Mandibular Premolars
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Transcript of Mandibular Premolars
Anatomy Anatomy of Mandibularof MandibularPremolarsPremolars
Howard Chi, D.M.D.
Learning ObjectivesLearning Objectives
Anatomy of the mandibular premolars
Type Traits Of Mandibular Type Traits Of Mandibular PremolarsPremolars
1. A 2-cusp type with 1 lingual cusp
2. A 3-cusp type with 2 lingual cusps
Distinguishing Characteristics Of Distinguishing 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 Of Buccal Aspect Of Mandibular PremolarsMandibular Premolars
1. Crown Shape: (roughly pentagonal)
1st: Nearly symmetrical except for a shorter mesial cusp ridge and a distal bulge of the crown
Buccal Aspect Of Buccal Aspect Of Mandibular PremolarsMandibular Premolars
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 Aspect Buccal 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
Buccal AspectBuccal Aspect
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
Buccal AspectBuccal Aspect
4. Contact Areas - Mesial:
1st and 2nd premolar - near junction of occlusal and middle third
Buccal AspectBuccal Aspect
5. Contact Areas - Distal:
1st premolar distal contact area is more OCCLUSAL
than the mesial contact area
(an exception to the rule)
Buccal AspectBuccal Aspect
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 Mandibular Lingual 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 Mandibular Lingual 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
Lingual AspectLingual Aspect
2. Cusp Size and Shape:
Mandibular 2nd premolar with 1 lingual cusp:
Lingual cusp is smaller than buccal cusp, but larger than lingual cusp of 1st premolar
M D
2. Cusp Size and Shape:
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
Lingual AspectLingual Aspect
Lingual AspectLingual Aspect
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
Lingual AspectLingual Aspect
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
Lingual AspectLingual Aspect
4. Mesiolingual Groove:
Frequently seen on Mandibular 1st
premolar only
Proximal Aspect Of Mandibular Proximal 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 Mandibular Proximal 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
Proximal AspectProximal Aspect
3. Height of Contour:
Mandibular 1st premolar
Buccal = cervical 1/3 Lingual = middle
1/3
Proximal AspectProximal Aspect
3. Height of Contour:
Mandibular 2nd premolar
Buccal = junction of cervical
and middle 1/3
Lingual = middle 1/3
Proximal Aspect Proximal Aspect
4. Cervical Lines:
Both premolars have greater curve on the mesial than the distal
Mesial
Distal
Proximal AspectProximal Aspect
5. Root (proximal):
Both premolars generally consist of one root
The mandibular 1st premolar occasionally will have a furcated root
Proximal Aspect Proximal Aspect
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
Proximal Aspect Proximal Aspect
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 Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar
1. Outline:
– Have much variation in
occlusal morphology
– Outline is not symmetrical
(more bulky on the distal)DM
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar
1. Outline:
– Often appears as if the mesial side has been pushed inward (mesiolingual corner)
DM
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar1. 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
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar
1. Outline:
– Crown is somewhat
diamond shaped
converging lingually– Shape of crown is
asymmetrical DM
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar
1. Outline:
– Mesial and distal
marginal ridges may
converge lingually
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar
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
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar
2. Ridges, Fossae, Grooves:
– The transverse ridge
may be crossed by
a shallow central groove
extending from mesial to distal fossa
– This is rare
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar
2. Ridges, Fossae, Grooves:– The grooves of the first premolar are fewer in
number, but may be deeper than those of the
second premolar (just like the maxillary)
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular First PremolarFirst Premolar
2. Ridges, Fossae, Grooves:
– Possess a mesial
and distal fossa– Both are circular,
not triangular– Both possess pits– Distal fossa is usually larger and/or deeper
D
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
1. Outline - Two-cusp version:
– Crown is round or oval
shaped with a square
occlusal table
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
1. Outline - Two-cusp version:
– There is slightly more bulk in the mesial half buccolingually than in the distal half
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
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
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
2. Ridges, Fossae, Grooves - Two-cusp version:
Possess a curved central
groove with no lingual
grooveThis groove can be fairly
straight
D
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
1. Outline - Three-cusp version:
– When lingual cusps are
large, the occlusal
surface is broader on the
lingual
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
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
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
2. Ridges, Fossae, Grooves - Three-cusp version:
Possess three triangular
ridges converging toward
the central fossa
There is no transverse ridge
1
2 3
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
2. Ridges, Fossae, Grooves - Three-cusp version:
Has a central fossa
(unique) shifted
towards the distalLacks a central grooveMesial groove present
M
C
D
Occlusal Aspect Of Mandibular Occlusal Aspect Of Mandibular Second PremolarSecond Premolar
2. Ridges, Fossae, Grooves - Three-cusp version:
Possess a lingual groove that separates the two lingual cusps
This groove completes the Y-shaped occlusal groove pattern