The Permanent Mandibular Molars
The permanent mandibular molars are the largest teeth in the lower jaw. There are three mandibular molars in each quadrant, namely the first, second and third. They vary in dimension, number of cusps and occlusal outline but resemble each other in form.
Table of Contents
- The mandibular molars generally have two roots.
- The crown is wider mesiodistally than buccolingually by about 1 mm, whereas the crown of the maxillary molar is wider buccolingually than mesiodistally.
- The crowns of the mandibular molars are shorter cervico occlusally than the mandibular anteriors and premolars but are wider mesiodistally and Labiolingually.
- The roots are shorter than the other mandibular teeth.
Read And Learn More: Oral Anatomy Notes
- The combined mesiodistal width of the mandibular molar teeth is equal to or greater than that of the teeth present anterior to them up to the midline.
- The mandibular molars are the strongest teeth in the mandible due to the bulk and anchorage.
- They help in mastication and comminution of food. The morphology of this tooth will be described from the buccal, lingual, mesial, distal and occlusal aspects.
- The nomenclature, chronology and measurement of the mandibular first molar are given in tables.
Nomenclature: Mandibular first molar:
Mandibular first molar: Chronology and measurements:
The Permanent Mandibular First Molar
The mandibular molar has five well-developed cusps which include two buccal, i.e. The mesiobuccal and distobuccal, two lingual cusps i.e mesiolingual and distolingual cusp and one distal cusp and two well-developed roots, mesial and distal.
Buccal aspect:
Features of the crown:
Two buccal cusps, buccal part of the distal cusp and cusp tips of the lingual cusp (as the lingual cusps are placed higher), are visible when the tooth is held vertically.
Shape and surface:
- The shape is roughly trapezoidal.
- The surface of the cusps are convex except for the developmental groove that separates the buccal cusps.
- At the point of termination of the developmental grooves, a developmental depression runs mesiodistally above the cervical ridge that leads to the concavity.
- This concavity is continuous with the one on the root.
- The mesiobuccal developmental groove is present between the mesiobuccal and distobuccal cusp and the distobuccal developmental groove between the distobuccal and distal cusp.
- The mesiobuccal developmental groove is located mesial to the bifurcation of the root and terminates in the middle third of the crown.
- The distobuccal developmental groove is parallel to the long axis of the distal root and terminates near the distobuccal line angle in the cervical third of the crown.
Mesial outline:
- The mesial outline is concave in the cervical third and then convex From the contact area to the cusp ridge.
- The mesial contact area is located at the junction of the middle and Occlusal third.
Distal outline:
- The distal outline is straight from the cervical line and then convex From the distal contact area to the cups ridge.
- The distal contact area is located at the middle of the middle third.
Occlusal outline:
- The buccal cusps are flat due to lesser curvature of the cusp ridges.
- The mesiobuccal cusp is the widest. The distobuccal cusp is approximately of the same width as the mesiobuccal cusp. These two buccal cusps occupy most of the buccal surface.
- The distal cusp is the smallest among the buccal cusps and occupies a Small part of the buccal and major part of the distal portion of the crown. It is sharper than the two buccal cusps.
Features of the root:
- There are two roots, the mesial and distal roots, and are well developed.
- The bifurcation of the roots is approximately 3 mm from the cervical line.
- Mesial root:
- The mesial root curves mesially from the cervical third to the middle Third and then curves distally till the apex located below the Mesiobuccal cusp tip.
- Distal root:
- The distal root is less curved than the mesial root with its axis distally tilted.
- The apex in line with or distal to the distal contact area. It is more Pointed than the mesial root.
- The developmental depressions on the sides of the root help in secure and better anchorage of the tooth.
Lingual aspect:
Features of the crown:
The two lingual cusps and the lingual part of the distal cusp are seen from this aspect.
Shape and surface:
- Lingual convergence is seen in the crown with the distal part exhibiting More convergence and thus part of the mesial and distal surfaces is Seen. The crown also converges cervically.
- The surface is convex in the occlusal third, concave in the middle third And flat near to the cervical line.
- The lingual developmental groove separates the two lingual cusps and Is line with the bifurcation of the root and runs a short distance on the lingual surface.
Mesial outline:
- The mesial outline is convex from the cervical line to the marginal ridge.
Distal outline:
- The distal outline is straight from the cervical line to below the distal contact area.
Occlusal outline:
- The lingual cusps are sharp. The mesiolingual cusp is the widest; the Distolingual cusp might be as wide. The cuspal slopes of the two lingual cusps meet at an obtuse angle of about 100°.
Features of the root:
- The bifurcation of the root is approximately 4 mm below the cervical line. A developmental depression is seen extending from the bifurcation and fading away below the cervical line.
- The roots are 1 mm longer than buccally, but this is due to the cervical line being at a higher level.
- They are mesiodistally narrower than buccally.
Mesial aspect:
On holding the tooth perpendicular to the line of vision, the mesiobuccal and mesiolingual cusps and the mesial root are seen.
Features of the crown:
Shape and surface:
- The buccolingual dimension is greater mesially than distally.
- As the mesial part of the tooth is broader and the mesial cusps are Placed at a higher level the distal aspect of the tooth is not visible.
- The crown is roughly rhomboidal with a lingual tilt to the axis.
- The surface is concave from the cervical line to the mesial contact area; it is convex from the mesial contact area to the occlusal third.
- The mesial contact area in the centre of the crown is buccolingually.
Buccal outline:
- The buccal outline is convex from the cervical line in the area of the Buccal cervical ridge and less convex or may be flat-concave in the occlusal third.
Lingual outline:
- The lingual outline is straight from the cervical third to the middle Third and then convex till the tip of the mesiolingual cusp.
Occlusal outline:
- The mesiolingual cusp is placed higher than the mesiobuccal cusp.
- The mesial marginal ridge is 1 mm below the cup tips and continuous With the slopes of the mesiobuccal and mesiolingual cusps.
Cervical line:
The cervical line is irregular and curves occlusally in the centre of the mesial surface.
Features of the root:
- The mesial root is the only root visible.
- The buccal outline of the mesial root is straight from the cervical third to the middle third and curves lingually to the apex which is below the mesiobuccal cusp.
- The lingual outline is slanted in a buccal direction.
- No developmental depressions are seen.
Distal aspect:
Features of the crown:
Surface:
- The distal surface is convex over the two cusps, the distolingual and The distal cusp.
- The distobuccal developmental groove forms a concavity at the cervical Part of the distobuccal line angle.
The distal aspect is similar to the mesial aspect except for the following variations:
- More of the buccal and lingual surface is seen as the crown converges distally from the mesial aspect; the convergence is more on the buccal surface than the lingual surface.
- Most of the occlusal surface is seen. This is because
- The crown is distally inclined on the root axes and
- The distal marginal ridge dips in a cervical direction
- The distal cusp is buccal to the centre of the crown buccolingually.
- The distal contact area is in line with the centre of the distal root thus buccal to the centre of the distal marginal ridge.
- The cervical line is irregular and may dip towards the root.
- The crown might extend beyond the confines of the root trunk.
- The lingual border of the mesial root might be visible.
Occlusal aspect:
- Outline: Hexagonal
- Dimensions:
-
- The crown is wider mesiodistally than buccolingually by 1 mm.
- The crown is wider mesially than distally.
- The dimension between the mesial and distal contact areas buccally is Greater than the mesiodistal measurement of the two lingual cusps.
The triangular ridge of the lingual cusps is longer than that of the buccal cusps as the central groove is in the centre buccolingually. The rest of the occlusal surface is described in table.
Occlusal surface of the mandibular first molar:
The features that can help in the identification of the mandibular first molar are given in the box.
Features to identify the mandibular first molar:
Hexagonal occlusal outline
- Five cusps
- Two roots – mesial and distal
Differentiation Between The Right And Left Mandibular First Molar
- The distal cusp is the smallest cusp
- The mesial side is wider than the distal side
- The mesiodistal dimension is greater than the buccolingual dimension
Development And Landmarks Crown And Root Of The Mandibular First Molar
The Permanent Mandibular Molars Synopsis
Buccal aspect:
Crown:
- The two buccal cusps, the buccal part of the distal cusp, cusp tips of the lingual cusp are visible when the tooth is held vertically.
- The shape is roughly quadrilateral.
- The mesiobuccal developmental groove is present between the mesiobuccal and distobuccal cusp and the distobuccal developmental groove between the Distobuccal and distal cusp.
- The mesial contact area is located at the junction of the middle and occlusal third.
- The distal contact area is located in the middle of the middle third.
- The mesiodistal cusp is the widest and may have some curvature. The distal cusp is the smallest among the buccal cusps occupies.
Root:
- There are two roots, the mesial and distal roots and are well-developed.
Lingual aspect:
- The two lingual cusps and the lingual part of the distal cusp are seen from this aspect.
- The surface is convex in the occlusal third, concave in the middle third and flat near to the cervical line.
- The lingual cusps are sharp. The mesiolingual cusp is the widest; the distolingual cusp might be as wide. The cuspal slopes of the two lingual cusps meet at an obtuse angle of about 100°.
Root:
- The roots are 1 mm longer than buccally, but this is due to the cervical line being at a higher level. They are mesiodistally narrower than buccally.
Mesial aspect:
On holding the tooth perpendicular to the line of vision the mesiobuccal and mesiolingual cusp and the mesial root are seen.
Crown:
- The buccolingual dimension is greater mesially than distally.
- The crown is roughly rhomboidal with a lingual tilt to the axis.
- The surface is concave from the cervical line to the mesial contact area; it is convex from the mesial contact area to the occlusal third.
- The mesial contact area in the centre of the crown is buccolingual.
- The mesiolingual cusp is placed higher than the mesiobuccal cusp.
- The mesial marginal ridge is 1 mm below the cup tips and continuous with the slopes of the mesiobuccal and mesiolingual cusps.
Root:
- The mesial root is the only root visible.
Distal aspect:
Crown:
- The distal surface is convex over the two cusps, the distolingual and the distal cusp.
- The distal aspect is similar to the mesial except for a few variations: More of the buccal and lingual surface is seen as the crown.
- Most of the occlusal surface is seen as the crown is distally inclined on the root axes.
Occlusal aspect:
- Outline is hexagonal.
- The crown is wider mesiodistally than buccolingually by 1 mm.
- The crown is wider mesially than distally.
- The dimension between the mesial and distal contact areas buccally is greater than the mesiodistal measurement of the two lingual cusps.
- In decreasing order of size, the cusps are as follows – mesiobuccal, mesiolingual, distolingual, distobuccal and distal.
- The central fossa is located between the buccal and lingual cusp ridges.
- The mesial and distal triangular fossa are the minor fossa.
- The transverse ridge is formed by the union of the triangular ridge of the mesiobuccal cusp and the mesial part of the triangular ridge of the mesiolingual cusp.
- The central groove has a zig-zag pattern.
The Permanent Mandibular Second Molar
The permanent mandibular second molar is distal to the first molar, and these are two in number, i.e. One in each quadrant. It supplements the first molar in function.
The second molar has four cusps, the mesiobuccal, mesiolingual, distobuccal and distolingual cusps. The fifth cusp is absent. There are two roots: Mesial and distal.
The mandibular second molar resembles the first molar with a few variations. The morphology of this tooth will be described from the buccal, lingual, mesial, distal and occlusal aspects. The nomenclature, chronology and measurement of the mandibular second molar are given in tables.
Nomenclature: Mandibular second molar:
Mandibular second molar: Chronology and measurements:
Buccal aspect:
The two buccal cusps and part of the lingual cusps might be seen from this aspect.
Features of the crown:
Shape and surface:
- The crown is shorter cervico-occlusally and narrower mesiodistally Than the first molar.
- The buccal surface contains one groove, the buccal developmental Groove that separates the mesiobuccal and the distobuccal cusps and Terminates at the middle third of the buccal surface.
- The surface is smooth.
- The buccal cervical ridge is not as prominent as in the first molar.
Mesial outline:
- The mesial outline is straight from the cervical line and then convex.
- The mesial contact area is located at the junction of the middle and the Occlusal third.
Distal outline:
- The distal outline is more convex than the mesial outline.
- The distal contact area is located at the middle of the middle third.
Occlusal outline:
- There are two buccal cusps namely the mesiobuccal and the distobuccal cusps which are separated by the buccal developmental groove.
- The cusp ridges are flatter than in the first molar.
Cervical line:
The cervical line is straight or curved towards the bifurcation of the Root.
Features of the root:
- There are two roots – mesial and distal.
- The roots is shorter than in the first molar.
- The axes of the roots are nearly parallel with the roots being close to each other.
- The roots are distally tilted.
- The roots are sometimes fused.
Lingual outline:
Features of the crown:
- The mesial and distal outline is similar to that on the labial aspect.
- The lingual convergence is lesser than in the first molar and thus lesser portion of the mesial and the distal surfaces is seen.
Occlusal outline:
- The mesiolingual and the distolingual cusps are seen separated by the Lingual developmental groove.
- The lingual cusps are placed higher than the buccal cusps.
- The two lingual cusps are of the same size and sharper than the buccal Cusps.
Features of the root:
- The mesial and distal roots are visible.
Mesial aspect:
The mesiolingual and the distolingual cusps are seen.
Features of the crown:
Shape and surface:
- Shape: Rhomboidal.
- The surface is convex and smooth.
- The crown is lingually inclined on the root.
- The mesial contact area in the centre of the crown is buccolingually.
Buccal outline:
- The buccal outline is convex from the cervical line in the area of the Buccal cervical ridge and less convex till the cusp tip.
Lingual outline:
- It is straight or less convex than the buccal outline.
Occlusal outline:
- The mesiolingual and the mesiobuccal cusps are seen with the mesial Marginal ridge.
- The occlusal surface is narrower buccolingually than the first molar.
Cervical line:
- The cervical line is straight and regular.
Features of the root:
- The mesial root is seen. It has a pointed apex.
- Often a part of the distal root might be visible buccally in comparison to the distal root being visible from the lingual aspect in the first molar.
Distal aspect:
Features of the crown:
Shape and surface:
- The shape is rhomboidal.
- The distal cusp is absent in comparison to the first molar.
The distal aspect is similar to the mesial aspect except for the following variations:
- The distal marginal ridge is more cervically placed than the mesial marginal ridge and thus more of the occlusal surface is seen.
- The tooth converges more towards the distal aspect and thus more of the buccal and lingual surface is seen.
Features of the root:
- The distal root has a pointed apex.
Occlusal aspect:
Shape and surface:
- The shape is rectangular.
- There is cervical prominence on the mesiobuccal lobe.
- The mesial outline is squarish.
- The distal outline is semicircular due to the curvature of the crown distally than mesially.
- The mesiodistal dimension is more than the labiolingual dimension.
- The degree of lingual convergence is less than the first molar and thus the tooth is as wide buccally as lingually. The rest of the occlusal surface is described in the table.
Occlusal surface of the mandibular second molar:
The features that can help in the identification of the mandibular second molar are given in the box.
Features to identify the mandibular second molar:
Four cusps
- Two roots
- The crown is narrower on the mesial side than on the distal side
Differentiation Between The Mandibular Left And Right Second Molar
- From the buccal aspect, the crown tilts distally.
- The crown is wider mesially than distally.
- The distal marginal ridge is more cervically located than the mesial marginal ridge.
Development And Landmarks Crown And Root Of The Mandibular Second Molar
The Permanent Mandibular Molars Synopsis
Buccal aspect:
The two buccal cusps and part of the lingual cusps might be seen.
Crown:
- The crown is shorter cervico-occlusally and narrower mesiodistally than the first molar.
- The buccal surface contains the buccal developmental groove separating the mesiobuccal and the distobuccal cusps.
- The mesial contact area is located at the junction of the middle and the occlusal third.
- The distal contact area is located in the middle of the middle third.
Root:
- There are two roots – mesial and distal.
Lingual outline:
Crown:
- The lingual convergence is lesser than in the first molar and thus lesser portion of the mesial and the distal surfaces is seen.
- The mesiolingual and the distolingual cusps are seen separated by the lingual developmental groove.
- The lingual cusps are placed higher than the buccal cusps.
Root:
- The mesial and distal roots are visible.
Mesial aspect:
The mesiolingual and the distolingual cusps are seen.
Crown:
- The shape is rhomboidal and the surface is convex and smooth.
- The mesiolingual and the mesiobuccal cusps are seen with the mesial marginal ridge.
- The occlusal surface is narrower buccolingually than the first molar.
Root:
- The mesial root is seen.
- It has a pointed apex.
- Often a part of the distal root might be visible buccally in comparison to the distal root being visible from the lingua aspect in the first molar.
Distal aspect:
Crown:
- The shape is rhomboidal.
- The distal cusp is absent in comparison to the first molar.
- The distal marginal ridge is more cervically placed than the mesial marginal ridge and thus more of the occlusal surface is seen.
Root:
- The distal root has a pointed apex.
Occlusal aspect:
- The shape is rectangular.
- The mesiodistal dimension is more than the labiolingual dimension.
- The degree of lingual convergence is less than the first molar and thus the tooth is as wide buccally as lingually.
- The four cusps are mesiolingual, mesiobuccal, distobuccal and distolingual.
The Permanent Mandibular Third Molar
The mandibular third molars are the posteriormost teeth in the lower jaw and are distal to the second molar. They exhibit huge variation in form, size, shape and position. They supplement the second molar in function. The crown is not well developed and the occlusal form of the tooth resembles the second molar.
- Generally, the third molar has four cusps, but sometimes it might have five cusps and thus much larger in size and may not occur with the antagonist.
- The huge crown may not even fit into the lower jaw due to the lack of space.
- The roots are smaller in size and might be fused and generally malformed.
- The mandibular third molars are most often wholly or partially impacted due to lack of space in the jaw.
- The morphology of this tooth will be described from the buccal, lingual, mesial, distal and occlusal aspects.
- The nomenclature, chronology and measurement of the mandibular third molar are given in tables.
Nomenclature: Mandibular third molar:
Mandibular third molar: Chronology and measurements:
Buccal aspect:
Features of the crown:
- The shape is trapezoidal.
- The service-occlusal length of the crown is either the same or smaller than the mandibular second molar.
- The crown is wider mesiodistally than at the cervix.
- The buccal cusps are rounded and short and are separated by the buccal Developmental groove.
- The mesial and distal contact areas are occlusal to the centre of the crown cervicoocclusally.
- The cervical line is irregular or straight.
Features of the root:
- Generally, there are two roots, mesial and distal.
- The roots are poorly developed and short compared to the other mandibular molars and more distally inclined.
- Often the roots are fused along the entire length or partially.
Lingual aspect:
- It is similar to the buccal aspect.
- The mesiolingual and distolingual cusps are visible.
- They are separated by the lingual developmental groove.
Mesial aspect:
- It is similar to the mandibular second molar but smaller in size.
- The crown is rhomboidal in shape.
- The mesiobuccal and mesiolingual cusps are visible.
- The buccal crest of curvature is at the cervical third.
- The lingual crest of curvature is at the middle third.
Distal aspect:
- It is similar to the mandibular second molar but smaller in dimension.
- If the tooth is larger in size then it’s more rounded above the cervical line.
- The tips of the distobuccal and distolingual cusps are lower than the Mesiobuccal and mesiolingual cusps.
- Most of the occlusal surface is seen as the distal marginal ridge placed at a lower and curved cervically.
Occlusal aspect:
Features of the crown:
- The mesiodistal diameter of the crown is more than the buccolingual diameter.
- The crown is wider mesially than distally.
- The crown is similar to the second molar.
- Four-cusp or five-cusp forms might be seen.
- The groove pattern might have the ‘ +’ or the y pattern.
- A well-developed mandibular third molar resembles the second molar.
Features of the root:
- The roots are undeveloped and shorter than the mandibular second molar.
- If there are two roots, i.e. The mesial and distal they might be separate but most often are fused. The fusion might be partial or along the entire length of the root.
- The roots might have a distal tilt.
Development And Landmarks Crown And Root Of The Mandibular Third Molar
The Permanent Mandibular Molars Synopsis
Buccal aspect:
Crown:
- Shape is trapezoidal.
- The crown is wider mesiodistally than at the cervix.
- The mesial and distal contact areas are occlusal to the centre of the crown cervicoocclusally.
Root:
- The roots are poorly developed and short compared to the other mandibular molars and more distally inclined.
- Often the roots are fused along the entire length or partially.
Lingual aspect:
Crown:
- It is similar to the buccal aspect.
- The mesiolingual and distolingual cusps are visible. They are separated by the lingual developmental groove.
Mesial aspect:
Crown:
- The crown in rhomboidal in shape.
- The buccal crest of curvature is at the cervical third.
- The lingual crest of curvature is at the middle third.
Distal aspect:
Crown:
- The tips of the distobuccal and distolingual cusps are lower than the mesiobuccal and mesiolingual cusps.
- Most of the occlusal surface is seen as the distal marginal ridge is placed at a lower and curved cervically.
Occlusal aspect:
Crown:
- The mesiodistal diameter of the crown is more than the buccolingual diameter.
- The crown is wider mesially than distally.
- The groove pattern might have the ‘+’ or the y pattern.
- A well-developed mandibular third molar resembles the second molar.
Root:
- The roots are undeveloped and shorter than the mandibular second molar.
- The roots might have a distal tilt.
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