Morphology Of Mandibular Molars

Morphology Of Mandibular Molars

Mandibular Molars Mandibular first molars have five cusps, arranged in height from longest to shortest; mesiolingual, distolingual, mesiobuccal, distobuccal and a smaller distal cusp.

Mandibular second molars have four cusps, in order from the longest to shortest -mesiolingual, distolingual, mesiobuccal and distobuccal. The crown of the mandibular second molar is usually smaller than that of the first molar.

First Molar The mandibular first molar has the largest mesiodistal dimension of any tooth - 11.4 mm on the average. The mesiolingual cusp is highest and widest. The mandibular first molar usually has 3 buccal cusps (81%) - mesiobuccal, distobuccal and distal. The mesiobuccal cusp is the largest, widest and highest cusp on the buccal side. The distobuccal cusp is slightly smaller, shorter, and sharper than the mesiobuccal cusp.

The distal cusp is the smallest of the 5 cusps, and is missing in about 20%.

The mesiobuccal groove separates the mesiobuccal cusp from the distobuccal cusp.

Sometimes there is a deep pit at the cervical end of this groove. The distobuccal groove separates the distobuccal from the distal cusp. In the mouth, the lingual cusp tips are at a lower level than the buccal cusps due to the lingual tilt of the root axis in the mandible.

Second Molar The mandibular second molar has 4 cusps mesiobuccal, distobuccal, mesiolingual and distolingual. As on the first molar, the mesiobuccal cusp is usually wider mesiodistally than the distobuccal cusp. The lingual cusp tips are visible from the buccal side. There is only one groove - buccal groove, that separates the mesiobuccal and distobuccal cusps, and extends to the middle of the buccal surface in a pit.

Distal contacts are more cervical than mesial contacts. The cervical line of both mandibular molars runs nearly straight across the buccal surface. Both mandibular first and second molars have two roots, a mesial root and a distal root, approximately the same length. The roots are nearly twice as long as the crown.

The root bifurcation of the mandibular first molar is near the cervical line, with a depression between them. The root trunk is shorter than on the second molar, as the roots of the first molar are widely separated, on the second molar they are more parallel.

The apical half of the roots curve distally. The distal root is straighter than the mesial root and may have a more pointed apex. The roots of the second molar are more pointed than the roots of the first molar. Both roots may curve distally, and the mesial one is slightly longer than the distal. Mandibular first and second molar crowns are narrower on the lingual side, more so on first molars.

The lingual cusps of mandibular molars are both slightly longer and more pointed or conical than the buccal cusps, which are hidden behind them. The lingual groove

separates the mesiolingual from the distolingual cusp, terminating on the lingual surface. The cervical line is relatively flat or irregular. From proximal - wide and short crowns. Mandibular molar crowns are relatively shorter cervico-occlusally compared to buccolingually. The crowns of both mandibular molars are tilted lingually from the root base -distinguishing mark for all mandibular posterior teeth.

The crest of curvature of the buccal surface is in the cervical third. It is called the buccal cervical ridge (margo buccalis cervicalis), running in a mesiodistal direction on the buccal surface of the crown.

The mesial marginal ridge is concave buccolingually, usually V-shaped on the second molar. The distal marginal ridge is more cervically located than the mesial one and it may have a groove crossing it.

The Roots From the mesial aspect, the mesial root of the first molar is broad buccolingually, hiding the distal root. It has a blunt apex. On the second molar, the mesial root is less broad buccolingually, narrow in the cervical third, and with a more pointed apex. The mesial root always has two root canals - one buccal and one lingual. The distal root is shorter and more pointed at the apex.

From the occlusal aspect the shape of the second molar is rectangular, whereas the first molar is like a pentagon due to the small distal cusp. The two mesial cusps are larger than the two distal cusps. Considerable portion of the buccal surface is visible due to the lingual inclination of the crown. Both molars are wider mesiodistally than faciolingually. The crown tapers two ways - distally and lingually. This mark is helpful in distinguishing lefts from rights and mesial from distal.

The widest buccolingual dimension of the crown is at the buccal cervical ridge. On both first and second molars, the triangular ridges of the mesiobuccal and mesiolingual cusps meet to form a transverse ridge. Another transverse ridge is formed by the triangular ridges of the distobuccal and distolingual cusps.

There are three fossae on mandibular molars - large central fossa, mesial triangular fossa, and a small distal triangular fossa.

The Grooves The groove pattern on second molars resembles a cross. The central groove extends through the central fossa from the mesial triangular fossa to the distal triangular

fossa. The buccal groove separates the mesiobuccal and distobuccal cusps and is usually continuous with the lingual groove that separates the two lingual cusps.

Marginal ridge grooves occur more frequently on the mesial. Supplemental grooves are named according to their location. Supplemental ridges are positioned between major and supplemental grooves and serve as additional cutting blades.

The grooves on the mandibular first molar separate five cusps and the pattern is more complicated. There are several grooves - the central groove is zigzag-shaped and extends through the central fossa from the mesial triangular fossa to the distal triangular fossa.

The lingual groove extends lingually between the mesiolingual and distolingual cusps onto the lingual surface. The mandibular first molar has two buccal grooves mesiobuccal groove and distobuccal groove, separating the three buccal cusps. There are numerous supplemental ridges and grooves named according to their location.

The marginal ridges are crossed by a groove, more often on the mesial. In 20% the mandibular first molar has four instead of five cusps.

The crown of the mandibular third molar resembles the crown of the first or second mandibular molar, but is extremely variable. It is generally characterised by a very convex crown and short roots. The lingual cusps are larger and longer than the buccal cusps.

The mesiobuccal cusp is the largest of the buccal cusps. Irregular groove pattern with numerous supplemental grooves and pits on the occlusal surface that produce a wrinkled appearance. Occlusal outline - rectangular of oval mesiodistally, with small occlusal table. Two roots, mesial and distal, often fused together, more curved distally compared to first and second molars and sometimes with extreme curvature.

Frequently one or more extra roots are apparent.