Lower First Premolar

Ist Dental Students - Morphology

1. ميحرلا نمحرلا لا مسبميحرلا نمحرلا لا مسب

2. Mandibular first premolarMandibular first premolar

3. chronologychronology

11
stst
evidence of calcification: 1 ¾ : 2 years evidence of calcification: 1 ¾ : 2 years

Crown completed: 5-6 yearsCrown completed: 5-6 years

Eruption: 10-12 yearsEruption: 10-12 years

Root completed:12-13 yearsRoot completed:12-13 years

4. Characteristics which resemble the Characteristics which resemble the
mandibular caninemandibular canine
11- - The buccal cusp is long and sharp. It is The buccal cusp is long and sharp. It is
the only occluding cuspthe only occluding cusp..
22- - the B L measurement is similar to that the B L measurement is similar to that
of mand canineof mand canine..
33- - The occlusal surface slopes linguallyThe occlusal surface slopes lingually..
44- - the outline from occlusal aspect the outline from occlusal aspect
resembles the outline from incisal resembles the outline from incisal
aspect of mand canineaspect of mand canine
44- - the mesio buccal cusp ridge is shorter the mesio buccal cusp ridge is shorter
than the disto buccal cusp ridgethan the disto buccal cusp ridge..

5. Characteristics which resemble the Characteristics which resemble the
mand 2nd premolarmand 2nd premolar

1-the outline of crown and root resembles that 1-the outline of crown and root resembles that
of mand 2nd premolar from the buccal aspect.of mand 2nd premolar from the buccal aspect.

2- M and D contact areas are nearly at the 2- M and D contact areas are nearly at the
same levelsame level

3- curvature of cervical line mesially and 3- curvature of cervical line mesially and
distally are the same.distally are the same.

4-it has more than one cusp. 4-it has more than one cusp.

7. Buccal aspectBuccal aspect
* the crown is roughly trapezoidal (the shorter * the crown is roughly trapezoidal (the shorter
being at the cervix) being at the cervix)
* * mesial contact area is straight or slightly concave mesial contact area is straight or slightly concave
from cervical line till the M CAfrom cervical line till the M CA
* * M contact area is broad and and present just M contact area is broad and and present just
cervical to the junction of the mid and occ thirdcervical to the junction of the mid and occ third..
* * D outline is slightly concave from the cervical D outline is slightly concave from the cervical
line till the area of contactline till the area of contact
* * CA distally is broader than mesially and present CA distally is broader than mesially and present
just cervical to the junction of the mid and occ just cervical to the junction of the mid and occ
third ( CAs at the same levelthird ( CAs at the same level((
* * M slope is shorter than the distal slope and the tip M slope is shorter than the distal slope and the tip
of the buccal cusp is mesial to the center of the of the buccal cusp is mesial to the center of the
crown. It is pointedcrown. It is pointed. .

8. 
M slope has shown some concavity M slope has shown some concavity
while distal slope usually shows while distal slope usually shows
concavityconcavity

Cervical line is convex root wise Cervical line is convex root wise

Crown is narrower MD at the cervix Crown is narrower MD at the cervix
when compared with the MD width at when compared with the MD width at
the CAthe CA

B surface is more convex than that of B surface is more convex than that of
max premolars specially at the cervical max premolars specially at the cervical
and mid third. and mid third.

9. 
B ridge is well developed and B ridge is well developed and
extend from cervical third to the extend from cervical third to the
cusp tip.cusp tip.

Developmental depressions are Developmental depressions are
seen between the 3 lobes.seen between the 3 lobes.

Root is shorter than that of Root is shorter than that of
mand canine by 3-4 mmmand canine by 3-4 mm

B surface of the root is smooth B surface of the root is smooth
and convexand convex

Root tapers and has pointed Root tapers and has pointed
apex. apex.

11. Lingual aspectLingual aspect::

Crown is trapezoidal in shape with the Crown is trapezoidal in shape with the
shorter side toward the cervical third.shorter side toward the cervical third.

Crown and root taper lingually. So Crown and root taper lingually. So
most of the M and D outlines of the most of the M and D outlines of the
lingual and buccal surface could be lingual and buccal surface could be
seen. seen.

Lingual cusp is shorter than buccal Lingual cusp is shorter than buccal
cusp (2/3) the major portion of the cusp (2/3) the major portion of the
crown is made up of the middle buccal crown is made up of the middle buccal
lobe.lobe.

Lingual cusp has a pointed tip (it Lingual cusp has a pointed tip (it
resemble a well developed cingulum)resemble a well developed cingulum)

12. 
Lingual cusp is on a line with the Lingual cusp is on a line with the
buccal triangular ridge.buccal triangular ridge.

The ML dev groove divides the lingual The ML dev groove divides the lingual
cusp into 2 parts (lobes) smaller on cusp into 2 parts (lobes) smaller on
the mesial side , larger on the distal the mesial side , larger on the distal
side.side.

2 dev grooves on the M and D side 2 dev grooves on the M and D side
making the mesial and distal fossa making the mesial and distal fossa
( no triangular fossa since the shape is ( no triangular fossa since the shape is
not triangular)not triangular)

The CA and MRs are pronounced . The CA and MRs are pronounced .
the CA are broad.the CA are broad.

Cervical portion of the crown is Cervical portion of the crown is
narrow and convex.narrow and convex.

13. Roots tapers lingually and Roots tapers lingually and
there is a narrow ridge w is there is a narrow ridge w is
smooth and convex. This allow smooth and convex. This allow
the M and d surface to be seen.the M and d surface to be seen.
Root tapers from the cervix to Root tapers from the cervix to
the pointed apex.the pointed apex.
The occ surface slopes toward The occ surface slopes toward
the lingual side . most of the the lingual side . most of the
occ surface of this tooth can be occ surface of this tooth can be
seen from this aspect. The seen from this aspect. The
cervical line is convex root cervical line is convex root
wise.wise.

15. Mesial aspectMesial aspect

Crown outline is rhomboidal in shapeCrown outline is rhomboidal in shape

Buccal outline of the crown is convex Buccal outline of the crown is convex
from cervical line till the cusp tip. from cervical line till the cusp tip.

Crest of curvature is present just Crest of curvature is present just
below the junction of the mid and below the junction of the mid and
cervical third.cervical third.

The lingual outline (represented by The lingual outline (represented by
the lingual cusp) is convex from the the lingual cusp) is convex from the
cervical line till the tip of the cusp.cervical line till the tip of the cusp.
(the convexity is less than the buccal (the convexity is less than the buccal
outline).outline).

The crest of curvature lingually The crest of curvature lingually
approaches the mid third of the approaches the mid third of the
crown.crown.

The tip of the buccal cusp is centered The tip of the buccal cusp is centered
over the root. It may be a little buccal over the root. It may be a little buccal
to the center.to the center.

16. 
On the other hand, the tip of the On the other hand, the tip of the
lingual cusp is on a line with the lingual cusp is on a line with the
lingual border of the root.lingual border of the root.

It must be noted that the crest of It must be noted that the crest of
curvature of the lingual surface is out curvature of the lingual surface is out
of the lingual outline of the root. ( the of the lingual outline of the root. ( the
convexity of the lingual outline of the convexity of the lingual outline of the
lingual lobe is lingual to the lingual lingual lobe is lingual to the lingual
outline of the root).outline of the root).

The lingual cusp is 2/3 of the buccal The lingual cusp is 2/3 of the buccal
cusp, so the buccal cusp is the only cusp, so the buccal cusp is the only
occluding cusp.occluding cusp.

Cervical line is concave root wise. It Cervical line is concave root wise. It
is regular with average 1 mm depth.is regular with average 1 mm depth.

The mesial marginal ridge is parallel The mesial marginal ridge is parallel
to the buccal triangular ridge.to the buccal triangular ridge.

On the mesiolingual lobe there is a On the mesiolingual lobe there is a
depression (DD) . this depression depression (DD) . this depression
harbors the mesiolingual dev groove. harbors the mesiolingual dev groove.

17. 
The mesial surface of the crown is The mesial surface of the crown is
smooth except for the mesiolingual smooth except for the mesiolingual
dev groove,(MLDG).dev groove,(MLDG).

At the mesial CA , the surface is At the mesial CA , the surface is
convex , below the CA , the surface convex , below the CA , the surface
is concave till the cervical line.is concave till the cervical line.

The root outline from the mesial The root outline from the mesial
aspect is parallel till the apical 1/3 , aspect is parallel till the apical 1/3 ,
then it tapers giving a pointed apex then it tapers giving a pointed apex
(lined with the buccal cusp).(lined with the buccal cusp).

The mesial surface of the root is The mesial surface of the root is
smooth till the mid third except for smooth till the mid third except for
the presence of a deep DG.the presence of a deep DG.

The root may be bifurcated in this The root may be bifurcated in this
area. area.

19. Distal aspectDistal aspect

Distal surface is the reverse Distal surface is the reverse
picture of mesial one with picture of mesial one with
some differences:some differences:

DMR is higher above the DMR is higher above the
cervixcervix

It does not slope lingually It does not slope lingually
but it is horizontal and but it is horizontal and
perpendicular to the axis perpendicular to the axis
of crown and root.of crown and root.

DMR is confluent with the DMR is confluent with the
lingual cusp ridgelingual cusp ridge

No DLDG No DLDG

20. Curvature of cervical line mesially is less than Curvature of cervical line mesially is less than
distallydistally
CA are broader distally than mesially CA are broader distally than mesially
Distal surface of the root exhibits more Distal surface of the root exhibits more
convexityconvexity
A shallow DD is centered on the root but it A shallow DD is centered on the root but it
does not contain deep DG. does not contain deep DG.

22. Occlusal surfaceOcclusal surface

Occ aspect may be diamond or Occ aspect may be diamond or
circular in shapecircular in shape

The mand 1st premolars have The mand 1st premolars have
similar characteristics when similar characteristics when
viewed from the occ aspect either viewed from the occ aspect either
it was diamond or circular.it was diamond or circular.

1- mid buccal lobe make the 1- mid buccal lobe make the
greatest bulk of the toothgreatest bulk of the tooth

2-buccal ridge is prominent2-buccal ridge is prominent

3- MB and DB line angles are 3- MB and DB line angles are
rounded (MB& DB)rounded (MB& DB)

4-D and M contact areas are 4-D and M contact areas are
broad ( Distal is broader)broad ( Distal is broader)

Crown converge sharpely to the Crown converge sharpely to the
lingual surfacelingual surface

Lingual cusp is smallerLingual cusp is smaller

23. 
MR are well developedMR are well developed

B triangular ridge is heavy while B triangular ridge is heavy while
lingual triangular ridge is smalllingual triangular ridge is small

On the occ surface there are 2 On the occ surface there are 2
depressions:depressions:

Mesial (linear) fossa and distal Mesial (linear) fossa and distal
(circular fossa) (circular fossa)

M fossa harbors a groove called M fossa harbors a groove called
mesial DG. It is linear in shape.mesial DG. It is linear in shape.

D fossa harbors another crescentric D fossa harbors another crescentric
groove called DDG.groove called DDG.

Also, there is the distal D pit and Also, there is the distal D pit and
another groove called MLDG another groove called MLDG
which crosses the lingual cusp & which crosses the lingual cusp &
appear on the lingual surface. appear on the lingual surface.
Radiating supplemental grooves Radiating supplemental grooves
may appear from the occ aspect may appear from the occ aspect
radiating from the DG. radiating from the DG.

26. THANK YOUTHANK YOU