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

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

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 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

Mandibular 2nd premolar with 1 lingual cusp:

Lingual cusp is smaller than buccal cusp, but larger than lingual cusp of 1st premolar

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

3. Marginal Ridges:

Mandibular 1st premolar:

Only tooth in the mouth where the mesial marginal ridge is more apical than the distal marginal ridge

3. Marginal Ridges:

Mandibular 2nd premolar:

Mesial marginal ridge is more occlusal than the distal marginal ridge (as found in all other teeth)

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

3. Height of Contour:

Mandibular 1st premolar

Buccal = cervical 1/3 Lingual = middle

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

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 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

1. Outline:

– Often appears as if the mesial side has been pushed inward (mesiolingual corner)

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

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

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)

– Possess a mesial

and distal fossa– Both are circular,

not triangular– Both possess pits– Distal fossa is usually larger and/or deeper

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

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

grooveThis groove can be fairly

straight

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

2. Ridges, Fossae, Grooves - Three-cusp version:

Possess three triangular

ridges converging toward

the central fossa

There is no transverse ridge

Has a central fossa

(unique) shifted

towards the distalLacks a central grooveMesial groove present

Possess a lingual groove that separates the two lingual cusps

This groove completes the Y-shaped occlusal groove pattern

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