Oral Anatomy 3b - The Mandibular First Permanent Molar
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How does the mandibular first permanent molar appear when viewed occlusally?
- The crown of this tooth, when viewed occlusally, is somewhat pentagonal in outline.
- It is broader mesiodistally than buccolingually.
- The occlusal surface is divided into buccal and lingual parts by a mesiodistal occlusal fissure, which arises from a deep central fossa.
- The buccal side of the occlusal table has three distinct cusps: mesiobuccal, distobuccal, and distal.
- Each cusp is separated by a groove, which joins the mesiodistal fissure.
- On the lingual side there are two cusps: mesiolingual and distolingual.
- The fissure separating the lingual cusps joins the mesiodistal fissure in the region of the central fossa.
- The lingual cusps tend to be larger and more pointed, though they are not disproportionately larger than the mesiobuccal and distobuccal cusps.
- The tips of the buccal cusps are displaced lingually, are rounded and are lower than the lingual cusps.
- The smallest cusp is the distal cusp, which is displaced slightly towards the buccal surface.
- In 90% of cases, the mesiolingual cusp is joined to the distobuccal cusp across the floor of the central fossa.
- This feature and the five-cusped pattern is termed the dryopithecus pattern. (Y5 pattern)
How does the mandibular first permanent molar appear from the buccal aspect?
- From the buccal aspect, three cusps are seen, the distal cusp being the smallest.
- The fissure separating the mesiobuccal and distobuccal cusps arises from the central fossa on the occlusal surface and terminates halfway up the buccal surface in a buccal pit.
- The buccal surface appears markedly convex, especially at the cervical third of the crown.
- This convexity is associated with the characteristic lingual inclination of the buccal cusps.
How does the mandibular first permanent molar appear from the lingual aspect?
- From the lingual aspect, although the two lingual cusps are nearly equal in size, the mesiolingual cusp appears slightly larger.
- The fissure between the lingual cusps arises from the central fossa on the occlusal surface but does not extend a significant way down the lingual surface.
- The lingual surface is convex in its occlusal and middle thirds but is flat or concave cervically.
- Part of the buccal profiles and proximal surfaces may be seen.
How does the mandibular first permanent molar appear from the mesial aspect?
- Viewed mesially, the mesial marginal ridge joining the mesiobuccal and mesiolingual cusps is V-shaped, being notched at its midpoint.
- the mesial surface is flat or concave cervically and convex in its middle and occlusal thirds.
How does the mandibular first permanent molar appear from the distal aspect?
- From the distal aspect the distal marginal ridge joining the distal and distolingual cusps also appears V-shaped.
- The cervical third of the distal surface is relatively flat, the middle and occlusal thirds highly convex.
- Thus, the distal surface is more convex than the mesial surface due to the distal cusp.
- The proximal views of the illustration highlight the highly convex slope of the buccal surface compared to the lingual surface.
What is the cervical
margin and the root like for the mandibular first permanent molar?
- The cervical margin follows a uniform contour around the
- The two roots, one mesial and one distal, arise from a
- common root stalk.
- They are both markedly flattened mesiodistally, and the
- mesial root is usually deeply grooved.
- Both roots curve distally.
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