Permanent Mandibular Premolars Question And Answers

The Permanent Mandibular Premolars

Question 1. Describe in detail the morphology of the permanent mandibular 1″ premolar.
Answer:

Buccal aspect:

• The Crown appears symmetrical and roughly trapezoidal.
• The buccal surface is convex and smooth with no developmental grooves present.
• The slight curvature of the cervical line is seen.

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• The mesial and distal outlines along with the slopes are slightly concave.
• Developmental depression is seen between the 3 lobes.
• The buccal ridge is a continuous ridge extending from the cervical margin to the cusp tip.

Lingual aspect:

• The crown and root tapers lingually with the lingual cusp being smaller.
• The cervical portion is narrow and convex.
• The contact areas and marginal ridges are more pronounced.
• The lingual cusp is short and less developed.
• The mesial and distal occlusal fossae are seen on each side of the triangular ridge.
• The mesiolingual developmental groove is seen separating the mesiobuccal and lingual lobes.
• The root shows a smooth and convex narrow ridge, developmental depression with developmental groove mesially, and ends into a pointed apex.

Mesial aspect:

• The crown outline is roughly rhomboidal.
• The buccal cusp tip is nearly centered over a root.
• The buccal outline of the crown is prominently curved.
• The lingual outline of the crown is less convex.
• The distance from the cervical line lingually to the tip of the lingual cusp is about 2/3rd of the distance from the cervical line buccally to the tip of the buccal cusp.
• The mesiobuccal lobe is prominent.
• The lingual border of the mesial marginal ridge merges with the developmental depression mesiolingually and harbors the mesiolingual developmental groove.
• The cervical line is regular and curves occlusal.
• The root outline is tapered and ends in a pointed apex.
• The lingual outline is straight while the buccal outline is more curved.
• The mesial surface of the root is smooth and flat shallow grooves are present.

Distal aspect:

• The distal marginal ridge is higher above the cervix.
• There is no developmental groove on the distal marginal ridge.
• The surface is smoothly convex.
• The distal contact area is broader
• The cervical line has less curvature.
• The root surface is more convex.
• A shallow development depression is present.

Occlusal aspect:

• It is roughly diamond-shaped.
• The buccal ridge and the mesiobuccal and distobuccal line angles are prominent.
• The marginal ridges are well-developed.
• The lingual cusp is small
• The surface shows a heavy buccal triangular ridge and a small lingual triangular ridge.

Fossae:

• Mesial and distal fossae correspond in location to the mesial and distal triangular fossae.
• The mesial fossa is more linear.
• The distal fossa is more circular and is circumscribed by the distobuccal cusp ridge, the distal marginal ridge, the buccal triangular ridge, and the distolingual cusp ridge.

Developmental groove:

• The mesial developmental groove extends buccolingually.
• Over the mesiolingual surface, it becomes mesiolingual developmental groove.
• Distal developmental groove. It is crescent-shaped.
• It contains a distal developmental pit with accessory supplemental grooves.

Measurements:

• Cervico-occlusal crown length – 8.5 mm
• Root length – 14 mm
• Mesiodistal crown diameter -7 mm
• Mesiodistal crown diameter at cervix – 5 mm
• Bucco-lingual crown diameter -7.5 mm
• Bucco-lingual crown diameter at cervix -6.5 mm
• Curvature of cervical line – mesial – 1 mm
• The curvature of the cervical line, – distal – 0 mm

Question 2. Describe in detail the morphology of the permanent mandibular 2nd premolar.
Answer:

Buccal aspect:

• It shows a shorter buccal cusp.
• Mesiobuccal and distobuccal cusp ridges show less angulation.
• The contact areas are broad.
• The root is broader with a blunt apex.

Lingual aspect:

• The lingual lobes are well-developed. Loss of the occlusal surface is seen.
• Longer and larger mesiobuccal cusp and distolingual cusps are seen.
• A groove is present between them
• The surface is smooth and spheroidal.
• The root is wide lingually.
• Less mesial and distal sides are seen.
• The root surface is smoothly convex.

Mesial aspect:

• The crown and root are wider buccolingually.
• The buccal cusp is shorter.
• The lingual lobe is greater.
• The marginal ridge is at right angles to the long axis.

Distal aspect:

• The more occlusal surface is seen.
• The distal marginal ridge is at a lower level.
• The crown is tipped distally.

Occlusal aspects:

• The three-cusp type appears square lingual to the buccal cusp ridges when highly developed.
• The three cusps that are distinct are the largest buccal cusp, next mesiolingual cusp and the distolingual cusp is the smallest.
• The two cusps type appears round lingual to the buccal cusp ridges.
• Each cusp has well-formed triangular ridges.

Central pit:

Location:

• Midway between the buccal cusp ridge and the lingual margin of the occlusal surface.
• Slightly distal to the central point between mesial and distal marginal ridges.

Fossa:

• Mesial triangular fossa – distal to mesial marginal ridge.
• Distal triangular fossa-mesial to the distal marginal ridge.

Developmental groove:

• The mesial developmental groove travels in a mesiobuccal direction and ends in a mesial triangular fossa.
• The distal developmental groove travels in a distobuccal direction and ends in a distal triangular fossa.
• Lingual developmental groove extends lingually between the two lingual cusps and ends on the lingual surface of the crown.
• Supplemental grooves and depression are often seen radiating from the developmental grooves.

Two cusps type:

• It travels in a mesiodistal direction.
• It is most often crescent-shaped.
• It terminates in mesial and distal fossae.
• Central developmental groove:
• It travels in a mesiodistal direction.
• It is most often crescent-shaped.
• It terminates in mesial and distal fossae.
• Mandibular left second premolar, buccal aspect. (Grid 1 SQuestion mm)
• Mandibular left second premolar, lingual aspect. (Grid 1 SQuestion mm)
• Mandibular left second premolar, mesial aspect. (Grid 1 SQuestion mm)

Measurements:

• Cervico-occlusal crown length – 8 mm
• Root length – 14.5 mm
• Mesiodistal crown diameter -7 mm
• Mesiodidstal crown diameter at cervix – 5mm
• Buccolingual crown diameter – 8 mm
• Bucco-lingual crown diameter at cervix -7mm
• The curvature of cervical line – mesial
• The curvature of the cervical line – distal – 0 mm
• Mandibular left second premolar, distal aspect.

Question 3. Differentiate between permanent mandibular 1st premolar and 2nd premolar.
Answer:

Question 4. Chronology of mandibular 1st and 2nd premolar.
Answer: