Premolars
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Transcript of 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)
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)
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
• 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)
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 root depression is deeper than the mesial depression ( opposite in maxillary 1st premolar; depression on the mesial surface of the root)
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
Chronology
• Initial calcification: 1 ¾ - 2 Years
• Crown completion: 5 – 6 Years
• Eruption: 10 – 12 Years
• Root completion: 12 – 13 Years
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
Chronology
• Initial calcification : 2 ¼ - 2 ½ years
• Completion of crown : 6-7 yrs
• Eruption : 11-12 years
• Completion of root: 13-14 yrs
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
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