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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)
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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.
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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.
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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.
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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.
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What is the cervical
margin and the root like for the mandibular first permanent molar?
- The cervical margin follows a uniform contour around the
- tooth.
- 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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