Lower 4

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Lower 4

  1. 1. POSITION : The mandibula r first premolar is situated between the canine and second premolar
  2. 2. CHARACTERISTICS : Resemble those of the mandibular canine : 1. The buccal cusp is long & sharp. 2. The MB cusp ridge is shorter than the DB cusp ridge. 3. The BL measurement is similar to that of the canine. 4. The occlusal surface slopes sharply lingually in a cervical direction. 5. The outline form of the occlusal aspect resembles the outline form of the incisal aspect of the canine. Resemble those of the second mandibular premolar: 1. Except for the longer cusp, the outline of crown & root from the B aspect resembling the second premolar. 2. The contact areas , M&D ,are nearly at the same level. 3. The curvatures of the cervical line , M&D ,are similar. 4. It has more than one cusp. 5. The root length is similar to that of the second premolar
  3. 3. BUCCAL ASPECT: Mesial contact Trapezoidal with the area located D contact shorter of the the cervical to uneven area is sides at the cervix junction of the almost at occlusal & the same M outline is third middle level D outline is straight or slightly concave sligthly concave D Root is cone shape Shallow D developmental depression B ridge is prominent M slope is shorter than D slope B cusp is The B surface pointed is more convex & large the than The maxillary cervical premolars line is convex root Shallow M M wise developmen tal depression
  4. 4. LINGUAL ASPECT: L cusp is short, small &less developed M The cervical portion of the crown lingually is narrow &convex,with concavities between the cervical line & contact areas Crown & root taper markedly toward the lingual D fossa M fossa Contact areas & marginal ridges are pronounced ML developmenta Pointed l groove apex The root is much narrower on the L side forming a smooth narrow ridge L cusp tip is pointed D
  5. 5. The crown B MESIAL ASPECT: cusp tip isis outline B outline is convex B B cusp is much higher than the lingual cusp nearly centered roughly over the root ,or rhomboidal it may be buccal to the center Crown surface is convex at the M contact The crown L outline is area appears less convex overhanging Then it becomes than the The B ML root in a the sharply concave groovelingual of extent between this area concavity direction & cervical line The Crest of is 1 mm curvature or even cervical near the Deep line is less slightly middle developmental concave third groove root wise The differenc L cusp is e in in line height is with the about 1/3 lingual of the border of crown the root length L Crest of curvature is lingual to the lingual out line of the root
  6. 6. DISTAL ASPECT: D marginal ridge is more coronal & horizontal than the M It is confluent with the L cusp ridge L D contact area is broader B The cervical line is almost straight The root surface distally is more convex Shallow developmental depression
  7. 7. OCCLUSAL ASPECT: The middle B lobe forming the B cusp makes up the major bulk of the the tooth B B ridge is prominen t heavy B triangular ridge M M dg Roughly ML diamond dg shape Dd pit DB & MB line angles are prominent & M triangular D dg is round fossa crescent Is linear in form shape L cusp is small L D D triangul ar fossa is more circular Small L triangular ridge
  8. 8. Dina Khaled Mohamed Refaat

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