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DENTAL ANATOMY
1st Semester 2008/2009 Academic Year
Department of Stomatology
School of Stomatology
Wenzhou Medical College
Morphology of
Premolars
Kevin Yang
Li Hong-qing
SECTION 1 OVERVIEW
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Objectives
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Describe the functions of premolars
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List class traits common to all premolars
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List arch traits that can be used to distinguish
maxillary from mandibular premolars
A General description of premolars
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What’s premolar ?
Pre- loanword from Latin, where it meant
“before”; applied freely as a prefix, with the
meanings “prior to,” “early,” “beforehand,”
“before,” “in front of,” etc.
 Any tooth in the permanent dentition that
replaces a primary molar.
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Locations and numbers
B Functions of premolars
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Mastication of food
Maintain the vertical dimension of the face
Shearing or cutting food (first premolar)
Support the corners of the mouth and
cheeks
C Class traits of premolars
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Class traits similar to anterior teeth
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Number of development lobes
Tooth name
Cusps
Lobes
Max.1 pre
2
3+1=4
Max.2 pre
2
3+1=4
Mandi.1 pre
2
3+1=4
Mandi.2 pre
2 or 3
4 or 5
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Crowns taper toward the cervical
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Widest proximal heights of contour
Cervical lines
Proximal view
 Buccal or lingual view
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Root shape
Roots taper apically
 Apical third bends distally
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Class traits that differ from anterior teeth
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Tooth surface terminology
posterior
buccal
occlusal surface
cusps\ridges\groo
ves
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anterior
labial
occlusal edge
cingulum
Occlusal cusps versus incisal edges
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1 buccal cusp 1 lingual cusp ( EXCEPTION)
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Marginal ridges
Oriented in a horizontal plane (<45°)
 ( EXCEPTION) (=45°)
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Crown and root length
Crowns: shorter than anterior teeth
 Roots: < canines, >=incisors
 1st premolars vs 2nd premolars: 1st pre crowns
longer but roots shorter
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Height (crest) of contour
Facial height of contour: cervical third
 Lingual height of contour: middle third
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Other class traits characteristic of most
premolars
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Buccal view
Crown outline shape: five-sided pentagon
 Contact areas: distal contacts are more cervical
than mesial contacts (EXCEPTION)
 Cusp ridges size: buccal cusp is slightly mesial
(EXCEPTION)
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Lingual view
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Crown shape: narrower than buccal side
(EXCEPTION)
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Proximal views
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Mesial marginal ridges are more occlusal than
distal marginal ridges
Occlusal view
Tooth proportions: faciallingual dimension wider
than mesiodistal dimension
 Ridges bound occlusal table: cusp ridges and
marginal ridges
 Transverse ridges: triangular ridges (EXCEPTION)
 Grooves and fossae: mesialdistally from mesial
fossa to distal fossa (EXCEPTION)
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D Arch traits that differentiate
maxillary from mandibular
premolars
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Relative shape and size
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The maxillary premolars look more alike than
the mandibular premolars
Lingual crown tilt in mandibular premolars
Tilt lingually relative to the roots
 Fit & function both beneath and lingual to the
maxillary buccal cusps
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Cusp size and location
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Distal crown tilt on mandibular premolars
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Distal tilting from canine to molars
Buccal ridge prominence
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Difference of cusps
Max 1st vs mand 1st
Crown proportions
Max oblong rectangular
 Mand square
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SECTION 2 TYPE TRAITS
DIFFERENTIATE 1st FROM 2nd
MAXILLARY PREMOLARS
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Objectives
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Class traits to distinguish maxillary 1st
premolar from 2st premolar
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Number any maxillary premolar
A type traits from the buccal view
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Relative size of crowns
Crown: 1st >2nd in size
 Root: 1st < 2nd in length
 Shoulders
 Crown taper
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Location of proximal contacts
Mesial: middle third near the junction of the
occlusal and middle thrids
 Distal: more cervical
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Location of the buccal cusp tip
Slightly to the distal for the1st premolar
 Cusp ridges
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Shape of the buccal cusp
1st cusp angle: 100-110° long sharp
 2nd cusp angle: 125-130 ° obtuse
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Buccal ridge and depression
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1st prominent than 2nd
Roots
1st 61% 2 roots
 2nd mostly one root , long , root-to-crown ratio
1.8:1
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B Type traits from the lingual view
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Relative cusp size
shorter and narrower than buccal cusp
 1st premolar more prominent
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Cusp ridges
Meet at a rounded angle
 2nd relatively sharper
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Lingual cusp position
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Tip is to the mesial of the midroot axis line
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Marginal ridges
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Distal ridge more cervical
Roots
1st lingual root shorter than the buccal root
 Root taper to the lingual
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C type traits from the proximal views
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Crown shape and morphology
Trapezoid
 Mesial concavity cervical of 1st
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Relative cusp height
1st buccal longer
 2st equal
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Height of contour
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Buccal or lingual
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Marginal ridge grooves
1st marginal ridge groove: mesial 97% distal
39%
 2nd less
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Cervical lines
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Curvature of mesial & distal
Roots and root depressions
Concavity
 Lingual root shorter
 1st only premolar that mesial depression
deeper than distal
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D type traits from the occlusal view
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Relative size
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1st >= 2nd 82%
Grooves and fossae
1st longer central groove
 2nd more Supplementary grooves
 1st mesial marginal ridge groove
 Distal fossae always >= mesial ones in size
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Relative proportions
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Demention buccolingually > mesiodistally
Outline
Asymmetrical occlusal outline of 1st
 1st Marginal ridge
 2nd symmetrical
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Contact areas &
heights
1st
 2nd
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SECTION 3 TYPE TRAITS
DIFFERENTIATE 1st FROM 2nd
MANDIBULAR PREMOLARS
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Objectives
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Class traits to distinguish mandibular 1st
premolar from 2st premolar
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Number any mandibular premolar
A