Mandibular Premolars

AnatomyAnatomy
of Mandibularof Mandibular
PremolarsPremolars
Howard Chi, D.M.D.

Learning ObjectivesLearning Objectives
Anatomy of the mandibular premolars

Type Traits Of MandibularType Traits Of Mandibular
PremolarsPremolars
1. A 2-cusp type with 1 lingual cusp
2. A 3-cusp type with 2 lingual cusps

Distinguishing Characteristics OfDistinguishing Characteristics Of
Mandibular PremolarsMandibular Premolars
Generally speaking :
1. The mand. 1st premolar has
a longer crown and a shorter
root than the 2nd premolar
2. The mand. 1st premolar is
longer overall than the 2nd
2nd 1st

Buccal Aspect OfBuccal Aspect Of
1. Crown Shape: (roughly
pentagonal)
 1st: Nearly symmetrical except for
a shorter mesial cusp ridge and a
distal bulge of the crown

Buccal Aspect OfBuccal Aspect Of
1. Crown Shape: (roughly
pentagonal)
2nd premolar: Buccal cusp is
less pointed and cusp slopes
are less steep than on the
mandibular 1st premolar
2nd 1st

2nd 1st
Buccal AspectBuccal Aspect
2. Notches on Cusp Ridges:
 Notches often seen on
mesiobuccal cusp ridge in
mandibular 1st premolars
 Notches often seen on
distobuccal cusp ridge in
mandibluar 2nd premolars

3. Cervical Lines:
The cervical line of the
mandibular 1st premolar
is more rounded
mesiodistally, while that of
the 2nd premolar is more
flat
2nd 1st

4. Contact Areas - Mesial:
1st and 2nd premolar - near
junction of occlusal and
middle third

5. Contact Areas - Distal:
1st premolar distal contact
area is more OCCLUSAL
than the mesial contact area
(an exception to the rule)

6. Contact Areas - Distal:
2nd premolar has a
distal contact located
more cervical than the
mesial contact area, as is
usually the case with
posterior teeth

Lingual Aspect Of MandibularLingual Aspect Of Mandibular
PremolarsPremolars
1. Crown Shape:
Mandibular first
premolar crown tapers
(converges) to the lingual
(narrower on lingual side
that buccal)

Lingual Aspect Of MandibularLingual Aspect Of Mandibular
PremolarsPremolars
1. Crown Shape:
 Mandibular 2nd premolar with 1
lingual cusp, crown tapers to
lingual
 Mandibular 2nd premolar with 2
lingual cusps, crown is as wide or
wider mesiodistally than the
buccal

Lingual AspectLingual Aspect
2. Cusp Size and Shape:
 Mandibular 1st premolar
lingual cusp is small and
pointed
 Most of the occlusal surface
can be seen from this aspect
M D

 Mandibular 2nd premolar
with 1 lingual cusp:
 Lingual cusp is smaller than
buccal cusp, but larger than
lingual cusp of 1st premolar
M D

 Mandibular 2nd premolar with
2 lingual cusps:
 ML cusp is larger than the DL
cusp, with the L groove
between them and onto the
lingual crown surface
ML DL
M D

3. Marginal Ridges:
Mandibular 1st premolar:
Only tooth in the mouth
where the mesial marginal
ridge is more apical than the
distal marginal ridge
M D

3. Marginal Ridges:
Mandibular 2nd premolar:
Mesial marginal ridge is
more occlusal than the distal
marginal ridge (as found in
all other teeth)
M D

4. Mesiolingual Groove:
Frequently seen on
Mandibular 1st
premolar only

Proximal Aspect Of MandibularProximal Aspect Of Mandibular
PremolarsPremolars
1. Crown Shape - Rhomboid:
The crowns of both
premolars tilt lingually,
but the mandibular 1st
premolar tilts more
lingually than the
mandibular 2nd premolar
Mesial View

Proximal Aspect Of MandibularProximal Aspect Of Mandibular
PremolarsPremolars
1. Crown Shape -
Rhomboid:
In both premolars, the
lingual cusps are
shorter than the buccal
cusps
Mesial View

Proximal AspectProximal Aspect
2. Mesiolingual Groove:
 Often present on Mandibular 1st
premolar between the mesial
marginal ridge and the mesial slope
of the lingual cusp
 Not present on Mandibular 2nd
premolars

3. Height of Contour:
Mandibular 1st premolar
Buccal = cervical 1/3
Lingual = middle 1/3

3. Height of Contour:
Mandibular 2nd premolar
Buccal = junction of cervical
and middle 1/3
Lingual = middle 1/3

4. Cervical Lines:
Both premolars have
greater curve on the
mesial than the distal
Mesial
Distal

5. Root (proximal):
Both premolars generally
consist of one root
The mandibular 1st
premolar occasionally will
have a furcated root

6. Root Depressions:
Mandibular 1st premolar:
Have a shallow root
depression in the apical and
middle thirds of both mesial
and distal root surfaces
Mesial
Distal

6. Root Depressions:
Mandibular 2nd premolar:
Have a distal root depression in
the middle third of the root, but
NO mesial depression
Mesial
Distal

Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular
First PremolarFirst Premolar
1. Outline:
– Have much variation in
occlusal morphology
– Outline is not symmetrical
(more bulky on the distal)
DM

1. Outline:
– Often appears as if the mesial
side has been pushed inward
(mesiolingual corner)
DM

1. Outline:
– Tip of the buccal cusp
is near the center from
occlusal view
– Lacks a prominent
buccal ridge
– Cusp ridges are nearly
straight lines
DM

1. Outline:
– Crown is somewhat
diamond shaped
converging lingually
– Shape of crown is
asymmetrical DM

1. Outline:
– Mesial and distal
marginal ridges may
converge lingually

2. Ridges, Fossae, Grooves:
– Due to size of cusp, the
buccal triangular ridge
is long
– Joins the shorter lingual triangular ridge
– Often may meet smoothly and form a uninterrupted
transverse ridge

– The transverse ridge
may be crossed by
a shallow central groove
extending from mesial to distal fossa
– This is rare

– The grooves of the first premolar are fewer in
number, but may be deeper than those of the
second premolar (just like the maxillary)

– Possess a mesial
and distal fossa
– Both are circular,
not triangular
– Both possess pits
– Distal fossa is usually larger and/or deeper
D

Second PremolarSecond Premolar
1. Outline - Two-cusp version:
– Crown is round or oval
shaped with a square
occlusal table

1. Outline - Two-cusp version:
– There is slightly more bulk in
the mesial half buccolingually
than in the distal half

2. Ridges, Fossae, Grooves - Two-cusp version:
– Lingual cusp smaller than
buccal cusp
– Possess more supplemental
grooves than first premolars
– Also has a smaller triangular
ridge

2. Ridges, Fossae, Grooves - Two-cusp version:
Possess a curved central
groove with no lingual
groove
This groove can be fairly
straight
D

1. Outline - Three-cusp version:
– When lingual cusps are
large, the occlusal
surface is broader on the
lingual

1. Outline - Three-cusp version:
Often have greater bulk buccolingually in the
distal not the mesial
The ML cusp is usually
larger than the DL cusp
ML DL

2. Ridges, Fossae, Grooves - Three-cusp version:
Possess three triangular
ridges converging toward
the central fossa
There is no transverse ridge
1
2 3

Has a central fossa
(unique) shifted
towards the distal
Lacks a central groove
Mesial groove present
M
C
D

 Possess a lingual groove
that separates the two
lingual cusps
 This groove completes
the Y-shaped occlusal
groove pattern

Mandibular Premolars

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