Premolars

General Characteristics & Functions:

• 2 premolars per quadrant

• At least 2 cusps, buccal cusp always larger

• Distal to the canines

• Succedaneous

• Shorter crown than anterior teeth

General Characteristics & Functions:

• ‘Transitional tooth’ during chewing, or mastication

• It has properties of both the anterior canines and posterior molars

• Assist molars in grinding, and canines in tearing

• Food can be transferred from the canines --premolars -- molars for grinding

• Support facial muscles (aesthetics and speech)

Permanent Maxillary First Premolars

General morphology

• From buccal aspect, crown resembles maxillary canine • except that mesial slope is longer than distal slope

• Distinct depression on mesial surface, extending from cervical half of crown to root bifurcation

• mesial developmental depression / fossa canina / canine fossa

• *assumed to be caused by pressure from earlier completed crown of maxillary first canine

• The only premolar with two roots• *maxillary second premolars may also have double roots

• Buccal cusp larger than palatal cusp

• From occlusal aspect, buccal side wider than palatal side

• Two cusps separated by deep central groove

Principal identifying features

• Two roots, buccal and palatal (tend to curve distally)

• Two pulp horns and two pulp canals

• Two sharply defined cusps (buccal larger than palatal)

• Mesial developmental depression

• Mesial slope of buccal cusp longer than distal slope

• Palatal cusp tilts slightly mesially

• Occlusal outline more angular than maxillary second premolar

Buccal view features

• Widest mesiodistally (of all premolars)

• Mesial and distal contact – cervical to junction of occlusal and middle third

• Mesial outline more rounded

• Imbrication lines and perikymata

• Mesial slope of buccal cusp is longer than distal slope (helps to distinguish right from left)

Lingual view features• Lingual surface is rounded in all

directions and smaller than buccal surface

• Lingual cusp offset towards mesial

• Mesial cusp slope of lingual cusp is shorter than distal cusp slope

Proximal view features• Mesial developmental depression

extending to the root

• CEJ curvature deeper and more occlusal on the mesial surface compared to distal surface

• Distal surface is similar to mesial (except it does not have a depression)

• More of occlusal surface shows because distal marginal ridge is more cervical than mesial marginal ridge

Occlusal view features• Outline resembles a hexagon

• Wider buccolingually than mesiodistally

• Buccal ridge is prominent on buccal margin

• Lingual margin of occlusal outline is almost a semicircle

• Lingual part narrower mesiodistally than buccal part

Occlusal table components• Four buccal cusp ridges descend from the

buccal cusp tip (buccal, lingual, mesial and distal)

• Four buccal-inclined cuspal planes (mesiobuccal, mesiolingual, distobuccal and distolingual)

• Four lingual cusp ridges

• Four lingual-inclined cuspal planes

Occlusal table components• Transverse ridge (buccal + lingual triangular ridge)

• Long central groove extending mesiodistally (dividing tooth buccolingually)

• Marginal grooves (mesial and distal )

• Triangular grooves (mesiobuccal, distobuccal, mesiolingual and distolingual)

• Two triangular fossa (mesial and distal)

Permanent Maxillary Second Premolars

Chronology

Initial calcification : 2-2.5 years

Completion of crown : 6-7 years

Eruption : 10-12 years

Completion of root : 12-14 years

Maxillary 2nd Premolar (15 & 25)• 5th Tooth from midline of maxilla.

• Maxillary 1st& 2nd premolar resemble each other closely.

• Therefore comparisons are made in relation to maxillary 1st Premolar to be able to distinguish the features between the two.

Description

• Less angular, more rounded crown

• Single root flattened mesiodistally

• Smaller crown cervico-oclusally and mesiodistally, (it also may be larger in those dimensions

• Root length slightly greater than maxillary 1st premolar

• No canine fossa

Buccal aspect

Buccal Aspect

• Shorter cusp, lest pointed

• Mesial slope of buccal cusp ridge is usually shorter than the distal slope (opposite for 1st

premolar)

• Crown and root are thicker at the cervical portion (not a rule)

Lingual aspect

Lingual Aspect

• Lingual cusp is longer

• Therefore crown is longer on lingual side

Mesial aspect

Mesial Aspect

• Shorter Cusp , with the buccal and lingual cusp more nearly the same length

• Greater distance between the cusp tips widens the occlusal surface buccolingually

• Shallow developmental groove on the single tapered root (not found on the Maxillary 1st

premolar)

• No developmental groove crossing the mesial marginal ridge is evident.

Distal aspect

Distal Aspect

• Distal root depression is deeper than the mesial depression ( opposite in maxillary 1st premolar; depression on the mesial surface of the root)

Occlusal aspect

Occlusal Aspect

• Outline of crown is more rounded/oval rather than angular

• Central developmental groove is shorter and more irregular; tendency toward multiple supplementary grooves radiating from the central groove

• Supplementary grooves terminate in shallow depressions in the enamel that may extend to the cusp ridges.

• Irregular and wrinkled occlusal surface

Permanent Mandibular First Premolar

Chronology

• Initial calcification: 1 ¾ - 2 Years

• Crown completion: 5 – 6 Years

• Eruption: 10 – 12 Years

• Root completion: 12 – 13 Years

Tooth Identification

Universal Numbering System

Palmer Notation Method

Tooth Identification

International/FDI system

Buccal Aspect

• A large pointed buccal cusp is seen

• Mesiobuccal cusp ridge is shorter than the distobuccal cusp ridge (similar to that of a canine)

• Concavity is seen occasionally at the mesial and distal slope of the buccal cusp

Lingual Aspect

• Crown tapers lingually

• Lingual cusp is non functional as it is small and pointed

• Some lingual cusp is even shorter than the cingulum of the maxillary canine

• Mesiolingual developmental groove is seen between the mesiobuccal and lingual lobe

Mesial Aspect

• Lingual cusp is around two third the size of the buccal cusp

• Extreme lingual slope is seen at the mesial marginal ridge

• Between the mesial marginal ridge and the mesiolingual cusp ridge is the mesiolingual developmental groove

• Mesial contact area is in the middle third

Distal Aspect

• Distal marginal ridge is higher compared to the mesial marginal ridge and does not have extreme lingual slope

• The cervical line curvature is less curved

Occlusal Aspect

• Two depressions

(mesial and distal fossae) seen on the occlusal surface

• Mesiolingual depression and mesiolingual developmental groove commonly seen

• Lingual cusp tip is shifted mesially

Root

• Single root

• On the mesial aspect of the root, a deep developmental groove is seen

• On the distal aspect, a shallow depression without any developmental groove is present

Permanent Mandibular Second Premolar

Chronology

• Initial calcification : 2 ¼ - 2 ½ years

• Completion of crown : 6-7 yrs

• Eruption : 11-12 years

• Completion of root: 13-14 yrs

Buccal side

R

-Resembles 1st

premolar

-Larger crown

-Shorter and less

pointed buccal cusps

-Broader

Lingual Side

R-Lingual cusp is smaller than

buccal cusp but it is larger than

mandibular first premolar

lingual cusp

-Occlusal surface of buccal

cusp can be seen

Mesial Side

• Dimension at cervical 3rd > occlusal 2rd

• Mesio-lingual cusp is longer and sharper than the mesiobuccal cusp

R

Distal Side

- Crown is narrower

distally than mesially

- Cervical line curves

occlusally

R

Variation

• May have 2 cusps

• Root may be partially bifurcated (Rare)

View Maxillary 1st Premolar Maxillary 2nd Premolar

Occlusal Larger Smaller

Edgy crown More rounded crown

Buccal cusp longer than lingual Two cusps same length

Long central groove Short central grooveMore supplement grooves

Groove interrupts mesial marginal ridge

Mesial marginal ridge not interrupted

Mesial/distal

Shorter root Longer root

Bifurcation with root trunk Single-rooted

Mesial developmental depression (canine fossa)

Convex mesial surface

Buccal Mesial slope longer Distal slope longer

Traits Mandibular first premolar Mandibular second premolar

Buccal cusp and buccal cusp ridge

More prominent and longer Less prominent and shorter buccal cusp

Lingual cusp One, nonfunctional-very small

Usually 2 and functional-longer

Lingual convergence Present, mesiolingual appears to be pushed in

Little taper

Lingual groove Mesiolingual groove present Lingual groove between the 2 lingual cusps

Marginal ridge Mesial marginal ridge lower and parallel to the buccal triangular ridge

Distal marginal ridge lower and mesial, and distal ridges are more horizontal

Lingual crown tilt Severe lingual crown tilt less

Crown outline Diamond shaped Square / Round

Central groove and transverse ridge

Definite transverse ridge and central groove unlikely

3 cusp type has no transverse ridge and ‘Y’ groove pattern

Mandibular 1st vs 2nd premolar

Maxillary vs Mandibular

Traits Maxillary Mandibular

Buccal ridge More prominent Less prominent

Buccal and lingual cusp height difference

Not very prominent More difference

Lingual tilt of crown Crown aligned over the root

Crown tilts lingual relative to the root

Crown width Wider bucco lingually

Less oblong buccolingually

Crown shape Oval or rectangular Square or round