Mandibular Second Molar

Question 1

Mesiobuccal cusp

Answer 1

• The mesiobuccal
  cusp has the greatest
  mesiodistal dimension
  66% of the time.

Question 2

Buccal developmental groove

Answer 2

• There is a single buccal
  developmental groove
  ending in the middle of
  the buccal surface.
• A pit may be present at
  the end of the groove,
  but the pit occurs less
  frequently than it does
  on the first molar, and
  it’s less likely to be
  carious.

Question 3

Mesial proximal contact

Answer 3

• The mesial proximal
  contact has been
  located at the junction
  of the occlusal and
  middle thirds (drawn
  too far occlusally).
• It has also been
  noted that this
  contact is positioned
  further cervically than
  the mesial contact of
  the first molar (the
  normal progression).

Question 4

Distal proximal contact

Answer 4

• The distal proximal
  contact has been
  described as centered
  occlusocervically in
  the middle third.
• This is located cervical
  to the mesial proximal
  contact.

Question 5

Buccal cervical ridge

Answer 5

• The buccal cervical
  ridge (buccogingival
  ridge) is frequently
  prominent on second
  molars.
• It is more prominent
  mesially than distally.

Question 6

Root lengths

Answer 6

• The mesial root was
  longer than the distal
  root by an average of
  0.9 mm when measured
  on 296 teeth.
• Virtually the same as
  the first molar (mesial
  root was 1 mm longer).

Question 7

Root parallelism

Answer 7

• The root axes are
  nearly parallel.

Question 8

Root form

Answer 8

• The distal root has a
  tendency to be more
  nearly round (in cross
  section).
• The mesial root is more
  oval or even kidney
  bean-shaped (due to
  the distal depression.

Question 9

Root trunk dimension

Answer 9

• The root trunk is
  longer than the first
  molar root trunk.

Question 10

Root trunk form

Answer 10

• There is a depression
  on the root trunk from
  the cervical line to the
  furcation.

Question 11

Root separation

Answer 11

• The roots are not
  widely separated.

Question 12

Root curvature

Answer 12

• Both root apices
  frequently curve
  toward the midline
  of the tooth similar
  to the handles of a
  pair of pliers.
• Alternately both roots
  may curve distally.

Question 13

Proximal surface visibility

Answer 13

• Little if any of the
  mesial and distal
  surfaces are visible
  from the lingual since
  there is very little taper
  of the crown towards
  the lingual.

Question 14

Lingual cusp dimensions

Answer 14

• The lingual cusps are
  taller than the buccal
  cusps.
• The mesiolingual cusp
  is usually slightly wider
  mesiodistally than the
  distolingual cusp.

Question 15

Lingual cusp form

Answer 15

• Both lingual cusps
  possess similar
  sharpness.

Question 16

Lingual groove

Answer 16

• The lingual groove
  may terminate on the
  occlusal surface or
  it may extend onto the
  lingual surface in the
  occlusal third (shown).

Question 17

Buccolingual crown width

Answer 17

• The greatest
  buccolingual
  width is found in
  the mesial half at
  the location of the
  buccal cervical
  ridge.

Question 18

Crown outline

Answer 18

• The outline has
  been described
  as rectangular
  and also as
  nearly forming
  a parallelogram.
• This one is
  a rhombus.

Question 19

Mesiobuccal prominence

Answer 19

• There is a
  prominent bulge
  (buccal cervical
  ridge) on the
  mesiobuccal
  aspect of the
  crown.

Question 20

Distal outline

Answer 20

• The distal surface
  is more convex
  and rounded than
  the mesial surface
  which is nearly
  straight buccolingually.

Question 21

Lingual crown convergence

Answer 21

• The crown
  tapers lingually,
  making the crown
  slightly wider
  mesiodistally on
  the buccal aspect.

Question 22

Distal crown convergence

Answer 22

• The crown tapers
  distally.
• Neither taper is as
  much as it was in
  the first molar.

Question 23

Mesial proximal contact

Answer 23

• The buccolingual
  position of the
  mesial proximal
  contact has been
  located buccal to the
  center of the crown,
  near the junction of
  the buccal and
  middle thirds.

Question 24

Distal proximal contact

Answer 24

• The Tooth Atlas
  says that the
  buccolingual
  position of the
  distal proximal
  contact is located
  at the center of
  the crown.
• It is more often
  slightly offset to
  the buccal, which
  is the traditional
  location.

Question 25

Cusp size

Answer 25

• The mesiobuccal
  and mesiolingual
  cusps are
  generally a little
  larger than the
  distobuccal and
  distolingual cusps.
• The mesiobuccal
  cusp is normally
  the largest cusp
  and the distolingual
  the smallest.

Question 26

Cusp height

Answer 26

• The occlusal height
  of the 4 cusps has
  been listed in the
  following order from
  tallest to shortest:

1. Mesiolingual
2. Distolingual
3. Mesiobuccal
4. Distobuccal

Question 27

Buccal cusp ridges

Answer 27

• The cusp ridges
  of the distobuccal
  cusp are located
  buccal to the
  cusp ridges of the
  mesiobuccal cusp.

Question 28

Fossae

Answer 28

• There are 3
  fossae: mesial,
  central, and distal.

Question 29

“Transverse ridges”

Answer 29

• The Tooth Atlas says
  that the triangular
  ridges of the mesiobuccal
  and mesiolingual
  cusps and
  also the distobuccal
  and distolingual
  cusps meet to form
  transverse ridges.
• In the traditional
  definition we are
  using, these are
  not true transverse
  ridges due to the
  presence of a strong
  central groove.

Question 30

Developmental grooves

Answer 30

• There are 3
  developmental
  grooves:

1. Central
2. Buccal
3. Lingual

• The buccal and
  lingual grooves meet
  the central groove in
  such a manner that
  a “+” (plus) sign is
  formed, dividing
  the crown into four
  nearly equal parts.
• In Physical
  Anthropology
  and evolution
  this is called a
  “+ 4” pattern.

Question 31

Crown outline (mesial view)

Answer 31

• The outline has
  been described
  as rhomboidal.

Question 32

Buccal height of contour

Answer 32

• The buccal height
  of contour has been
  located in the cervical
  third of the crown.

Question 33

Lingual height of contour

Answer 33

• According to the Tooth
  Atlas the lingual height
  of contour is located in
  the middle third, but
  it’s sometimes located
  more occlusally, at the
  junction of the occlusal
  and middle third.
• Along with the
  mandibular first
  molar, this is the
  largest height of
  contour measurement
  of any tooth in the
  mouth (1 mm).

Question 34

Buccolingual root width

Answer 34

• The buccolingual
  width of the mesial
  root is greater than
  the distal root, thereby
  preventing the distal
  root from being visible.

Question 35

Root depressions

Answer 35

• Root depressions
  are common on both
  the mesial and distal
  surfaces of the mesial
  root, which gives this
  tooth two mesial canals
  approximately 98% of
  the time (first molar
  was 100% of the time).

Question 36

Marginal ridge location

Answer 36

• Typically, the
  distal marginal
  ridge is located
  farther cervically
  than the mesial
  marginal ridge.

Question 37

Bucolingual root width

Answer 37

• The distal root is
  narrower buccolingually
  than the
  mesial root.

Question 38

Root depressions

Answer 38

• A depression on
  the mesial surface
  of the distal root (not
  visible in this view)
  may cause the distal
  root to have two canals
  approximately 8% of
  the time (first molar
  was 10% of the time).