Introduction to Dentistry 9
J. Naim-Faculty of
Dentistry-University of
Palestine
Dr Jamal Naim Naim
PhD Orthodontics
J. Naim-Faculty of
Dentistry-University of
Palestine
J. Naim-Faculty of
Dentistry-University of
Palestine
Numbering of the premolars
The premolars are eight in number, two each Quadrant,
first and second premolar.
J. Naim-Faculty of
Dentistry-University of
Palestine
General
• They comprise with the molars the group of posterior
teeth and supplement them in function.
• The term bicuspid is inaccurate
• They are the last succedaneous teeth and have another
name than their predecessors.
• The general features of the premolars let them
intermediate between canines and molars in function
and form.
J. Naim-Faculty of
Dentistry-University of
Palestine
General
Function:
• The have a tearing cusp tip like canines
• They have an occlusal surface, for grinding, like ,molars.
• The contribute less to esthetics and phonetics than
anterior but more than molars.
J. Naim-Faculty of
Dentistry-University of
Palestine
General
Form:
• Cusp tip like canines and occlusal surface like molars
• The lingual cusps range from none to two cusps.
• Marginal ridges are in a horizontal plane.
• Buccal surface is canine like.
J. Naim-Faculty of
Dentistry-University of
Palestine
General features
• The maxillary premolars are more like
than the mandibular premolars.
• The first upper PM is a little larger than
the second.
• The crown is buccolingually wider than
mesiodistally.
J. Naim-Faculty of
Dentistry-University of
Palestine
General features
• They have nearly equal sized buccal and
lingual cusp.
• The crowns are centered on the root
without lingual inclination.
• The upper first premolar exhibits
normally two root branches.
J. Naim-Faculty of
Dentistry-University of
Palestine
J. Naim-Faculty of
Dentistry-University of
Palestine
Numbering and notation
Tooth
Upper first right premolar
Upper first left premolar
FDI Universal
14
24
#5
#12
Palmer
4
┘
4
└
J. Naim-Faculty of
Dentistry-University of
Palestine
Chronology & Measurements
J. Naim-Faculty of
Dentistry-University of
Palestine
General
• Fourth in position from the midline
• Replaces the first deciduous molar.
J. Naim-Faculty of
Dentistry-University of
Palestine
General
• The occlusal outline is hexagonal.
• Exhibits two nearly equal cusps and two
root branches in general.
• It contributes to esthetics and phonetics,
but is basically a grinding tooth.
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• The buccal outline is pentagonal
• Resembles the upper canine and the
second premolar.
• A little smaller than the canine and larger
than the 2. PM.
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• The mesial margin is build with the mesio-
occlusal slope an obtuse angle.
• The mesial outline is shallow concave from
the contact to the cervical line.
• The crest of curvature is located near the
junction between occlusal and middle
third.
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• The distal outline is slightly shorter than
the mesial.
• The disto-occlusal margin and the
concavity is less prominent.
• The crest of curvature is more cervically
located.
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• The occlusal outline is similar to the upper
canine
• the cusp tip is less prominent than canine but
more than 2. PM
• The cusp tip divides the buccal surface into
unequal halves
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• Before attrition and wear, the mesio-occlusal
slope is longer and straighter, the distoocclusal shorter and more curved
• The cusp tip is offset to distal
• The buccal developmental grooves extend
occlusaly and cause a concavity or notch on
the occlusal margins.
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• The cervical outline is convex toward the apex,
but less than anterior teeth
• The buccal ridge, comparable with the canines,
extends from the cusp tip halfway on the buccal
surface.
• The mesiobuccal and distobuccal developmental
grooves are present on each side of the buccal
ridge.
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• The imbrication lines are a common feature
• The height of contour is cervically located.
J. Naim-Faculty of
Dentistry-University of
Palestine
Lingual Aspect
• Smoothly convex in all directions
• The crown tapers lingually, so the lingual surface
is smaller than the buccal
• The lingual cusp tip is offset mesially, so both
cusp tips are visible from this view.
• The proximal outlines are shorter than that of
the buccal and are normally convex
J. Naim-Faculty of
Dentistry-University of
Palestine
Lingual Aspect
• The cusp tip is offset mesially and not sharply
pointed.
• It is 1 mm shorter than the buccal cusp, the
shortest cusp in the upper premolars.
• The mesio-occlusal slope is shorter than the
disto-occlusal slope
J. Naim-Faculty of
Dentistry-University of
Palestine
Lingual Aspect
• The cervical line is curved toward the apex
• The height of contour is located in the middle
third
• No pits, no grooves, no depressions
J. Naim-Faculty of
Dentistry-University of
Palestine
Mesial Aspect
• The general shape is trapezoidal
• The buccal margin is generally convex with
the height of contour cervical
• The lingual margin is an even arc with the
with the height of contour at the middle third
• The occlusal margin is irregular concave.
J. Naim-Faculty of
Dentistry-University of
Palestine
Mesial Aspect
• The mesial marginal ridge makes up the
majority of this surface
• A mesial marginal groove intends the occlusal
margin two-thirds of the way from buccal to
the lingual outline
• The cervical margin is irregular convex toward
occlusal, equal to the distal of the canine and
less than the anterior teeth.
J. Naim-Faculty of
Dentistry-University of
Palestine
Mesial Aspect
• From this aspect we could observe the
difference between the cusps
• The mesial concavity is a typical landmark for
first upper premolars to distiguish them from
the second upper premolars
• This concavity varies in its extents from the
middle portion of the cervical area, but could
reach the occlusal margin.
J. Naim-Faculty of
Dentistry-University of
Palestine
Mesial Aspect
• The height of contour is associated with the
contact area
• It is located near the junction of the middle
and occlusal thirds
• The contact area is roughly circular in shape
and is offset to the buccal.
J. Naim-Faculty of
Dentistry-University of
Palestine
Distal aspect
• Similar to the mesial surface but slightly
shorter occlusocervically.
• The distal surface is generally convex in all
directions and does not exhibit the concavity
which is present on mesial surface.
J. Naim-Faculty of
Dentistry-University of
Palestine
Distal aspect
occlusal margin:
• similar to the mesial aspect except that the
marginal ridge is located at a more cervical
level.
• There is normally no marginal groove.
Cervical margin : the curvature is less than
the mesially.
J. Naim-Faculty of
Dentistry-University of
Palestine
Distal aspect
Contact Area:
• Larger than mesial and is located at slightly
more cervical level, but still at the junction of
the occlusal and middle thirds.
• The outline of contact area is ovoid and is
wider buccolingually than occlusogingivally.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
• The outline of the crown is hexagonal (six-
sided)
• It is wider buccolingually than mesiodistally.
Boundaries:
• The occlusal table is bounded on the mesial and
distal by the marginal ridges.
• Buccal and lingual: by the mesial and distal
cusp ridges of the buccal and lingual cusps .
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
Buccal outline:
• Convex
• The prominent buccal ridge is the primary
contributor to the general convexity.
• There are slight concavities in the outline on
either side of the buccal ridge, the buccal
developmental depressions.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
Mesial and distal margins:
• Both proximal margins are relatively straight,
and they converge toward the lingual.
• So the lingual portion of the tooth is narrower
mesiodistally than the buccal portion.
- When the mesial margin groove is prominent, it
may create a dip in the mesial outline .
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
• 2 Cusps
• Transverse ridge
• Marginal ridges
• 2 Fossae
• Pits and Grooves
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
1. Buccal cusp:
• It is normally sharper, longer and bulky
• It is wider and higher than the lingual cusp.
• The buccal cusp tip is located well toward the
buccal and is offset to the distal.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
1. Buccal cusp:
The buccal cusp has four cusp ridges .
• buccal cusp ridge
• lingual cusp ridge
• mesial cusp ridge
• distal cusp ridge
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
lingual cusp ridge =
buccal triangular ridge
of the tooth =
buccal portion of the
transverse ridge
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
• The mesial cusp ridge and distal cusp
ridge correspond to the mesio-occlusal
and disto-occlusal slopes, which
compose the occlusal outline from
buccal aspect.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
• The buccal cusp has four inclined planes which are the
sloping area located between two adjacent cusp ridges.
• They take the name of the two
cusp ridges which they lie
between .
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
• Mesiobuccal inclined plane
• Distobuccal inclined plane
• Mesolingual inclined plane
• Distolingual inclined plane
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
lingual cusp:
• It is generally smaller and more rounded than the buccal
cusp.
• The lingual cusp tip is located well to the lingual and is
offset toward the mesial.
• It is the shortest of all the maxillary premolar cusps
• It has also four cusp ridges and four inclined planes.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
Another characteristic that is representative of all posterior
maxillary teeth is that the tips of the cusps are well within
the confines of the root trunk.
In other words, the measurement from the tip of the buccal
cusp to the tip of the lingual cusp is less than the
buccolingual measurement of the root at its cervical
portion.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
Transverse ridge:
• The buccal and lingual
triangular ridges of the tooth
meet in the area of the central
groove, thus forming the
transverse ridge.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
Marginal ridges:
They are linear ridges which run
from the bucco-occlusal point
angle to the lingo-occlusal
point angle and are named
mesial and distal marginal
ridges.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
Marginal ridges:
The mesial marginal ridge is
normally slightly shorter, and
its continuity is interrupted by
the mesial marginal groove.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
Fossae:
Fossae are the general depressed
areas on the occlusal surfaces
of posterior teeth.
The maxillary premolars
normally display two fossae,
mesial &distal triangular fossa.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
Pits and Grooves:
• The occlusal surface normally
exhibits two pits, the mesial &
distal pit.
• They are located in the deepest
portion of two fossae.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
Mesial pit: It is the point of union of four developmental
grooves:
• Central gr.
• Mesiobuccal triangular gr.
• Mesiolingual triangular gr.
• Mesial marginal gr.
J. Naim-Faculty of
Dentistry-University of
Palestine
Components of the Occlusal table
Distal pit: It is the point of union of three developmental
grooves:
• Central gr.
• Distobuccal triangular gr.
• Distolingual triangular gr.
J. Naim-Faculty of
Dentistry-University of
Palestine
J. Naim-Faculty of
Dentistry-University of
Palestine
Root
• There are two branches in the majority of cases, while
all other premolars are normally single rooted.
• Two roots are most found in this Tooth.
• There are three identifiable root types:
 Type I : single root
 Type II: bifurcated root
 Type III : laminated root
J. Naim-Faculty of
Dentistry-University of
Palestine
Root/Type I
• The single root is quite straight.
• It tapers fairly evenly from the cervical line
to the apex .
• It is wider buccolingually than mesiodistally
• Buccal and lingual surfaces are convex .
J. Naim-Faculty of
Dentistry-University of
Palestine
Root/Type I
• Buccal portion is slightly wider than the
lingual.
• Mesial and distal surfaces are normally
concave but the mesial is more, and
continuous with the mesial concavity
forming a longitudinal groove on the mesial
surface of the root.
J. Naim-Faculty of
Dentistry-University of
Palestine
Root/Type I
• In the cross section at mid root the outline is
often kidney shaped.
• The outlines of buccal and lingual are
convex.
• The outline of distal surface is flat to slightly
concave.
• The outline of mesial surface is concave.
J. Naim-Faculty of
Dentistry-University of
Palestine
Root/Type II
• Bifurcated root
• Root trunk is the portion of the root
between the cervical line and the point of
furcation .
• Root trunk is found only in multirooted
teeth.
• The root trunk divides into a buccal and
a lingual root branch.
J. Naim-Faculty of
Dentistry-University of
Palestine
Root/Type II
• All surface of both root branches are
convex.
• The buccal branch is normally larger in
general size
• Both roots are normally equal in length.
J. Naim-Faculty of
Dentistry-University of
Palestine
Root/Type II
In the cross section at the mid root level:
•
Both roots are round in outline.
•
The buccal root outline slightly greater in
circumference.
•
This is the most common root form of
maxillary first premolars.
J. Naim-Faculty of
Dentistry-University of
Palestine
Root/Type II
J. Naim-Faculty of
Dentistry-University of
Palestine
Root/Type III
• laminated root
• This type resemble type II, except that the
buccal and lingual branches are joined totally
or in part by a lamination.
• Lamination : thin connection between the
main portions of the root.
• In cross section: hourglass outline
J. Naim-Faculty of
Dentistry-University of
Palestine
Variations and anomalies
• Occasionally a three rooted specimen are found.
• Two buccal branches and one lingual branch.
• Rarely the root(s) penetrate the anterior
portion of The maxillary sinus.
J. Naim-Faculty of
Dentistry-University of
Palestine
Variations
and
anomalies