MANDIBULAR PREMOLARS

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.

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

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

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.

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

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

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.

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.

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

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.

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

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

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.

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

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. 

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

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.

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.

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.  

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

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

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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