Bicuspid:configuration and function
premolar
premolar
1.maxillary first premolar 4 4
The biggest one of the premolar,the
tip of the facial cusp is located
distally to the midline,
（ 1） crown
1） facial aspect
a,pentagon similar to the
canine;tip of the facial
cusp located distally;distal
ridge short and convex
b.a slight indentation at
mesial ridge;the mesial
contact concave
Crown
c.axial ridge parallel
to long axis;two
developmental grooves
d.crest of contour:the
cervical third of the
crown,cervical ridge
Crown
2） lingual aspect
a.less than buccal
aspect,convex
b.lingual cusp mesially
c.crest of contour,
middle third
Crown
3） proximal surface
a,quadrangle
b.buccal cusp longer and
more pointed than lingual
one
c.mesial marginal groove
and mesial developmental
depression
d.straight axis
Crown
4） occlusal aspect
a,hexagon:shorter and
narrower mesiodistally
b.cusp ridges and marginal
ridges,
c.buccul cusp distally:long and pointed
lingual cusp mesially:short and flat
Crown
d.fossa
e.developmental
groove
Root
flat,bifurcated common
（ 80%）
tip of the root distally
bifurcated:buccal root
larger and longer
single,groove found
Premolar
2.maxillary second premolar 5 5
Resemble the maxillary first
premolars
less angular,more rounded,smaller
（ 1） crown
1） buccal aspect
a.buccal cusp less
pointed,mesially
mesial ridge shorter
b.buccal axial ridge less
pointed;developmental
grooves less prominence
Crown
2） lingual aspect
little variation
cusps almost same
length
crest of
contour:middle third
Crown
3） proximal surface
a.convex
b,cusps almost same length
c.no deep developmental
groove;no deep developmental
depression
Crown
4） occlusal
a.more rounded
ovoid rather than hexagonal
b.4 marginal
ridges:approximately equation
颊缘 =舌缘，近中 =远中
c.two cusps mesially,blunt,
similitude
Crown
d.less distinct fossa
e.groove shorter and
more irregular
Root
Usually single
With a longitudinal
groove
Difference between maxillary first
and second premolar
maxillary, buccolingually longer
straight crown
mandibular,buccolingually and
mesiodistally same
measurement
crown leaning lingually
Difference between maxillary and
mandibular premolar
Premolar
3.mandibular first premolar 4 4
Smallest one of the premolar
Short lingual cusp
Transverse ridge
（ 1） crown
1） buccal aspect
a.lean lingually
buccal cusp mesially
mesial cusp ridge
shorter
b.convex at the cervical
and middle third
c.development groove
Crown
2） lingual aspect
a.taper lingually（ 1/2）
b.mesiolingual developmental
groove
c.slope toward lingual side
Crown
3） proximal surface
a,slope toward lingual
side
b.distinctive buccal
cusp
c.buccal cusp on the axis
Crown
4） occlusal aspect
a.individual variation
b.buccal margin well
developed
c.lingual cusp very small
d.transverse ridge
mesial and distal fossa
e.developmental groove
Crown
（ 2） root
nomally single rooted
flat and slim
longitudinal groove
Premolar
4.mandibular second premolar 5 5
always larger than a mandibular
first premolar
almost the same measurement
occlusocervically,mesiodistally,bucc
olingually
（ 1） crown
1） buccal aspect
lingually sloping not so
much;shorter buccal cusp
than a first one;mesiobuccal
and distobuccal cusp ridges
more rounded;slightly broad
cervical
Crown
2） lingual aspect
a.resemble the buccal
aspect
b.one or two lingual cusp
1舌尖偏近中
2舌尖，近中 >远中舌尖
Crown
3） proximal aspect
slope lingually not so much
buccal cusp at the buccal
side of the axis
Crown
4） occlusal aspect
2cusps 3cusps
shape ellipse squareness
cusp buccal one lingually
linggually mesial>distal
groove H,U-shape Y-shape
（ 2） root
single root:more rounded
longer and wider
buccolingually
Difference between mandibular first
and second premolar
1．如何区分上下颌前磨牙
2．如何区分上颌前磨牙。（近远中）
3．如何区分下颌前磨牙。（近远中）
4．如何区分下颌第一前磨牙及上颌尖牙。
思考题,
1.extraction of teeth:torsion and joggle
2.decayed tooth:self cleaning
3.orthodontics:crowd teeth
4.central cusp:pulpitis and periapical
periodontitis
To dentist
premolar
premolar
1.maxillary first premolar 4 4
The biggest one of the premolar,the
tip of the facial cusp is located
distally to the midline,
（ 1） crown
1） facial aspect
a,pentagon similar to the
canine;tip of the facial
cusp located distally;distal
ridge short and convex
b.a slight indentation at
mesial ridge;the mesial
contact concave
Crown
c.axial ridge parallel
to long axis;two
developmental grooves
d.crest of contour:the
cervical third of the
crown,cervical ridge
Crown
2） lingual aspect
a.less than buccal
aspect,convex
b.lingual cusp mesially
c.crest of contour,
middle third
Crown
3） proximal surface
a,quadrangle
b.buccal cusp longer and
more pointed than lingual
one
c.mesial marginal groove
and mesial developmental
depression
d.straight axis
Crown
4） occlusal aspect
a,hexagon:shorter and
narrower mesiodistally
b.cusp ridges and marginal
ridges,
c.buccul cusp distally:long and pointed
lingual cusp mesially:short and flat
Crown
d.fossa
e.developmental
groove
Root
flat,bifurcated common
（ 80%）
tip of the root distally
bifurcated:buccal root
larger and longer
single,groove found
Premolar
2.maxillary second premolar 5 5
Resemble the maxillary first
premolars
less angular,more rounded,smaller
（ 1） crown
1） buccal aspect
a.buccal cusp less
pointed,mesially
mesial ridge shorter
b.buccal axial ridge less
pointed;developmental
grooves less prominence
Crown
2） lingual aspect
little variation
cusps almost same
length
crest of
contour:middle third
Crown
3） proximal surface
a.convex
b,cusps almost same length
c.no deep developmental
groove;no deep developmental
depression
Crown
4） occlusal
a.more rounded
ovoid rather than hexagonal
b.4 marginal
ridges:approximately equation
颊缘 =舌缘，近中 =远中
c.two cusps mesially,blunt,
similitude
Crown
d.less distinct fossa
e.groove shorter and
more irregular
Root
Usually single
With a longitudinal
groove
Difference between maxillary first
and second premolar
maxillary, buccolingually longer
straight crown
mandibular,buccolingually and
mesiodistally same
measurement
crown leaning lingually
Difference between maxillary and
mandibular premolar
Premolar
3.mandibular first premolar 4 4
Smallest one of the premolar
Short lingual cusp
Transverse ridge
（ 1） crown
1） buccal aspect
a.lean lingually
buccal cusp mesially
mesial cusp ridge
shorter
b.convex at the cervical
and middle third
c.development groove
Crown
2） lingual aspect
a.taper lingually（ 1/2）
b.mesiolingual developmental
groove
c.slope toward lingual side
Crown
3） proximal surface
a,slope toward lingual
side
b.distinctive buccal
cusp
c.buccal cusp on the axis
Crown
4） occlusal aspect
a.individual variation
b.buccal margin well
developed
c.lingual cusp very small
d.transverse ridge
mesial and distal fossa
e.developmental groove
Crown
（ 2） root
nomally single rooted
flat and slim
longitudinal groove
Premolar
4.mandibular second premolar 5 5
always larger than a mandibular
first premolar
almost the same measurement
occlusocervically,mesiodistally,bucc
olingually
（ 1） crown
1） buccal aspect
lingually sloping not so
much;shorter buccal cusp
than a first one;mesiobuccal
and distobuccal cusp ridges
more rounded;slightly broad
cervical
Crown
2） lingual aspect
a.resemble the buccal
aspect
b.one or two lingual cusp
1舌尖偏近中
2舌尖，近中 >远中舌尖
Crown
3） proximal aspect
slope lingually not so much
buccal cusp at the buccal
side of the axis
Crown
4） occlusal aspect
2cusps 3cusps
shape ellipse squareness
cusp buccal one lingually
linggually mesial>distal
groove H,U-shape Y-shape
（ 2） root
single root:more rounded
longer and wider
buccolingually
Difference between mandibular first
and second premolar
1．如何区分上下颌前磨牙
2．如何区分上颌前磨牙。（近远中）
3．如何区分下颌前磨牙。（近远中）
4．如何区分下颌第一前磨牙及上颌尖牙。
思考题,
1.extraction of teeth:torsion and joggle
2.decayed tooth:self cleaning
3.orthodontics:crowd teeth
4.central cusp:pulpitis and periapical
periodontitis
To dentist
