
* An extension of the
central developmental
groove quite often
crosses the distal
marginal ridge lingual
to the proximal contact
area.
* It is shorter than the
mesial marginal ridge
groove.
* On 215 molars, 48%
had this groove.
60
Buccolingual root width
* The distal root is not as
wide as the mesial root.
* The lingual border of the
mesial root may be seen
from a distal view.
61
Root surface form
* The distal root may
have developmental
depressions on both
the mesial and distal
surfaces.
* The mesial surface
of the distal root (not
visible) is more likely
to have a depression
and it is more likely
to be deeper than the
distal depression.
* As a result, the distal
root may also have two
canals (approximately
10% of the time).
* The mesial root had two
canals 100% of the time.
