Morphology of Premolars Flashcards
Universal Numbering of Maxillary Premolars
R 4, 5
L 12, 13
Universal Numbering of Mandibular Premolars
R 28, 29
L 20, 21
Functions of Premolars
- Mastication
- Maintaining vertical dimension of face
- Assist canines to shear or cut food
- Support cheeks and corners of the mouth
Class Traits of Premolars
• Most premolars have two cusps (one buccal and one
lingual) but sometimes there are three cusps (one
buccal and two lingual); therefore, the term
“premolar” is better than “bicuspid”
• Premolars develop from three facial lobes (like
anterior teeth) and from one or two lingual lobes
corresponding to one or two lingual cusps
Class Traits of Premolars Similar to Anterior
Teeth
Crowns taper to
cervical
Cementoenamel
junction (CEJ) similar in
shape (but less curve)
Roots: taper narrower
apically and lingually
Class Traits of Premolars That Differ From Anterior
Teeth
Two or three occlusal cusps versus incisal edge
Marginal ridges more horizontal (EXCEPT mesial
marginal ridge of mandibular first premolar)
Crowns are shorter
Height of contour: facial in cervical third (not to
close to CEJ, EXCEPT mandibular fist premolar) and
lingual in middle third
Proximal contact areas more cervical and
broader
All Premolars From Buccal View
Pentagon outline of
crown (like canine)
Contact areas are convex; distal contact is more cervical than mesial (EXCEPT mandibular first premolar)
Mesial cusp ridge
shorter than distal
(EXCEPT maxillary first
premolar)
All Premolars From Lingual View
Crown outline narrows toward lingual so some
proximal surfaces are visible (EXCEPT some
three-cusp-type mandibular second premolars with two
lingual cusps [seen best on occlusal view])
Buccal cusp longer than lingual cusp
• Lingual cusp off center to the mesial EXCEPT mandibular first premolar
Which premolar is the exception to the lingual cusp off center to the mesial?
mandibular first premolar
All Premolars From Proximal Views
Mesial marginal ridges are more occlusal than
distal (EXCEPT mandibular first premolar)
Mesial marginal ridges are more occlusal than
distal, except _________
mandibular first premolar)
All Premolars From Occlusal View
Wider faciolingually than mesiodistally
Occlusal table bound by marginal and cusp ridges
Proximal contacts are located buccal to the buccolingual midline; lingual embrasure spaces are larger
Triangular ridges join to form transverse ridges (EXCEPT threecusp-type mandibular second premolars).
A groove extends from mesial fossa to distal fossa (EXCEPT some mandibular first premolars)
Arch Traits That Differentiate Maxillary
From Mandibular Premolars
Mandibular premolars have more noticeable
lingual crown tilt than maxillary
Mandibular have less prominent buccal ridge
Less prominent buccal ridge (mandibular vs maxillary)
Mandibular
All premolars are larger buccolingually than
mesiodistally, true or false?
True
______ premolar is closer to square (buccolingual slightly greater than mesiodistal)
while ______ premolar is rectangular
mandibular = square
maxillary = rectangle
Relative Size of Maxillary Premolar Crowns From the Buccal View
Maxillary first premolar is larger than second
More convergence from proximal contact to cervical on first than second
Location of Contacts for Maxillary Premolars From the Buccal View
Mesial contact junction of occlusal and middle third, distal contact middle third (both types)
Location of Buccal Cusp Tip of Maxillary Premolars From the Buccal View
Maxillary second: mesial cusp ridge is shorter than distal (cusp tip mesial or centered)
Maxillary first premolar has mesial cusp ridge longer than the distal (UNIQUE) (cusp tip distal)
Shape of the Buccal Cusp of Maxillary Premolars From the Buccal View
Cusp is sharper on maxillary first premolar than second
Buccal Ridge and Depression of Maxillary Premolars From the Buccal View
Buccal ridge more prominent on maxillary first premolar than maxillary second
Root of Maxillary Premolars From the Buccal View
Maxillary first premolar is more likely to have two roots, whereas maxillary second premolar has one
When identifying the difference between maxillary premolars from the BUCCAL view, what 6 traits can help you distinguish between the first and second premolar?
- relative size of crown
- location of contacts
- buccal cusp tip location
- shape of buccal cusp
- buccal ridge and depression
- root #
Relative Cusp Size of Maxillary Premolars From the Lingual View
Lingual cusp shorter than buccal cusp; more so on maxillary first premolar than second
Cusp Ridges of Maxillary Premolars From the Lingual View
Lingual cusp is relatively sharper on maxillary second premolar than on first premolar
Lingual Cusp Position for Maxillary Premolars From the Lingual View
Both maxillary first and second premolars have
the lingual cusp tip positioned Mesial to the midroot axis
Marginal Ridges of Maxillary Premolars From the Lingual View
Distal marginal ridge is more cervical than
mesial for both maxillary first and second premolars (best seen by comparing mesial and distal views)
Roots of Maxillary Premolars From the Lingual View
Maxillary first premolar: lingual root is shorter than buccal root
Root crown ratio is 1.56 on first premolar and 1.82 on second premolar
Crown Shape and Morphology of Maxillary Premolars From the Proximal Views
Maxillary premolars have trapezoid outline
Maxillary first premolar is the only premolar to have a crown depression (always on
the mesial)
Relative Cusp Height of Maxillary Premolars From the Proximal Views
Lingual cusp shorter than buccal cusp, more so on maxillary first premolar than second premolar
Height (Crest) of Contour of Maxillary Premolars From the Proximal Views
Facial height of contour is in cervical third (like all teeth)
Lingual height of contour is in the middle third (like all posterior teeth)
Distance Between Cusps on Maxillary Premolars From the Proximal Views
Distance between cusps is same for maxillary first and second premolars
Both buccal and lingual cusp tips are located over the root
Marginal Ridge Grooves of Maxillary Premolars From the Proximal Views
Marginal ridge groove is found most often on the mesial marginal ridge of maxillary first premolar
Not as common on all other maxillary premolar
Cervical Lines of Maxillary Premolars When Comparing the Proximal Views
More CEJ curvature on mesial than distal on both first and second premolars (as on all premolars and anterior
teeth)
Roots and Root Depressions of Maxillary Premolars From the Proximal Views
Maxillary first premolar is only premolar with the mesial root depression more pronounced than
distal; only premolar with a mesial crown depression joining with the deep root depression
Distal root depression more pronounced on maxillary second premolar
Relative Size of Maxillary Premolars From the Occlusal View
Maxillary first premolar likely to be slightly larger than second
Grooves and Fossae of Maxillary Premolars From the Occlusal View
Central groove of maxillary first premolar is longer than on second premolar
Maxillary second premolar has more supplemental grooves than first
Relative Proportions of Maxillary Premolars From the Occlusal View
Both maxillary premolars have noticeably greater dimension faciolingually than mesiodistally (by over 2 mm)
Outline of Maxillary Premolars From the Occlusal View
Buccal ridge more prominent on maxillary first premolar than second
Maxillary first premolar outline is more asymmetrical (hexagonal) than second premolar
Contact Areas and Heights of Contour of Maxillary Premolars From the Occlusal View
Contacts are near junction of buccal/middle thirds for both
Type Traits That Differentiate Mandibular First From Mandibular Second Premolars
• Mandibular premolars vary in shape more than
maxillary premolars
• Mandibular second premolar is the only
premolar more likely to have three cusps (one
buccal and two lingual: mesiolingual and distolingual)
Which premolar is the only premolar likely to have three cusps?
Mandibular second premolar (one
buccal and two lingual: mesiolingual and distolingual)
Relative Crown Shape and Size of
Mandibular Premolars From the Buccal View
- Mandibular first premolar is longer than the second
- Both have rounded shoulders (first wider than second)
- Buccal cusp apex of mandibular first premolar is sharper than second
- Cusp ridge notches more common on mesial of first and distal of second
Morphology of Mandibular Premolars
From the Buccal View
•Buccal developmental grooves on either side of buccal ridge (when present) are likely
deeper on the mesial of first premolar and
on the distal of second premolar
• Mesial cusp ridges shorter than distal
Cervical Lines of Mandibular
Premolars From the Buccal View
CEJ is more curved on mandibular first
premolar than second
Contact Areas of Mandibular
Premolars From the Buccal View
• Mandibular first premolar is the only
premolar (only adult tooth) where the mesial contact is more cervical than the distal
• First premolar distal contact is in occlusal third and mesial is at junction of occlusal and middle or middle
_____ is the only adult tooth where the mesial contact is more cervical than the distal
Mandibular first premolar
Roots of Mandibular Premolars From the
Buccal View
- Both types of mandibular premolar roots taper to apex with distal bend of apex more common
- Root crown ratio on second premolar is larger
Crown Shape of Mandibular Premolars
From the Lingual View
Most mandibular premolars taper narrower toward lingual (EXCEPT three-cusp type of mandibular second premolar where lingual half may be wider than buccal half)
Which mandibular premolar(s) may have a wider lingual half than the buccal half from the lingual view?
a. mandibular first premolar
b. mandibular second premolar
c. mandibular second premolar, 3 cusp type
d. a and b
e. all of the above
c. mandibular second premolar, 3 cusp type
Lingual Cusps of Mandibular
Premolars From the Lingual View
Lingual cusp of mandibular first premolar is quite a bit shorter than the buccal; is non functional and is located just mesially of center
Lingual cusp of mandibular second premolar (with one lingual cusp) is slightly shorter than the buccal, and is mesial to midroot axis
When the mandibular second premolar has two lingual cusps, the mesiolingual cusp is normally wider and longer than the distolingual
Lingual cusp of mandibular second premolar (with one lingual cusp) is slightly \_\_\_\_ than the buccal, and is \_\_\_\_\_ to midroot axis
lingual slightly shorter than buccal
and mesial to midroot axis
When the mandibular second premolar has
two lingual cusps, the mesiolingual cusp is
normally _______ than the
distolingual
wider and longer
The \_\_\_\_\_\_ is the only premolar (only posterior tooth) to have its mesial marginal ridge more cervical than the distal
mandibular first premolar
Grooves on Mandibular Premolars From
the Lingual View
Only mandibular second premolars with two lingual cusps have a lingual groove separating them
Most mandibular first premolars have a
mesiolingual groove separating mesial marginal ridge from the mesial cusp ridge of the lingual cusp
Only mandibular ______ with two lingual cusps have a lingual groove separating them
second premolars
Most mandibular first premolars have a
________ separating mesial marginal ridge from the mesial cusp ridge of the lingual cusp
mesiolingual groove
Roots of Mandibular Premolars From the
Lingual View
Roots taper lingual to apex
Crown Shape of Mandibular Premolars
From the Proximal Views
• Crowns tip noticeably to the lingual, more so onbmandibular first premolar
than second
• Outlines are rhomboid
• Lingual cusps are shorter than buccal, more so on first with nonfunctional lingual cusp
Marginal Ridges of Mandibular
Premolars From the Proximal Views
- Mesial marginal ridge of mandibular first premolar slopes at 45º, nearly parallel to buccal triangular ridge
- Lingual triangular ridge is very short
- Other posterior marginal ridges are more horizontal
- Occlusal plane in relation to midroot axis line 45º on first.
Marginal Ridge Grooves and Mesiolingual
Grooves on Mandibular Premolars From the Proximal Views
• Mesiolingual groove is often present on
mandibular first premolars, not seconds
• Second premolars sometimes have
marginal ridge grooves
Mesiolingual groove is often present on
mandibular ____ premolars, not ____
first premolars, NOT seconds
Height (Crest) of Contour of Mandibular Premolars From the Proximal Views
• Buccal height of contour is in cervical third (near CEJ on first premolar)
• Lingual height is in middle third, nearly to cusp tip in mandibular first premolar,
and beyond root outline
Cervical Lines of Mandibular
Premolars From the Proximal Views
• More CEJ curve on mesial than distal
surface (as on all premolars)
• Lingual CEJ is more occlusal than buccal (as on all premolars)
Roots of Mandibular Premolars From the
Proximal Views
taper to apex (as all do)
Root Depressions of Mandibular
Premolars From the Proximal Views
• Mandibular first premolar has mesial
and distal root depressions, deeper on
distal
• Mandibular second premolar likely to have distal root depression, but none on mesial
Outline Shape of Mandibular
First Premolars From the Occlusal View
– Has more bulk in distal half than mesial half
– Mesiolingual line angle is flat (pushed in)
– Diamond-shaped occlusal outline
– Occlusal table is triangular
Shape of occlusal outline of mandibular first premolar (occlusal view)
Diamond
Shape of occlusal table of mandibular first premolar (occlusal view)
Triangle
Outline Shape of Mandibular
Second Premolars From the Occlusal View
– Two-cusped type has almost rounded outline
– Three-cusped type has more square outline; may actually taper narrower from lingual to buccal
– Occlusal tables are square
Shape of occlusal table of mandibular second premolar (occlusal view)
Square
Ridges, Fossae, and Grooves of Mandibular First Premolars From the Occlusal View
• Prominent transverse ridge may separate mesial and distal fossae (with no central groove) • Mesial and distal circular fossae resemble “snake eyes” • Distal fossa larger than mesial • Mesiolingual groove extends from mesial circular fossa
Occlusal Fillings (“Snake Eyes”) on \_\_\_\_\_\_ No Fissured Central Groove, Pronounced Transverse Ridge
mandibular first molar
Ridges, Fossae, and Grooves of the Two-Cusp Mandibular Second Premolars From the Occlusal View
Central groove connects mesial and distal fossae
• Groove pattern may be H or U shaped
• Buccal and lingual triangular ridges form
transverse ridge.
Ridges, Fossae, and Grooves of the Three-Cusp Mandibular Second Premolar
- Three triangular ridges; none connect so there is no transverse ridge
- Only premolar with central fossa
- Central groove may be called mesial and distal grooves joining at central fossae
- Lingual groove forms “Y” pattern
Marginal Ridge Grooves of Mandibular
Premolars From the Occlusal View
Marginal ridge grooves are not common on
mandibular premolars (although the mandibular first premolar often has a mesiolingual groove, which
separates the mesial marginal ridge from mesial cusp ridge of lingual cusp)
