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Page 1: Lower First Premolar

الرحمن الله الرحمن بسم الله بسمالرحيمالرحيم

Page 2: Lower First Premolar

Mandibular first premolarMandibular first premolar

Page 3: Lower First Premolar

chronologychronology

11stst 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

Page 4: Lower First Premolar

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..

Page 5: Lower First Premolar

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.

Page 6: Lower First Premolar
Page 7: Lower First Premolar

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 level)third ( 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 . .

Page 8: Lower First Premolar

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.

Page 9: Lower First Premolar

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.

Page 10: Lower First Premolar
Page 11: Lower First Premolar

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)

Page 12: Lower First Premolar

Lingual cusp is on a line with the buccal Lingual cusp is on a line with the buccal triangular ridge.triangular ridge.

The ML dev groove divides the lingual The ML dev groove divides the lingual cusp into 2 parts (lobes) smaller on the cusp into 2 parts (lobes) smaller on the mesial side , larger on the distal side.mesial side , larger on the distal side.

2 dev grooves on the M and D side making 2 dev grooves on the M and D side making the mesial and distal fossa ( no triangular the mesial and distal fossa ( no triangular fossa since the shape is not triangular)fossa since the shape is not triangular)

The CA and MRs are pronounced . the The CA and MRs are pronounced . the CA are broad.CA are broad.

Cervical portion of the crown is narrow Cervical portion of the crown is narrow and convex.and convex.

Page 13: Lower First Premolar

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.

Page 14: Lower First Premolar
Page 15: Lower First Premolar

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 The lingual outline (represented by the lingual cusp) is convex from the lingual cusp) is convex from the cervical line till the tip of the cusp.(the cervical line till the tip of the cusp.(the convexity is less than the buccal convexity is less than the buccal outline).outline).

The crest of curvature lingually The crest of curvature lingually approaches the mid third of the crown.approaches the mid third of the 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.

Page 16: Lower First Premolar

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.

Page 17: Lower First Premolar

The mesial surface of the crown is The mesial surface of the crown is smooth except for the mesiolingual dev smooth except for the mesiolingual dev groove,(MLDG).groove,(MLDG).

At the mesial CA , the surface is At the mesial CA , the surface is convex , below the CA , the surface is convex , below the CA , the surface is concave till the cervical line.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 the smooth till the mid third except for the presence of a deep DG.presence of a deep DG.

The root may be bifurcated in this The root may be bifurcated in this area. area.

Page 18: Lower First Premolar
Page 19: Lower First Premolar

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

Page 20: Lower First Premolar

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.

Page 21: Lower First Premolar
Page 22: Lower First Premolar

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

Page 23: Lower First Premolar

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.

Page 24: Lower First Premolar
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THANK YOUTHANK YOU