1. MANDIBULAR PREMOLARS

2. INTRODUCTION
Mandibular premolars are four in number, two first premolars and two second premolars located one on each side of the dental arch.
They are successors of mandibular deciduous molars.
The functions include mastication and maintenance of vertical dimension of face.
Also assists canines to shearing the teeth and support the side of mouth and cheeks.

3. Mandibular First premolar
Mandibular first premolar is located between canine and second premolar and therefore bears resemblance to both, in certain features

4. BUCCAL ASPECT
Crown
Shape – tooth is bilaterally symmetrical has trapezoidal shape with narrow cervix.
Mesial outline is straight or slightly convex from cervix to contact area.
Contact area is located slightly occlusal to midpoint of the tooth.
Distal outline is more convex and contact area is nearly at the same level as mesial or slightly more occlusal
Cervical line is slightly curved towards the root

5. Occlusal outline is represented by buccal cusp and cusp slopes.
Buccal cusp is long and sharp and the cusp tip is located slightly mesial to the center.
Mesial cusp ridge is shorter than the distal cusp ridge.
Ridges meet at an obtuse angle making the cusp less sharp.

6. Buccal surface is convex with a well developed buccal ridge extending vertically from cervical region to the cusp tip
On either side of buccal ridge shallow depressions may be present.
Root – Mandibular first premolar has only one root.
Root is conical and tapers to a nearly pointed apex

7. Distal curvature of apical 3rd of root
MANDIBULAR 1st PREMOLAR-BUCCAL ASPECT
Distal cusp ridge
Mesial cusp ridge
Buccal ridge
Distal curvature of apical 3rd of root

8. LINGUAL ASPECT From this aspect mandibular premolars show many unique characteristics.
1. Crown and root taper considerably to the lingual side
2. Occlusal aspect slopes lingually in a cervical direction
3. Contact areas and marginal ridges are more prominent because of narrow cervical region.
4. Lingual cusp is short and poorly developed but is pointed.
This cusp is a non occluding cusp.

9. Both mesial and distal marginal ridge can be seen.
Mesial marginal ridge is sloping and more cervically placed.
While distal marginal ridge is relatively straighter and more occlusally placed.
Mesio-lingual developmental groove which extends to lingual surface along the mesio-lingual line angle, demarcating the mesial marginal ridge from mesial slope of lingual cusp.

10. MANDIBULAR 1st PREMOLAR-LINGUAL ASPECT
Buccal triangular ridge
Small rudimentary lingual cusp
Mesiolingual developmental groove

11. MESIAL ASPECT
Crown
Shape- Crown is rhomboidal in shape with noticeable tilt to the lingual side at the cervix.
The buccal outline is curved from cervical line to the buccal cusp tip.
A distinct inclination to lingual side is observed with crest of curvature located at the junction of middle and cervical 1/3rd.

12. Lingual outline is less curved than buccal and crest of curvature is located nearly at middle 1/3rd.
Because of extreme lingual tilting lingual out line extend beyond the boundary of root outline giving an impression lingual side is overhanging
Cervical line is curved and semicircular

13. Occlusal outline is represented by buccal and lingual cusps and mesial marginal ridge.
The inclination of the occlusal aspect can be well appreciated from mesial aspect and the lingual height of the tooth is only 2/3rd of buccal height
Lingual cusp is short but sharp and is non functional.
Lingual cusp tip is in line with lingual root outline

14. The mesial marginal ridge is at a lower level compared to distal so, more of occlusal surface can be seen from this aspect.
Mesial surface is smooth.
A prominent mesio-lingual developmental groove can be visible
Root is nearly straight at cervical 1/3rd and taper at apical 1/3rd to a blunt apex.
A deep developmental groove may be present on root.

15. MESIAL ASPECT Lingually sloping occlusal surface
Lingual cusp
Lingually sloping occlusal surface
Mesiolingual developmental groove

16. DISTAL ASPECT
Mandibular first premolar shows various differences from mesial aspect.
1. Distal marginal ridge is longer and is more occlusal than that of mesial marginal ridge.
2. Distal marginal ridge is horizontal; nearly perpendicular to long axis of tooth; in contrast to mesial marginal ridge which shows a lingual inclination.
3. No evidence of developmental groove on the distal aspect of crown.
4. Root is more convex on distal aspect. 

17. MANDIBULAR 1st PREMOLAR-DISTAL ASPECT
Buccal cusp
Lingual cusp
Distal marginal ridge(relatively horizontal and devoid of developmental groove)

18. OCCLUSAL ASPECT The occlusal aspect is roughly diamond shaped.
Tooth is not bilaterally symmetrical.
The distal portion appears bulkier than mesial.
Considerable degree of lingual convergence of the tooth can be appreciated from this aspect
Occlusal aspect is broadest at the buccal half, in the region of contact
Occlusal surface shows anatomic landmarks such as cusps, ridges, grooves, fossa etc.

19. CUSPS Occlusal surface of mandibular first premolar shows two cusps.
Buccal cusp and its triangular ridge make up the bulk of the occlusal surface of the tooth.
Lingual cusp is small, sharp and is nonfunctional.
Tip is at considerably lower level than buccal cusp.

20. RIDGES Triangular ridges of both buccal and lingual cusp can be seen.
Buccal triangular ridge occupies the major portion of occlusal aspect which also shows a lingual inclination.
The triangular ridge of buccal cusp forms a transverse ridge with the small triangular ridge of lingual cusp.
Marginal ridges are well developed and prominent.  

21. FOSSA AND PITS
Occlusal surface of mandibular first premolar shows two minor fossae, which are located on either side of the transverse ridge namely mesial and distal fossae.
Mesial fossa is linear and shallow
Distal fossa is circular and deeper
Pits may be seen in fossae

22. GROOVES
A shallow central groove may be found extending from mesial to distal fossa across the transverse ridge.
The central groove divides the occlusal surface in to two unequal parts.
Mesial and distal developmental grooves are found around the fossae

23. MANDIBULAR 1st PREMOLAR-OCCLUSAL ASPECT
Mesiobuccal cusp ridge
Buccal cusp
Distobuccal cusp ridge
Buccal triangular ridge
Mesial fossa
Distal fossa
Distal marginal ridge
Mesial marginal ridge
Lingual cusp
Mesiolingual developmental groove

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