- The term "bicuspid" is often used for of premolar, but
this is inaccurate since the mandibular second premolar
may show three cusps.
- There are eight premolars-two in each quadrant .They are
successors for the deciduous molars.
- The premolars are neighbored mesially by the canines
and distally by the molars. They erupts following the
shedding of their predecessors(deciduous molars).
- The premolars are developed from four lobes, three
buccal lobes ( the three form the buccal cusp) and one
lingual ( for the single lingual cusp), except the
mandibular second premolar (the three cusp form) in
which it develops from five lobes, three buccal and two
lingual( as it has two lingual cusp).
- Usually the first premolars assist the canines in their
function of tearing.While the second premolars assist the
molars in their grinding function.
- Premolars resembles canine yet the main differences are:
Ass. Prof. /Reham Magdy1
It resembles the canine from the buccal aspect, but differs in that:
Less curvature of the cervical
line mesially and distally.
Cervical line is more curved
mesially and distally
The contact areas are about the
Contact areas with different levels
They have occlusal surface . They have incisal ridges
Greater relative buccolingual measurement as compared with the
mesiodistal measurement than that of the canine. Premolars has
shorter crown cervico-occlusal .
Marginal ridge is found mesial
and distal to the occclusal surface.
Marginal ridge is found mesial
and distal to the lingual surface
The mesial slope of the buccal
cusp of the first premolars is
longer than the distal slope
The distal slope of the canines
is longer than the mesial slope
The root is shorter The roots are longer
Ass. Prof. /Reham Magdy2
THE MAXILLARY FIRST PREMOLAR
* This tooth is the usually has two roots (about 80%) a
buccal and a lingual with two pulp canals. While in (20%) of the
cases it has single root.
- The maxillary first premolar has two well developed cusps ,
buccal and lingual. The buccal cusp is longer than the lingual cusp by
about 1 m.m.
Appearance of dental organ 7 m.I.U.
First evidence of calcification 1 - 1 year
Enamel completed 5-6 years
Eruption 10-11 years
Root completed 12-13 years
*Geometrical outline : The crown is roughly
trapezoid with the smallest uneven sides directed
The mesial outline of the crown is slightly concave
from the cervical line to the mesial contact area which
is present slightly cervical to the occlusal third ( about
junction level) . Also mesial cusp slope is concave and
longer than distal one.
Ass. Prof. /Reham Magdy3
The distal outline is less concave till the contact area. The
contact distally is broader than the mesial, and tends to be more
occlusal.The distal slope is slightly convex.
The buccal cusp is long and located distal to the midline ( as the
mesial slop is longer)
*The cervical line :The cervical line is curved rootwise.
The buccal surface has a cervical ridge present in the cervical
third of the buccal surface. The crown surface is convex, with a
continuous ridge from the cusp tip to the cervical margin which is
called the buccal ridge. This ridge denotes strong development of
the middle buccal lobe.
Two developmental grooves, the mesiobuccal and distobuccal,
are located on both sides of the buccal ridge and mark the union of the
*Roots: The buccal root outline resembles that of the maxillary
canine but is shorter .
-The crown converges lingually . The lingual cusp
is shorter and narrower mesiodistally than the buccal
cusp. Since the lingual cusp is shorter than the buccal
cusp, the tips of both cusps with their mesial and distal
slopes may be seen from this aspect.
-The mesial and distal outlines , as well as mesial
and distal slopes of the lingual cusp are convex.
-The tip of the lingual cusp is pointed and located slightly
Ass. Prof. /Reham Magdy4
-The mesial slope of the lingual cusp is shorter than the distal
-The crown is smooth and convex with no definite lingual ridge
and no developmental grooves.
The lingual height of contour is located at the middle third.
The cervical line lingually is slightly curved with the crest of
curvature on the center of the root.
The lingual root is smooth convex with the apex directed distally
. As the lingual root is narrower so buccal root outline appears from
*In single rooted teeth, the root tapers till a pointed apex.
Mesial aspect :
* Geometric form:
It is trapezoidal in shape; however the longest of the uneven
sides is toward the cervical portion and the shortest toward the
The buccal outline of the crown is convex with the crest of
curvature within the cervical third (The cervical ridge). It continues
less convex to the tip of the buccal cusp. The tip of the buccal cusp is
located directly below the center of the buccal root.
Ass. Prof. /Reham Magdy5
The lingual outline is curved smoothly from the cervical line to
the tip of the lingual cusp. The crest of this curvature is near the
center of the middle third.
The tip of the lingual cusp is on a line with the lingual border of
the lingual root.
The lingual cusp is always shorter than the buccal cusp by about
1 m.m. The mesial marginal ridge is convex and is located at about
the level of the junction of the middle and occlusal third.
The mesialcontact area is circular in shape, located at the
junction of the middle and occlusal thirds and slightly near the buccal.
The distinguishing features of this tooth from the mesial aspect
1- The canine fossa: The presence of the Mesial developmental
depression which extends cervically from the contact area and
continues up to include the cervical line then joins a deep
developmental depression between the root bifurcation .
Ass. Prof. /Reham Magdy6
2- The mesial marginal developmental groove : The presence
of well defined developmental grooves in the enamel of the
mesial marginal ridge. The marginal groove extend from the
central groove of the occlusal surface of the crown, crossing
the marginal ridge just lingual to the contact area and
terminating a short distance cervical to the mesial marginal
ridge. groove is called the
3- The root trunk is long on the distal than mesial. Thus the
furcation on the mesial side is found on the middle third, while
disatally in the apical third.
4- The mesial surface of the root trunk with a deep developmental
groove and depression. In case of one rooted tooth, this
depression is noticeable for most of the root length.
It resemble the mesial except for:
-The distal contact area is larger and more occlusally located
than the mesial contact area and also slightly near to the buccal.
- The curvature of the cervical line is less on the distal than on
the mesial surface ( it may be straight line).
-There is no deep developmental groove crossing the distal
marginal ridge as in the mesial .
- The root trunk with no developmental depression.
- The bifurcation of the root is near the apical third .
Ass. Prof. /Reham Magdy7
Geometrical outline: The occlusal aspect is
roughly a six-sided or hexagonal figure (two
equal buccal sides, Mesial side, shorter than distal
and the mesiolingual is shorter than the
It is wider buccolingually than mesiodistally.
Narrower lingually than buccally.
- The occlusal surface shows two well-developed cusps. The
buccal cusp is larger than the lingual one.
Each cusp has distal cusp ridge and mesial cusp ridge. Also
cusps triangular ridges extend from cusp ridge to the central groove
The buccal ridge descends from the cusp tip cervically onto the
Also there are two marginal ridges ( mesial and distal) found on
both sides of the occlusal surface.
- Just inside the mesial and distal marginal ridges are the mesial
and distal triangular fossae.
- The mesial and distal developmental pit are present on he
depth of the triangular fossea..
- A well-defined central developmental groove divides the tooth
mesiodistally. It extends from a point just mesial to the distal
marginal ridge to the mesial marginal ridge where it joins the mesial
Ass. Prof. /Reham Magdy8
marginal developmental groove. This latter crosses the mesial
marginal ridge and ends on the mesial surface of the crown.
Two grooves join the central groove extending on both sides of
the mesial and distal triangular fossae. These are called the
mesiobuccal and distobuccal developmental grooves.
* No supplemental grooves are present in most cases.
The pulp cavity
The buccolingual section
The pulp chamber is broad buccolingually with well developed
pulp horns in its roof. The wide pulp chamber presents and leading
into the root canals.
The premolars double rooted have two pulp canals. The single
rooted could have one or two root canals. The lingual root canal is
larger than the buccal. The root canals taper evenly from the floor of
the pulp chamber to the apical foramen.
The Mesiodistal section : is similar to the pulp cavity of the
maxillary canine. It is relatively narrow with an even taper from the
pulp chamber to the root end.
A transverse section at the cemento-enamel junction shows the
characteristic kidney shaped root trunk. The root form cervically is
wider buccolingually than mesiodistally.
Ass. Prof. /Reham Magdy9
MAXILLARY SECOND PREMOLAR
The maxillary second premolar supplements the maxillary first
premolar in function and resemble it except of the following
̵ It is single rooted (85%) with less angular and rounded crown
from all aspects.
̵ The crown of the second premolar is shorter cervico-occlusally.
The root, however, is little longer.
̵ The maxillary second premolar is generally smaller in size
comparing the maxillary first premolar.
Appearance of dental organ 8 m .I.U.
First evidence of calcification 2- 2 years
Enamel completed 6-7 years
Eruption 10-12 years
Root completed 13-15 years
-The buccal cusp of the second premolar is shorter and appears
-The mesial slope of the buccal cusp is usually shorter than the
distal slope, which is the opposite for the first premolar.
Ass. Prof. /Reham Magdy11
The lingual cusp is almost the same length as the buccal cusp
( which differs than the first premolar).
-The buccal and lingual cusps are nearly the same length.
-There may be greater distance between the cusp tips which
widens the occlusal surface buccolingually.
-The crown surface is convex with no developmental
depression. Only a shallow developmental groove appears on the
single tapered root.
-There is no deep developmental groove crossing the mesial
There is no variation noted except for the root variations.
Ass. Prof. /Reham Magdy12
-The outline of the crown is more rounded
or oval, rather than angular.
-There is a wide distance between the cusp
tips buccolingually, and the lingual cusp is almost
as wide as the buccal cusp.
-The central developmental groove is shorter
mesiodistally and with multiple supplemental
grooves radiating from the central groove.
-The mesial and distal triangular fossae are
nearer to each other.
-The marginal ridges are thicker. .
Ass. Prof. /Reham Magdy13
THE PULP CAVITY
There is a wide pulp chamber with two well defined pulp horns.
There are two pulp canals, one buccal one lingual. The pulp
cavity is very broad at its junction with the pulp chamber, then it
narrows gradually until reaching the mid-root, then constricts rapidly
to the apex.
A characteristic feature of the pulp cavity from this section is
that it may show single broad pulp canal divided at mid-root into two
canals by Dentin Island, and then the canals join again near the
Similar to that of the maxillary first molar.
Cervical cross section
A cervical cross section may display an oval root trunk instead
of the kidney shaped root trunk of the first premolar.
Ass. Prof. /Reham Magdy14