mandibular molars

Mandibular Molars

Howard Chi, D.M.D.

Learning Objective

• Anatomy of the mandibular molars

Buccal Aspect Of Mandibular Molars

• Crown Shape– The crowns of

mandibular molars are wider mesiodistally than high cervico-occlusally (greatest extent on first molars)


• First Molar Cusps– The mesiolingual cusp is the highest and widest

– The first molar has the largest mesiodistal dimension

of any tooth

– First molars usually possess three buccal cusps

123


• First Molar Cusps– The mesiobuccal is the largest, widest, and highest

cusp on the buccal side

– The distobuccal cusp is slightly smaller, shorter, and may be sharper than the mesiobuccal

– Distal cusp is on the DB line angle and is the smallest of the five cusps

LMS

DB Line angle


• First Molar Cusps– The distolingual cusp is the second highest cusp when

the tooth is oriented vertically

– Even though the lingual cusps are higher than the buccal cusps, clinically the lingual cusp tips are at a lower level than the buccal due to the lingual tilt of the tooth

2nd highest


• Grooves Of The First Molars– The mesiobuccal groove separates the mesiobuccal

and distobuccal cusp

– There may be a deep pit at the cervical end of this groove

– This pit can be a site of caries

MB groove

Buccal Pit


• Grooves Of The First Molar– The distobuccal groove separates the distobuccal

cusp from the distal cusp

– It is shorter than the MB groove and not frequently pitted

DB groove


• Second Molar Cusps– Four cusps are present on lower second molars

– MB cusp is usually wider mesiodistally than the DB cusp

– The lingual cusp tips are usually visible from the buccal aspect

D M


• Grooves Of The Second Molar– The buccal groove separates the MB cusps from the

DB cusp

– May end in the middle of the buccal surface in a pit

D M

Buccal groove


• Proximal Contacts– Same as all molars

– Mesial: Junction of the occlusal and middle thirds

– Distal: Middle third of crown


• Cervical Line– CEJ is nearly straight across the buccal surface on lower

first and second molars

– Occasionally a point of enamel will dip down nearly into the root bifurcation

– Can also have this type of projection on the lingual, this could lead to periodontal problems

Enamel projection


• Taper To The Cervical And The Distal– There is proportionally more tapering of the crown

from contact areas to the cervical line on first molars than second molars because of the bulge of the distal cusp

#31 #30


• Variations In Mandibular Molar Crowns– The distal cusp is absent one fifth of the time

– A four-cusp molar may not always be a second molar - rely on tooth position to aid in determination

Absent 1/5 of the time

Roots Of Mandibular Molars

• Both mandibular first and second molars

have two roots (one mesial and one distal)• Both roots are nearly twice as long as the

crown


• The root bifurcation of a mandibular first molar is near the cervical line

• A depression exists between the cervical line and bifurcation

• The root trunk relatively short (shorter than lower second molars)

Root depression Short root trunk


• Roots of first molars are widely separated• Second molars have more parallel roots• Roots may possess a distal curve in the

apical portion

Note distal bend in root


• From the buccal aspect can

see the distal surface of the mesial root because it is twisted on the trunk

• The distal root is straighter than the mesial root and may possess a pointed apex

• The apex of the mesial root may be in line with the mesiobuccal groove

Lingual Aspect Of Mandibular Molars

• Crown Shape From The Lingual– Mandibular first and second molar crowns taper to

the lingual

– This lingual taper is more evident in first molars

– The lingual cusps are longer and more pointed than the buccal cusps

#30


• Crown Shape From The Lingual– The mesiolingual cusp is usually longer and

wider (slightly) than the distolingual cusp

#30

ML DL


• Grooves– The lingual groove separates the mesiolingual cusp

from the distolingual cusp

– Terminates in the occlusal third with no pit


• Cervical Line– The CEJ is relatively flat mesiodistally

– Can dip cervically between the roots over the bifurcation (similar to buccal)

– A depression can be seen between the cervical line and the bifurcation

Roots Of Mandibular MolarsFrom The Lingual

– On first molars, root trunk appears longer on the lingual than the buccal

– This is due to the fact that the cervical line is more occlusal on the lingual surface

Roots Of Mandibular MolarsFrom The Lingual

• The roots are narrower on the lingual aspect than the buccal

• Can often see the mesial aspect of the mesial root due to the twisting on the trunk

• Can see the distal side of the distal root because of taper to the lingual

Mesial

Proximal Aspect Of Mandibular Molars

• Crown Shape From The Proximal– Appear relatively short occlusocervically compared

to faciolingual dimension

– The crowns are tilted lingually on the root base

– The buccal outline is convex in the cervical third


• Crest Of Curvature– The height of contour on the buccal surface is

within the cervical third

– On molars this buccal bulge is called the buccal cervical ridge

– It is more prominent on second molar than first molars

#30


• Cusp Height– The lingual cusps are more conical and pointed

than the buccal

– They are the largest of the four to five cusps

#30

Proximal Aspect Of Mandibular

Molars

• Distal Tilt– Due to the distal tilt of the crown and the sloping of

the occlusal surface, most of the occlusal surface and all cusps can be seen from the distal

#30 Distal #31 Distal


Molars

• Taper To The Distal– On both first and second molars the crown is more narrow

on the distal than the mesial

– Can see some of the buccal and lingual surface from the distal due to this taper

#30 Distal #31 Distal


Molars

• Cervical Line– The mesial CEJ of both first and second molars slopes

occlusally from buccal to lingual

– The distal cervical line is nearly straight


• Marginal Ridges– The mesial marginal ridge is concave buccolingually

– Usually longer on first molars than second and

V-shaped on the second

Occlusal Aspect Of Mandibular Molars

• Lingual Inclination– Due to lingual inclination a considerable portion of

the buccal aspect can be seen from this view

– The molars are wider mesiodistally than faciolingually


• Shape: Rectangular Or Pentagon– The second molar is roughly rectangular

– The first molar with the distal cusp is more like a pentagon

– The two mesial cusps are larger than the two distal cusps

D M M D


• Taper To The Distal And Lingual– The crown is narrower buccolingually on the distal

than the mesial

– The crown is narrower mesiodistally on the lingual than the facial

D M M D


• Taper To The Distal And Lingual– The widest portion of the crown of a second molar

buccolingually is opposite the mesial cusps

– The widest portion of the crown of a first molar buccolingually is opposite the distobuccal cusp

D M M D


• Ridges– On both first and second molars the MB and

ML cusp’s triangular ridges

form a transverse ridge– The same is true for the DB

and DL cusps– Since lingual cusps are taller, they possess

longer triangular ridges than the buccal


• Fossae– Mandibular molars possess three fossae, a large

central fossa, a smaller mesial, and the smallest distal fossa

– Each or all may possess a pit


• Grooves: First Molar– The central groove is more zigzag or crooked in its

mesiodistal course

– There are two buccal grooves instead of one found on lower second molars

MB GrooveDB Groove


• Grooves: Second Molar– Groove is simpler than first and resembles a cross

– Central groove is straighter than that of the first molar

– Buccal and lingual grooves are usually continuous

Mandibular Third Molars

• Shape And Relative Size– Shortest of mandibular teeth

– Crown may resemble a first or second molar

– Generally have bulbous crowns

#32 Buccal#32 Distal


• Distal Tip– The crown tips distally and the distal half of the

crown is noticeably shorter


• Cusp Size– Lingual cusps are the longest and largest, with ML

being biggest

• Grooves– Irregular groove pattern with multiple

supplemental grooves


• Roots– The two roots tend to be short and are often fused

– If the roots are separate the root trunk will be long

– Can possess one or more extra roots

#32 Lingual #32 Mesial

mandibular molars

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