Human dentition Dr. Hazem Al Ajrami First Year in Dentistry First Semester Al-Azhar University - Gaza Lama El Banna

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College of DentistryCollege of Dentistry
Human Dentition IIHuman Dentition II
Deciduous Posterior Teeth - 02Deciduous Posterior Teeth - 02
Dr. Hazem Al AjramiDr. Hazem Al Ajrami

3. Deciduous Mandibular Molars

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5. Deciduous Mandibular First Molar
It is the predecessor of the mandibular first
premolar.
This tooth does not resemble any of the other
teeth, deciduous or permanent. Because it
varies so much from all others, it appears
strange and primitive.
It usually has four cusps (two buccal and two
lingual cusps) and two roots (mesial and distal
roots).

6. Buccal Aspect
Outline form: trapezoid.
Mesial and distal outlines: the mesial contour
of the crown is nearly straight, whereas the
distal side is convex and converges markedly
toward the cervix. The mesial contact area
with the canine is located more occlusally than
the distal contact area that is present in the
middle of the crown.

8. Occlusal outline: the mesiobuccal cusp is
much wider than the distobuccal cusp with no
groove between them, just a depression. The
mesiobuceal cusp occupies nearly two thirds
of the buccal surface. The buccal cusps are
more pronounced than on the deciduous
maxillary first molar.

10. The cervical line is convex towards the root
and slopes occlusally from mesial to distal.
Thus the mesial portion of the crown is longer
than the distal.
The buccal surface has a very prominent
cervical ridge running horizontally at the
cervical third with the most prominent part is
present mesially.

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12. Roots: there are two roots; mesial and distal.
The mesial root is often wider and longer than
the distal root.
The roots are widely spread and slender, and
the furcation is close to the cervical line.

13. Lingual Aspect
The mesiolingual cusp is larger, longer, and
sharper than all the other cusps.
There is a slight lingual groove between the two
lingual cusps.
The mesial marginal ridge is so well developed
that it resembles a cusp.
The cervical line is nearly straight. So, the crown
length is nearly equal mesially and distally.
The lingual surface is narrower than the buccal
due to the lingual convergence.

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15. This surface is convex mesiodistally and
cervico-occlusally.
The root trunk may be longer than it is on the
buccal side.
The roots are narrower lingually.

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17. Mesial Aspect
Outline form: rhomboidal.
Buccal outline: the buccal outline is extremely
convex at the cervical third representing the
most prominent mesiohuccal cervical ridge
then the buccal outline becomes straight till
the tip of the mesiobuccal cusp. The buccal
outline of the crown is longer than the lingual,
placing the mesiobuccal cusp well within the
root base.

19. The lingual outline is convex with the
maximum convexity is present in the middle
third. It extend lingually beyond the confines
of the root base. The mesiolingual cusp tip
may be even with or outside the lingual
margin of the root. The crown appears to
incline toward the lingual surface.

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21. Occlusal outline: the occlusal table is small
buccolingually.
Both the mesiobuccal and the mesiolingual
cusps are seen from this aspect, as is the well-
developed mesial marginal ridge.
The cervical line is convex toward the
occlusal. It slants occlusally from buccal to
lingual.

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23. The mesial surface of the crown is relatively
flat buccolingually and cervico-occlusally.
Root: the mesial root outlines are straight from
the neck till the apical third, then it tapers to
end in a flat and broad apex. The root has a
depression on most of its length.

24. Distal Aspect
The buccal cervical ridge is less prominent
from the distal side than from the mesial
side.
The crown has an almost equal length
buccally and lingually.
The distobuccal and distolingual cusps are
nearly the same height but much shorter than
the mesial cusps.

25. The distal marginal ridge is short
buccolingually, is less prominent than the
mesial marginal ridge, and is located more
cervically so more of the occlusal surface is
seen.
The cervical line is almost straight.
The distal root is more rounded, less broad,
thinner, and shorter than the mesial root.

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27. Occlusal Aspect
Outline form: rhomboid.
The crown is much wider mesiodistally than
buccolingually.
The mesiobuccal angle is acute and
prominent because of the mesiobuccal
cervical ridge on the buccal surface. The
distobuccal angle is obtuse.

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29. Cusps & ridges:
The cusps are often difficult to distinguish, but
careful examination of an unworn tooth will
reveal (in order of diminishing size),
mesiobuccal, mesiolingual, distobuccal, and
the smallest (also shortest) distolingual cusp.
The mesiolingual cusp is pointed, and angled
in on the occlusal table.
Mesial and distal marginal ridges are well
developed with the mesial is more prominent
than the distal one.

30. Fossae, grooves and pits:
The occlusal anatomy is shallow.
There is a small mesial triangular fossa with a
mesial pit and a larger distal fossa extends
almost into the center of the occlusal surface.
There is no central fossa.

31. A central developmental groove arises from the
central pit in the distal half of the occlusal
surface separating the mesiobuccal and
mesiolingual cusps and ending in the mesial pit.
There is a short buccal groove and a short
lingual groove extending from the central pit.
The buccal groove separates the mesiobuceal
and the distobuccal cusps and does not extend
onto the buccal surface. The lingual groove
separates the mesiolingual and the distolingual
cusps and does not usually extend to the lingual
surface, but ends as a shallow depression on the
lingual surface.

32. There are two supplemental grooves join the
developmental groove in the center of the
mesial triangular fossa; one groove extends
buccally and the other extends lingually.
There are some supplemental grooves
immediately mesial to the distal marginal ridge
in the distal triangular fossa, which join the
central developmental groove.

33. Deciduous Mandibular Second Molar
It is the predecessor of the mandibular second
premolar.
The deciduous mandibular second molar is
larger than the first one, but it is smaller than
the permanent mandibular first molar.
However, it resembles the permanent
mandibular first molar in many ways such as:

35. The outline form of all aspects of the two teeth
is the same.
The number of cusps (five cusps), the number
of roots (two roots) is the same.
All the elevations and depressions that are
present in the permanent mandibular first
molar are present in this tooth. It is reported
that the first permanent molar is sometimes
mistaken for this tooth and is not restored
when decayed on the assumption that it will
soon be shed and replaced by another tooth.

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37.  However, there are many differences that
enable us to differentiate between these two
teeth such as:
 The general differences between the deciduous
and permanent teeth that were mentioned
before (e.g. size, colour, bulbous crown,
prominent cervical ridge, thin and divergent
roots, and absence of root trunk).
 The three cusps on the buccal surface of the
deciduous first molar are of nearly equal size
and are named; mesiobuccal, buccal and
distobuccal cusps. (Compare with cusps of the
permanent first mandibular molar).