1
Q
Mesiodistal Crown Width
A
- The mesiodistal
crown width is
greatest on first
molars and less
on second molars. - Most of the experts
say that third molars
are smaller mesiodistally
than second
molars, a couple say
they are the same,
and one says that
third molars are
actually larger than
second molars. - Due to the
variability in
the size of third
molars, all of
these are true
possibilities.
2
Q
Occlusocervical Crown Height
A
- Some of the
experts say that
the occlusocervical
crown
height is greatest
on first molars and
less on second
molars. - Others say they
are the same, and
still others say that
the crown height of
the second molar
is actually greater
than the first. - Likewise, there is
disagreement about
third molars, where
some experts say
they are shorter
than second molars
and others say they
are the same. - In fact all of
these are true
possibilities.
3
Q
Crown Symmetry
A
- Second molars are
more symmetric
than first molars
(second molars
don’t have a distal
cusp).
4
Q
Third Molar Distal Crown Height
A
- The distal half of
third molar crowns
is noticeably
shorter occlusocervically
than the mesial half.
5
Q
Number of Buccal Cusps
A
- First molars have
3 buccal cusps
whereas second
and third molars
usually have only
2 buccal cusps. - Second and
third molars will
occasionally have
3 buccal cusps and
will look like small
first molars.
6
Q
Occlusocervical Cusp Height and Form
A
- Second molar
cusps are taller
and more pointed
than the shorter,
blunted first molar
cusps.
7
Q
Number of Buccal Grooves
A
- First molars have
2 buccal grooves
whereas second
and third molars
usually have only
1 buccal groove.
8
Q
Root Length
A
- First molars have
longer roots than
second molars.
Second molars
have longer roots
than third molars.
9
Q
Root Separation
A
- The greatest
mesiodistal root
separation is on
first molars, less
on second molars,
and the least
separation (even
fusion) on third
molars.
10
Q
Root Parallelism
A
- The roots are
more parallel to
one another on
second molars
than first molars.
11
Q
Root Apex Curvature
A
- The mesial root
is usually curved
to the distal on
first molars,
and sometimes
strongly curved in
the apical one third.
12
Q
Root Trunk Dimensions
A
- The cervico-apical
dimension (height)
of the root trunk is
greatest on third
molars, less on
second molars,
and is the shortest
on first molars.
13
Q
Root Inclination
A
- The distal
inclination of the
roots is greatest on
third molars, less
on second molars,
and the least distal
inclination occurs
on first molars.
14
Q
Root Apex Form
A
- Second molars
have more pointed
root apices than
first molars.
15
Q
Buccolingual Crown Width
A
- When viewed
occlusally, the
buccolingual
width is greatest
on first molars
and less on
second molars. - Third molars
may be narrower,
wider, or the
same as second
molars.
16
Q
Crown Outline Shape
A
- From an occlusal
view, crowns of
first molars are
pentagonal in
shape whereas
second molars
are more
rectangular. - Third molars
are rectangular
or ovoid.
17
Q
Mesiobuccal Prominence
A
- There is a
mesiobuccal
prominence
when second
molars are
viewed
occlusally.
18
Q
Crown Form Variations
A
- Third molars
vary from their
“normal” form
more often than
other teeth. - One common
variation is an
extra-large crown
with short, poorly
formed roots. - The existence
of the extra-large
crown probably
accounts for
some of the
expert’s disagreements
about the sizes
of these teeth.
19
Q
Proximal Crown Form
A
- From an occlusal
view, the mesial
and distal
surfaces of
first molars are
straighter than
the corresponding
surfaces on
second molars. - Comparing
second molars
to third molars,
third molar
surfaces would
be more convex. - For each individual
tooth the mesial
surface would be
straighter (flatter)
than its distal
surface, a remnant
of the evolution of
mammalian teeth
from their reptile
ancestors.
20
Q
Proximal Crown Convergence
A
- The crown
tapers lingually
more on first
molars than
second molars.
21
Q
Number of Cusps
A
- Mandibular first
molars usually
have 5 cusps
whereas second
and third molars
usually have 4
cusps. - Five-cusp
third molars
are common,
however, and
they may
occasionally
have more
than 5 cusps. - If you find 5-cusp
third molars in
your extracted
teeth next week,
save them for
mounting, do
not cut them up.
22
Q
Central Developmental Groove Form
A
- The central
developmental
groove has a
“zigzag” mesiodistal
form on first molars
whereas it is
straighter on
second molars.
23
Q
Developmental Groove Alignment
A
- The buccal
and lingual
developmental
grooves are not
aligned with each
other on the first
molar whereas
they are aligned
on second molars. - Anthropologists
have referred to
the pattern on
first molars as
“Y 5” and the
pattern on second
molars as “+ 4”. - There is no set
pattern on third
molars, as they
may resemble
either first or
second molars.
24
Q
Supplemental Grooves
A
- Second molars
generally have
more supplemental
grooves than first
molars, and third
molars have more
supplemental
grooves than
second molars. - It’s not uncommon
for third molars
to have many
supplemental
grooves, and
a “wrinkled”
occlusal surface.
25
Buccolingual Cusp Proximity
* The buccal and
lingual cusps of
third molars are
closer to each
other than the
cusps of the
other molars.
* Third molars
therefore have a
smaller occlusal
table than first or
second molars.
26
Crown Form
* Third molars
have more
bulbous crowns
than first or
second molars.
27
Buccolingual Root Width
* The buccolingual
width of
the mesial root
is greater on
first molars than
second molars.
