Crown Size and Shape of Mandibular Premolars
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Questions and Answers

What is unique about the mandibular first premolar's mesial marginal ridge?

  • It is more cervically located than the distal marginal ridge (correct)
  • It is more apically located than the distal marginal ridge
  • It is more apically located than the lingual cusp
  • It is more cervically located than the lingual cusp

    • What is the shape of the mandibular first premolar when viewed proximally?

  • Oval
  • Rhomboid (correct)
  • Triangular
  • Circular

    • How does the lingual cusp of the mandibular first premolar compare to the buccal cusp?

  • It is equally as long as the buccal cusp
  • It is only slightly shorter than the buccal cusp
  • It is more than one third shorter than the buccal cusp (correct)
  • It is longer than the buccal cusp

    • What can be seen from the lingual aspect of the mandibular first premolar?

    <p>Much of the occlusal surface</p> Signup and view all the answers

    How does the crown of the mandibular first premolar tilt?

    <p>Towards the lingual surface at the cervix</p> Signup and view all the answers

    What is the shape of the root of the mandibular first premolar?

    <p>Tapered from the cervical line to a pointed apex</p> Signup and view all the answers

    Which groove may appear to be continuous with the mesial groove in mandibular premolars?

    <p>Mesiolingual groove</p> Signup and view all the answers

    What is a characteristic of the occlusal surface of the mandibular first premolar?

    <p>It slopes sharply lingually in a cervical direction.</p> Signup and view all the answers

    What is a characteristic of the buccal cusp of the mandibular first premolar?

    <p>It is long and sharp.</p> Signup and view all the answers

    Which of the following is a characteristic of the mandibular first premolar that is similar to the mandibular canine?

    <p>The buccolingual measurement is similar.</p> Signup and view all the answers

    What is a characteristic of the root of the mandibular first premolar compared to the second premolar?

    <p>It is shorter than the second premolar root.</p> Signup and view all the answers

    Which of the following is a characteristic of the mandibular first premolar that is similar to the second premolar?

    <p>The outline of the crown and root from the buccal aspect.</p> Signup and view all the answers

    What is the shape of the mandibular first premolar from the buccal view?

    <p>Roughly a five-sided pentagon</p> Signup and view all the answers

    What is the characteristic of the mesial cusp ridge on mandibular first premolars?

    <p>Mesial cusp ridge is shorter than the distal cusp ridge</p> Signup and view all the answers

    Where is the mesial contact located on mandibular first premolars?

    <p>At the junction of the occlusal and middle thirds</p> Signup and view all the answers

    What is the purpose of the vertical depressions on the occlusal third on either side of the buccal ridge?

    <p>To serve as spillways for food during mastication</p> Signup and view all the answers

    What is the characteristic of the roots of mandibular first premolars?

    <p>They are slightly thicker and shorter than the roots of the second premolar</p> Signup and view all the answers

    What is the characteristic of the crown on the lingual half of mandibular first premolars?

    <p>It is narrower mesiodistally than on the buccal half</p> Signup and view all the answers

    What is the direction of the slope of the mesial marginal ridge of the mandibular first premolar?

    <p>Cervically from the buccal towards the center of the occlusal surface</p> Signup and view all the answers

    What is the position of the distal marginal ridge of the mandibular first premolar compared to the mesial marginal ridge?

    <p>More horizontal and more occlusal</p> Signup and view all the answers

    What is the orientation of the triangular ridge of the lingual cusp of the mandibular first premolar?

    <p>Nearly horizontal</p> Signup and view all the answers

    What is the location of the buccal height of contour of the crown of the mandibular first premolar?

    <p>Just occlusal to the cervical line</p> Signup and view all the answers

    What is the shape of the buccal crown outline of the mandibular first premolar?

    <p>Convex</p> Signup and view all the answers

    What is the location of the height of contour of the lingual surface of the crown of the mandibular first premolar?

    <p>At the center of the total crown length</p> Signup and view all the answers

    What is the characteristic of the cervical line on the proximal surfaces of all premolars?

    <p>It is more prominent on the mesial surface</p> Signup and view all the answers

    What is the characteristic of the roots of mandibular first premolars?

    <p>They taper apically</p> Signup and view all the answers

    What is a characteristic of the outline of the crown of a mandibular first premolar?

    <p>It is not symmetrical and has more bulk in the distal half</p> Signup and view all the answers

    What is a distinctive feature of the mesiolingual portion of the crown outline of a mandibular first premolar?

    <p>It is pushed in and appears diamond-shaped</p> Signup and view all the answers

    How do the distal marginal ridge and the distal cusp ridge of the buccal cusp of a mandibular first premolar relate to each other?

    <p>They form a right angle</p> Signup and view all the answers

    How do the mesial and distal cusp ridges of the buccal cusp of a mandibular first premolar relate to each other?

    <p>They are nearly aligned in a straight line mesiodistally</p> Signup and view all the answers

    Where are the contact areas of a mandibular first premolar located, from the occlusal view?

    <p>At the point of broadest mesiodistal dimension, just lingual to the line of the buccal cusp ridges</p> Signup and view all the answers

    What is the characteristic of the buccal crest of contour of a mandibular first premolar?

    <p>It is slightly mesial to center</p> Signup and view all the answers

    What is the characteristic of the triangular ridge of the buccal cusp of a mandibular first premolar?

    <p>It is long and slopes lingually</p> Signup and view all the answers

    What is the characteristic of the transverse ridge of a mandibular first premolar?

    <p>It is prominent and completely separates the mesial and distal fossae</p> Signup and view all the answers

    Study Notes

    Crown Size and Shape of Mandibular Premolars from the Buccal Aspect

    • The crown of the mandibular first premolar is roughly a five-sided pentagon in shape from the buccal view.
    • The crown has bilateral symmetrical shape, except for the shorter mesial than distal cusp ridge and a greater distal bulge of the crown.
    • The buccal cusp is relatively sharp (110°) and has a central ridge extended from the cusp tip to the cervical line, called the buccal cusp ridge.
    • Mesial cusp ridge notch is more common, and the mesial contact is near the junction of the occlusal and middle thirds.
    • The distal contact area is slightly more occlusal in position than the mesial contact.

    The Lingual Aspect

    • The crown is much narrower mesiodistally on the lingual half than on the buccal half.
    • The lingual cusp is quite small and short, and is often pointed at the tip.
    • Much of the occlusal surface of the tooth can be seen from the lingual aspect because of the shortness of the lingual cusp.
    • The mesial marginal ridge is more cervically located than the distal marginal ridge.
    • The mesiolingual developmental groove separated the mesial marginal ridge from the lingual cusp.

    The Proximal View

    • The mandibular first premolar has a rhomboid shape from this aspect.
    • The crowns of the mandibular first premolars tilt noticeably toward the lingual surface at the cervix.
    • The tip of the buccal cusp is on a line with the long axis of the root and the apex of the root.
    • The lingual cusp is considerably shorter than the buccal cusp by more than one-third of the total crown length.
    • The tip of the lingual cusp is on a line with the lingual outline of the root.

    The Occlusal View

    • Much of the buccal surface is visible from this view since the tip of the buccal cusp is slightly buccal to the tooth center.
    • The outline of the crown is usually not symmetrical (more bulk in the distal half).
    • The mesiolingual portion of the crown outline has been pushed in (identifying feature).
    • The outline converges toward the lingual, especially on the mesial.
    • The distal marginal ridge forms close to a right angle with the distal cusp ridge of the buccal cusp.
    • The mesial and distal cusp ridges of the buccal cusp on the mandibular first premolars are nearly aligned in a straight line mesiodistally.

    Occlusal Morphology of Mandibular Premolars from the Occlusal View

    • The triangular ridge of the buccal cusp is long and slopes lingually from the cusp tip to where it joins the very short triangular ridge of the lingual cusp.
    • The mesial fossa is more linear buccolingually, but the distal fossa is more frequently larger and deeper.
    • Each fossa has a pit.
    • Only rarely is the pronounced transverse ridge of the mandibular first premolar crossed by a fissured central groove.
    • More commonly, there are mesial and distal developmental grooves running in a nearly buccolingual direction, flaring buccally from the mesial and distal fossae.

    Characteristics Resembling Mandibular Canine and Second Premolar

    • The buccal cusp is long and sharp, and is the only occluding cusp.
    • The buccolingual measurement is similar to that of the canine.
    • The occlusal surface slopes sharply lingually in a cervical direction.
    • The mesiobuccal cusp ridge is shorter than the distobuccal cusp ridge.
    • The outline form of the occlusal aspect resembles the outline form of the incisal aspect of the canine.
    • The outline of the crown and root from the buccal aspect resembles that of the second premolar.
    • The contact areas, mesially and distally, are near the same level.
    • The curvatures of the cervical line mesially and distally are similar.
    • The tooth has more than one cusp.
    • The root of the mandibular first premolar is shorter generally than that of the mandibular second premolar, but is closer to the length of the second premolar root than it is to that of the mandibular canine.

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    Description

    This quiz covers the characteristics of the mandibular first premolar from the buccal view, including its shape, size, and cusp ridges. It also discusses the differences between the mesial and distal cusps.

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