Human dentition Dr. Hazem Al Ajrami First Year in Dentistry First Semester Al-Azhar University - Gaza lecture 12

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College of DentistryCollege of Dentistry
Human Dentition IHuman Dentition I
Mandibular Second PremolarMandibular Second Premolar
Dr. Hazem Al AjramiDr. Hazem Al Ajrami

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Universal Numbering System:Universal Numbering System:
20 and 2920 and 29
Palmer Notation System:Palmer Notation System:
FDI Numbering System:FDI Numbering System:
35 and 4535 and 45
55 andand 55

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Chronology:Chronology:
A.A. First evidence of calcification:First evidence of calcification: 2 ¼2 ¼ toto 2 ½2 ½
years.years.
B.B. Enamel completed:Enamel completed: 66 toto 77 years.years.
C.C. Eruption:Eruption: 1111--1212 years.years.
D.D. Root completed:Root completed: 1313--1515 years.years.

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Cervico-Cervico-
OcclusalOcclusal
LengthLength
ofof
CrownCrown
LengthLength
ofof
RootRoot
MesiodistalMesiodistal
DiameterDiameter
of Crownof Crown
MesiodistalMesiodistal
DiameterDiameter
of Crownof Crown
at Cervixat Cervix
MandibularMandibular
SecondSecond
PremolarPremolar
88 14.514.5 77 55

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Bucco-Bucco-
linguallingual
DiameteDiamete
r ofr of
CrownCrown
Bucco-Bucco-
linguallingual
DiameterDiameter
of Crownof Crown
at Cervixat Cervix
CurvatureCurvature
ofof
CervicalCervical
LineLine
(Mesial)(Mesial)
CurvatureCurvature
ofof
CervicalCervical
LineLine
(Distal)(Distal)
MandibulaMandibula
r Secondr Second
PremolarPremolar 88 77 11 00

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The mandibular second premolar is alwaysThe mandibular second premolar is always
larger than the mandibular first premolar. Itslarger than the mandibular first premolar. Its
lingual cusp are more developed, and bothlingual cusp are more developed, and both
marginal ridge are higher. This producers amarginal ridge are higher. This producers a
more efficient occlusion with the maxillarymore efficient occlusion with the maxillary
antagonist. Therefore a mandibular secondantagonist. Therefore a mandibular second
premolar functions more like molar than apremolar functions more like molar than a
canine.canine.

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There are two common forms which thisThere are two common forms which this
tooth assumes:tooth assumes:
1.1. The three cusp type (tricuspid): which is theThe three cusp type (tricuspid): which is the
most common and appears more angularmost common and appears more angular
from the occlusal aspect.from the occlusal aspect.
It has one larger buccal cusp (composed of 3It has one larger buccal cusp (composed of 3
buccal lobes) and two smaller lingual cuspsbuccal lobes) and two smaller lingual cusps
(composed of 2 lingual lobes).(composed of 2 lingual lobes).

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2.2. The two-cusp type (bicuspid): appear moreThe two-cusp type (bicuspid): appear more
rounded from the occlusal aspect. It is lessrounded from the occlusal aspect. It is less
common and has a large buccal cusp and acommon and has a large buccal cusp and a
single smaller lingual cusp.single smaller lingual cusp.
The single root of the second premolar isThe single root of the second premolar is
larger than that of the first premolar.larger than that of the first premolar.

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Buccal AspectBuccal Aspect
From the buccal aspect the crown resembles aFrom the buccal aspect the crown resembles a
first premolar in its general shape and in factfirst premolar in its general shape and in fact
the contact areas, mesially and distally, arethe contact areas, mesially and distally, are
near the same level. However, the contactnear the same level. However, the contact
areas are broad and higher (just cervical to theareas are broad and higher (just cervical to the
junction of the occlusal and middle thirds).junction of the occlusal and middle thirds).

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Distal Mesial

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It presents shorter buccal cusp than the firstIt presents shorter buccal cusp than the first
premolar with the mesiobuccal and distobuccalpremolar with the mesiobuccal and distobuccal
cusp ridges more rounded.cusp ridges more rounded.
The root is longer and broader mesiodistallyThe root is longer and broader mesiodistally
than the first premolar and ends in more bluntthan the first premolar and ends in more blunt
apex.apex.
The crown bears some resemblance from thisThe crown bears some resemblance from this
aspect to the mandibular first premolar butaspect to the mandibular first premolar but
there are some differences:there are some differences:

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1.1. The crown is slightly larger, but the buccalThe crown is slightly larger, but the buccal
cusp is shorter and less pointed.cusp is shorter and less pointed.
2.2. The buccal cusp slopes are less steep andThe buccal cusp slopes are less steep and
nearly equal to each other.nearly equal to each other.
3.3. The crown has wider measurements in theThe crown has wider measurements in the
cervical third.cervical third.

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Mandibular Second Premolar Mandibular First Premolar

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Lingual AspectLingual Aspect
The lingual lobes are developed a greaterThe lingual lobes are developed a greater
degree making the cusp or cusps longer, so thedegree making the cusp or cusps longer, so the
lingual surface is wider mesiodistally andlingual surface is wider mesiodistally and
longer occlusocervically.longer occlusocervically.
The lingual cusp or cusps are higher so less ofThe lingual cusp or cusps are higher so less of
the occlusal surface can be seen from thisthe occlusal surface can be seen from this
aspect when compared to the first premolar.aspect when compared to the first premolar.
The three cusps type presents a mesiolingualThe three cusps type presents a mesiolingual
and distolingual cusps which is separated byand distolingual cusps which is separated by
lingual groove. The mesiolingual cusp is widerlingual groove. The mesiolingual cusp is wider
and longer than the distolingual cusps.and longer than the distolingual cusps.

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Mandibular First PremolarMandibular Second Premolar

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In the two cusp type, the single lingual cusp isIn the two cusp type, the single lingual cusp is
higher than on a mandibular first premolar. Nohigher than on a mandibular first premolar. No
lingual developmental groove is present, but alingual developmental groove is present, but a
developmental depression is seen distolinguallydevelopmental depression is seen distolingually
where the lingual cusp ridge joins the distalwhere the lingual cusp ridge joins the distal
marginal ridge.marginal ridge.
The lingual surface of the crown of all mandibularThe lingual surface of the crown of all mandibular
second premolar is smooth and spheroid, having asecond premolar is smooth and spheroid, having a
bulbous form above the constricted cervicalbulbous form above the constricted cervical
portion.portion.
The root is much wider lingually than that of theThe root is much wider lingually than that of the
first premolar. This results in less convergencefirst premolar. This results in less convergence
towards lingual. It is smooth and convex.towards lingual. It is smooth and convex.

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Mesial AspectMesial Aspect
The second premolar differs from the firstThe second premolar differs from the first
premolar from the mesial aspect in thepremolar from the mesial aspect in the
following ways:following ways:
 The crown and root are wider buccolinguallyThe crown and root are wider buccolingually
than the first premolar.than the first premolar.
 The buccal cusp is shorter and its tip locatedThe buccal cusp is shorter and its tip located
more to the buccal side than the first premolar.more to the buccal side than the first premolar.
So the buccal cusp tip is not located over theSo the buccal cusp tip is not located over the
root axis but it is slightly buccal center.root axis but it is slightly buccal center.

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Mandibular Second Premolar Mandibular First Premolar

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 The lingual lobe or lobes development isThe lingual lobe or lobes development is
greater.greater.
 The lingual cusp (cusps) is much moreThe lingual cusp (cusps) is much more
prominent but still shorter than the buccal cuspprominent but still shorter than the buccal cusp
(by 1(by 1 mm.).mm.).
 The marginal ridge is at right angle to the longThe marginal ridge is at right angle to the long
axis of the tooth, and not slopping like the firstaxis of the tooth, and not slopping like the first
premolar.premolar.
 Less of the occlusal surface may be seen.Less of the occlusal surface may be seen.

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 The height of contour of lingual outline isThe height of contour of lingual outline is
located at the occlusal third.located at the occlusal third.
 There is no mesio-lingual developmentalThere is no mesio-lingual developmental
groove on the crown portion.groove on the crown portion.
 The root is longer, wider and in most casesThe root is longer, wider and in most cases
slightly convex on the mesial surface with aslightly convex on the mesial surface with a
more blunt apex.more blunt apex.

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Distal AspectDistal Aspect
Like the mesial aspect but in the three cuspLike the mesial aspect but in the three cusp
type the distolingual cusp is shorter than thetype the distolingual cusp is shorter than the
mesiolingual cusp.mesiolingual cusp.
More of the occlusal surface can be seenMore of the occlusal surface can be seen
because the distal marginal ridge is at a lowerbecause the distal marginal ridge is at a lower
level than the mesial marginal ridge.level than the mesial marginal ridge.

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Mandibular First PremolarMandibular Second Premolar

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As a general rule, the crowns of all posteriorAs a general rule, the crowns of all posterior
teeth (maxillary and mandubular) are tippedteeth (maxillary and mandubular) are tipped
distally to the long axis of the root. So, muchdistally to the long axis of the root. So, much
of the occlusal surface may be seen from theof the occlusal surface may be seen from the
distal aspect. Another general rule is that thedistal aspect. Another general rule is that the
apex of the root curves distally.apex of the root curves distally.
The angulation’s of occlusal surfaces to longThe angulation’s of occlusal surfaces to long
axes of all posterior teeth is an importantaxes of all posterior teeth is an important
observation to remember, not only in the studyobservation to remember, not only in the study
of individual tooth forms but also later, in theof individual tooth forms but also later, in the
study of alignment and occlusion.study of alignment and occlusion.

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OcclusalOcclusal AspectAspect
In both the two and three-cusp forms, theIn both the two and three-cusp forms, the
buccal cusp is similar; however the outline ofbuccal cusp is similar; however the outline of
each type shows some variations from theeach type shows some variations from the
occlusal aspect.occlusal aspect.
The occlusal characteristics of the three cuspThe occlusal characteristics of the three cusp
type:type:
 The occlusal outline is roughly square. It hasThe occlusal outline is roughly square. It has
three distinct cusps; the buccal cusp is thethree distinct cusps; the buccal cusp is the
largest then the mesiolingual cusp. Thelargest then the mesiolingual cusp. The
distolingual cusp is the smallest.distolingual cusp is the smallest.

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Mesial Distal

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 Each cusp has a well defined triangularEach cusp has a well defined triangular
ridges separated by deep developmentalridges separated by deep developmental
grooves. These grooves converge in a centralgrooves. These grooves converge in a central
in a central pit and form a "Y" shape on thein a central pit and form a "Y" shape on the
occlusal surface.occlusal surface.
 The cusps are separated by twoThe cusps are separated by two
developmental grooves:developmental grooves:
1.1. The V shaped central groove separating theThe V shaped central groove separating the
buccal from the lingual cusps.buccal from the lingual cusps.
2.2. The lingual groove is straight and extendsThe lingual groove is straight and extends
lingually between the lingual cusps.lingually between the lingual cusps.

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 These 2 grooves together form a distinctive YThese 2 grooves together form a distinctive Y
shapes groove on the occlusal surface.shapes groove on the occlusal surface.
 There is central pit, which is located at theThere is central pit, which is located at the
junction of the central and lingual groove. Thejunction of the central and lingual groove. The
mesial and distal triangular fossae are so small.mesial and distal triangular fossae are so small.
 Three pits may be present, a central, a mesial,Three pits may be present, a central, a mesial,
and a distal. There is no transverse ridge butand a distal. There is no transverse ridge but
the triangular ridges of the three cusps meet atthe triangular ridges of the three cusps meet at
the center of the occlusal surface.the center of the occlusal surface.
 The central pit is located in the centerThe central pit is located in the center
buccolingually and slightly distal to thebuccolingually and slightly distal to the
midway point between the mesial and distalmidway point between the mesial and distal
marginal ridges.marginal ridges.

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 From the central pit, a mesial and distalFrom the central pit, a mesial and distal
developmental grooves travel in a mesiobuccaldevelopmental grooves travel in a mesiobuccal
and distobuccal directions respectively ending inand distobuccal directions respectively ending in
the mesial and distal triangular fossae.the mesial and distal triangular fossae.
 The lingual developmental groove extendsThe lingual developmental groove extends
lingually between the two lingual cusps and endslingually between the two lingual cusps and ends
on the lingual surface of the crown just below theon the lingual surface of the crown just below the
lingual cusps and ends on the lingual surface oflingual cusps and ends on the lingual surface of
the crown just below the convergence of thethe crown just below the convergence of the
lingual cusp ridges. The mesiolingual cusp islingual cusp ridges. The mesiolingual cusp is
wider mesiodistally than the distolingual cusp.wider mesiodistally than the distolingual cusp.
 Supplemental grooves and depressions are oftenSupplemental grooves and depressions are often
seen radiating from the developmental groove.seen radiating from the developmental groove.

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The occlusal characteristics of the two-cuspThe occlusal characteristics of the two-cusp
type as compared with the three-cusp type are:type as compared with the three-cusp type are:
The occlusal outline appears rounded. TheThe occlusal outline appears rounded. The
lingual surface is slightly narrower than thelingual surface is slightly narrower than the
buccal.buccal.
The lingual cusp is smaller than the buccalThe lingual cusp is smaller than the buccal
cusp, so there is a large triangular ridge on thecusp, so there is a large triangular ridge on the
buccal cusp and a smaller one on the lingualbuccal cusp and a smaller one on the lingual
cusp. The two ridges form a transverse ridge.cusp. The two ridges form a transverse ridge.
The lingual surface of the crown is moreThe lingual surface of the crown is more
convex and tapers toward the lingual side.convex and tapers toward the lingual side.

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The mesiolingual and distolingual line anglesThe mesiolingual and distolingual line angles
are rounded.are rounded.
There is only well-developed lingual cuspThere is only well-developed lingual cusp
located directly opposite to the buccal cusp inlocated directly opposite to the buccal cusp in
a lingual direction.a lingual direction.
There is no lingual developmental groove.There is no lingual developmental groove.
There is often a curved central developmentalThere is often a curved central developmental
groove which extends mesiodistally across thegroove which extends mesiodistally across the
transverse ridge. It forms U shape groovetransverse ridge. It forms U shape groove
pattern on the occlusal surface. Sometimes thepattern on the occlusal surface. Sometimes the
central groove is short and more straightcentral groove is short and more straight
forming H shape groove pattern.forming H shape groove pattern.

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The central groove of the two-cusp formThe central groove of the two-cusp form
terminates in mesial and distal fossae. Ifterminates in mesial and distal fossae. If
supplemental grooves radiate form thesesupplemental grooves radiate form these
fossae, the "H" groove pattern is present.fossae, the "H" groove pattern is present.
There is usually no central pit, sometimesThere is usually no central pit, sometimes
mesial pit and distal pit are centered in themesial pit and distal pit are centered in the
mesial and distal fossae.mesial and distal fossae.

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Thank YouThank You