Introduction to Dentistry 11
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
Chronology & Measurements
J. Naim-Faculty of
Dentistry-University of
Palestine
General
• There are two general types for lower 2. Premolar:
▫ The most common type with two lingual cusps
▫ The other type displays one cusp.
• The occlusal table is most similar to that of a molar.
• This tooth functions in a grinding capacity with the
molars, as contrasted to the first premolar which
functions much like the canine.
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
The mandibular second premolar resembles
the mandibular first premolar from the
buccal, with the following exceptions:
• The tooth is slightly larger, even though
the tip of the buccal cusp is shorter and the
occlusocervical dimension is a little less.
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m
J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• The cusp tip is not so high, not as sharp as
the 1. premolar.
• The mesio-occlusal and disto-occlusal
slopes are not as inclined.
• The cusp tip is also centered mesiodistally,
making the two slopes approximately
equal in length.
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J. Naim-Faculty of
Dentistry-University of
Palestine
Buccal Aspect
• Despite these slight differences, it is
difficult to distinguish between the two
mandibular premolars from this aspect.
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J. Naim-Faculty of
Dentistry-University of
Palestine
Lingual Aspect
• The lingual cusp or cusps, are better developed
and higher in comparison to the first premolar.
• The mesial, distal, and cervical outlines are
similar to those of the first premolar, although
the lingual surface is considerably wider
mesiodistally, and longer occlusocervically.
J. Naim-Faculty of
Dentistry-University of
Palestine
Lingual Aspect
Occlusal outline: The lingual cusps are higher,
and as a consequence, much less of the
occlusal surface can be seen from this aspect,
when compared to the first premolar.
The height of the lingual cusp(s) is still
somewhat less than the buccal cusp height.
J. Naim-Faculty of
Dentistry-University of
Palestine
Lingual Aspect
The three cusp type exhibits a mesiolingual
and a distolingual cusp, between them a lingual
groove extends a short distance onto the lingual
surface.
• The mesiolingual cusp is wider and longer,
while the distolingual cusp is smaller, but often
is the sharper of the two.
J. Naim-Faculty of
Dentistry-University of
Palestine
Lingual Aspect
• This arrangement leaves the lingual groove
offset to the distal in the occlusal outline.
J. Naim-Faculty of
Dentistry-University of
Palestine
Lingual Aspect
The two cusp type displays a single lingual
cusp.
• There is no lingual groove, but a depression is
often found toward the distal portion of the
surface.
J. Naim-Faculty of
Dentistry-University of
Palestine
Mesial Aspect
• From the mesial aspect, the two mandibular
premolars are similar
• Dimensionally, the second premolar is wider
buccolingually, but shorter occlusocervically
than the 1. premolar.
J. Naim-Faculty of
Dentistry-University of
Palestine
Mesial Aspect
Structurally, the two premolars differ in the
following ways:
•
The lingual inclination of the crown is not quite
as great as on the first premolar. Consequently,
the buccal cusp tip is not centered over the root,
but rather is buccal of center.
•
The buccal cusp tip is also shorter and less
sharp.
J. Naim-Faculty of
Dentistry-University of
Palestine
Mesial Aspect
•
Lingual cusps are more prominent than on
the first premolar.
•
Occlusogingivally, the mesial surface is convex
in the occlusal portion, and concave in the
gingival portion.
•
The contact area is located toward the buccal,
at the junction of the occlusal and middle
thirds.
J. Naim-Faculty of
Dentistry-University of
Palestine
Mesial Aspect
•
It is also roughly circular in outline.
•
The marginal ridge is nearly horizontal, and
much less of the occlusal surface is visible.
•
There is normally a mesial marginal groove
present.
•
The height of contour of the lingual margin is
found in the occlusal third, a location which is
unique to the mandibular second premolar.
J. Naim-Faculty of
Dentistry-University of
Palestine
Distal aspect
Similar to the mesial surface except in the following
ways:
• The distal marginal ridge is more cervically placed
than on the mesial resulting in more of the occlusal
surface being visible from this aspect, as well as a
shorter surface occlusocervically.
• In the three cusp type, the tips of both the
mesiolingual cusp and the distolingual cusp are
visible.
J. Naim-Faculty of
Dentistry-University of
Palestine
Distal aspect
• The contact area is similarly located, but
because it is shared with the first molar, it is
larger and somewhat ovoid, wider
buccolingually than occlusocervically.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
• The general shape of the crown
from this aspect is more nearly
square especially in the three cusp
type.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
General groove pattern: The occlusal groove
pattern is responsible for the names of the second
premolar types:
• The main groove pattern on the three cusp type
takes the form of a "Y", and it is thus named Y type.
• The main groove pattern on the two cusp type
resembles a " U or "H", resulting in U and H type.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
• The Y type is the most common form of mandibular second
premolar, and the two cusp types are less often seen, with
H type specimens more common than U type.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
Three cusp type - (Y type):
• The outline of the Y type from the occlusal aspect
is roughly square lingual to the buccal line angles.
• The Y pattern of the occlusal table is formed by a
combination of the central and lingual grooves.
• The three cusps vary in height and size from
largest to smallest, as follows: buccal,
mesiolingual, and distolingual cusp.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
• There is no transverse ridge on the Y type
second premolar.
• There are two fossae, the mesial and distal
triangular fossae.
• There are three pits present on the occlusal
table, mesial pit, distal pit and central pit.
• The central groove has a mesial and distal
portion.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
Two cusp type:
• Two cusp type second premolars exhibit a
rounded outline lingual to the buccal line angles.
• The mesial and distal surfaces may converge
somewhat more toward the lingual.
• The one lingual cusp is placed directly opposite
the buccal cusp and their respective triangular
ridges create a transverse ridge.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
• No lingual groove or central pit.
• The buccal cusp is larger and somewhat
higher than the lingual cusp.
• The lingual cusp sometimes appears as
an irregular convexity, rather than a
distinct cusp, especially in the U type.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
• The lingual cusp of the H type is larger and
sharper than in the U type, and on both types it
is offset to the mesial.
J. Naim-Faculty of
Dentistry-University of
Palestine
Occlusal aspect
• There are two fossae, mesial and distal
fossa
• In the U type the central groove is
crescent like and connect the two pits
together.
• In the H type the central groove is a short
line , which runs between the pits.
J. Naim-Faculty of
Dentistry-University of
Palestine
Root
• The root is normally single, and tapers evenly to the
apex which is relatively sharp.
• It often has a slight distal inclination in the apical third.
• The root is slightly wider and longer than that of the
first premolar.
• Like the 1. premolar the outline is roughly ovoid and
wider buccolingually than mesiodistally.
J. Naim-Faculty of
Dentistry-University of
Palestine
Variations and anomalies
• In three cusp type crowns, the comparative size of
the ML and DL cusps is quite variable. The DL cusp
ranges from a barely discernible bump to approximately
the same size as the ML cusp.
• Anomalies are rare, although a root bifurcation into
buccal and lingual branches is sometimes seen.
J. Naim-Faculty of
Dentistry-University of
Palestine
Variations and anomalies
• The mandibular second premolars are, on occasion,
congenitally missing, either unilaterally or
bilaterally.
• Supernumerary teeth are sometimes observed in
the mandibular premolar area.
J. Naim-Faculty of
Dentistry-University of
Palestine