Molar Anatomy

General Description of Molars

• There are 12 permanent molars: 3 on each side, both on the upper and lower arch
• Under universal numbering system, they are numbered 1,2,3,14,15,16,17,18,19,30,31,32
• The first molars are centered in the arch anteroposteriorly, making their loss devastating to arch continuity
• Molars are the largest and strongest teeth in the arch
• Can be congenitally missing, with 1 or more of the third molars missing in nearly 20% of the population

Function of Molars

• Play a major role in the mastication of food (chewing and grinding)
• Loss of first molar can result in more than 80mm of chewing surface gone
• Important in maintaining vertical dimension of the face
• Important in maintaining continuity within dental arches, thus keeping other teeth in alignment
• Function in esthetics by keeping the cheeks full and keeping chin proper distance from the nose

Class Traits of Molars

• Crown size and shape:
  • Have occlusal surfaces with three to five cusps
  • Have broader occlusal surfaces than other teeth
  • Crowns of molars are wider mesiodistally
  • Are shorter occlusocervically than other teeth
• Taper from buccal to lingual: Molar crowns taper to the lingual
• MTaper to the distal: From an occlusal view, all molar crowns taper distally
• Contact areas:
  • Mesial: At or near the junction of the occlusal and middle thirds
  • Distal: Middle third

Arch Traits of Molars

• Maxillary:
  • Crown shape: Square/parallelogram (B-L > M-D)
  • Number and relative size of cusps: 4-5 cusps (DB, DL, MB, ML, Cusp of Carabelli)
  • Crown centered over roots
  • ML cusp: Largest and longest; connects to DB cusp by the Oblique Ridge
  • ML > MB > DB > DL
• Mandibular:
  • Crown shape: Rectangular/pentagonal (M-D > B-L)
  • Number and relative size of cusps: 4-5 cusps (MB, ML, DB, DL, Distal cusp)
  • ML and DL cusps are nearly equal in size
  • Distal cusp is minor fifth cusp, found on the first and sometimes third molars
• B mandibular tilt: All mandibular teeth, including molars, tilt lingually when viewed from mesial or distal
• Roots of maxillary molars:
  • MB, DB, and Palatal roots
  • Roots are nearly twice as long as the crown
  • Relative length: Palatal > MB > DB
• Roots of mandibular molars:
  • Two roots (Mesial and Distal)
  • Mesial root is usually slightly longer than distal root
  • Mandibular root trunks are shorter than maxillary root trunks, especially on first molars

Anatomy of Maxillary Molars

• Type traits of maxillary 1st and 2nd molars:
  • Relative size: Second molar is smaller than the first molar in the same mouth, especially M-D
  • 1st Molar is broader than the 2nd Molar
  • 2nd Molar crown is often tipped distally on the root trunk
  • Buccal groove: Lies between buccal cusps and extends on the buccal surface to the middle third of the crown
  • Proximal contacts: Same as for all molars
  • Outline shape: The crown appears to tilt distally at the cervix
  • Roots: Are attached to a root trunk (longer in second molars) at the cervical line
  • Apical to the root trunk there is a split into three roots
• Roots of maxillary 1st and 2nd molars:
  • Trifurcation: Three roots splitting of the root trunk
  • Much variation in the shapes of roots
  • The MB and DB roots are often bent in such a way as to resemble the handles of a pair of pliers
  • The MB and DB roots often curve distally
  • The apical third of the MB root may curve distally enough to put its apex distal to the buccal groove
• Lingual aspect of maxillary molars:
  • Crown: Relative size and taper
  • Number and description of lingual cusps: 1st Molar: Two well-defined cusps, ML and DL; 2nd Molar: Two or three cusps, ML and DL (or no DL)
  • Roots of first molars from the lingual: Depression on the lingual aspect of the palatal root
  • Roots of second molars from the lingual: Note distal bend
• Proximal aspect of maxillary molars:
  • 1st Molar: Cusps 1, 2, 3; Mesial marginal ridge is more occlusal than distal
  • 2nd Molar: Looks much like the first molar, but no cusp of Carabelli is present
• Crest of curvature:
  • On the buccal: Located in the cervical third
  • On the lingual (palatal): In the middle third
• Distal taper:
  • Narrower to distal
  • On both first and second molars, the crown is narrower buccolingually on the distal than the mesial### Molar Teeth
• Molars are narrower on the lingual surface than the buccal surface, except for maxillary first molars with large lingual cusps.

Class Traits of Molars

• From an occlusal view, all molar crowns taper distally.
• Contact areas: mesial (at or near the junction of the occlusal and middle thirds) and distal (middle third).

Arch Traits of Molars

• Maxillary:
  • Crown shape: square/parallelogram (B-L > M-D).
  • Number and relative size of cups: 4-5 cups (DB, DL, MB, ML, and sometimes a fifth cusp, Cusp of Carabelli).
  • ML cusp is the largest and longest, connecting to the DB cusp by the Oblique Ridge.
• Mandibular:
  • Crown shape: rectangular/pentagonal (M-D > B-L).
  • Number and relative size of cups: 4-5 cups (DB, DL, MB, ML, and sometimes a fifth cusp, Distal Cusp).
  • ML and DL cusps are nearly equal in size.
• B Mandibular Tilt:
  • All mandibular teeth, including molars, tilt lingually when viewed from mesial or distal.
  • Crowns tilt distally relative to the long axis of the root.

Arch Traits of Molars (Roots)

• Maxillary:
  • Number of roots: 3 (MB, DB, and Palatal).
  • Root length: nearly twice as long as the crown.
  • Relative length: Palatal > MB > DB.
  • Root Trunk: a broad cervical root base.
• Mandibular:
  • Number of roots: 2 (Mesial and Distal).
  • Mesial root is usually slightly longer than distal root.
  • Mandibular root trunks are shorter than maxillary root trunks, especially on first molars.

Anatomy of Maxillary Molars

• Type Traits of Maxillary 1st and 2nd Molars:
  • Relative size: second molar is smaller than the first molar in the same mouth, especially M-D.
  • 1st Molar is broader than the 2nd Molar.
  • 2nd Molar crown is often tipped distally on the root trunk.
  • Buccal groove: lies between buccal cusps and extends on the buccal surface to the middle third of the crown.
  • Proximal contacts: same as for all molars (mesial: junction of occlusal and middle thirds, distal: middle third).
  • Outline shape: the crown appears to tilt distally at the cervix, making it appear shorter on the distal than the mesial.

Roots of Maxillary Molars

• First Molars:
  • Attached to a root trunk at the cervical line.
  • Apical to the root trunk, there is a split into three roots (trifurcation).
  • MB and DB roots are often bent, resembling the handles of a pair of pliers.
  • The apical third of the MB root may curve distally enough to put its apex distal to the buccal groove.
• Second Molars:
  • Attached to a root trunk at the cervical line.
  • Apical to the root trunk, there is a split into three roots (trifurcation).
  • MB and DB roots are nearly parallel.

Lingual Aspect of Maxillary Molars

• Crown:
  • Relative size and taper: due to the prominent DL cusp, the crown may be as wide or wider on the lingual for the first molar.
  • The crown of the second molar usually appears smaller than the first molar.
• Number and Description of Lingual Cusps:
  • First Molar: two well-defined cusps, ML and DL.
  • Second Molar: two types, 4-cusp or 3-cusp, with or without a DL cusp.

Roots of Maxillary Molars (from the Lingual)

• First Molars:
  • Palatal root is the third longest of any maxillary tooth.
  • Tapers apically to a blunt or rounded apex.
  • There is usually a depression on the lingual aspect of the palatal root.
• Second Molars:
  • The lingual (palatal) root is as long as the lingual root of the first molar.
  • The buccal roots bend towards the distal and are more parallel.

Proximal Aspect of Maxillary Molars

• First Molars:
  • Cusps: 1-2-3.
  • From the mesial, the crown appears broad faciolingually.
  • Two or three cusps can be seen from the mesial (MB, ML, and Cusp of Carabelli).
  • Distal cusps are shorter and generally not seen from the mesial.
• Second Molars:
  • From the mesial and distal aspect, looks much like the first molar, but no cusp of Carabelli is present.
  • DL cusp is absent on more than one-third of these teeth.

Crest of Curvature and Distal Taper

• Crest of Curvature:
  • On the buccal, located in the cervical third.
  • On the lingual (palatal), in the middle third.
• Distal Taper:
  • On both first and second molars, the crown is narrower buccolingually on the distal than the mesial.

Mesial Marginal Ridges and Tubercules

• Mesial Marginal Ridges:
  • On both first and second molars, the mesial marginal ridge is concave and more occlusally located than the distal marginal ridge.
• Tubercules:
  • If present, are usually found on the mesial marginal ridge of first molars (rarely found on 2nd molars or distal marginal ridge of first molars).

Cervical Line and Proximal Contacts

• Cervical Line:
  • The mesial cervical line has a slight occlusal curvature.
  • There is slightly less curvature on the distal than the mesial.
• Proximal Contacts:
  • The mesial contact area is at the junction of the middle and occlusal thirds.
  • The distal contact area is in the middle third.

Roots of Maxillary Molars (from the Proximal)

• First Molars:
  • MB root is broad buccolingually and is shorter than the lingual root.
  • The MB root obscures the view of the DB root.
  • The apex of the MB root is in line with the MB cusp tip.
• Second Molars:
  • On second molars, roots are much less spread apart.
  • The lingual root is also straighter, usually not extending past the confines of the crown.

Occlusal Aspect of Maxillary Molars

• First Molars:
  • The contour of first molars is not square, but gives that impression when compared to other teeth.
  • It is roughly a parallelogram.
• Second Molars:
  • The second molar is wider buccolingually than mesiodistally and tapers to the lingual.
  • Much variation in second molar due to size and location of DL cusp.

Number and Size of Cusps

• Generally:
  • There are four cusps.
  • First molar possesses a fifth cusp 70% of the time.
  • Second molar may be missing the DL cusp.

Oblique Ridge and Fossae

• Oblique Ridge:
  • Unique to maxillary molars.
  • Connects the DB cusp with the ML cusp.
  • Present in second molars, but smaller than the oblique ridge of first molars.
• Fossae:
  • There are generally four fossae on four-cusp molars.
  • On three-cusp molars, the distal fossae and both the distal oblique and lingual grooves are absent.

Maxillary Third Molars

• General Description:
  • Difficult to describe due to great variation.
  • Roots and crown are shorter than the first or second molar.
  • Crown often possesses more supplemental grooves.
  • May possess three, four, or five cusps.
• Mesial Roots:
  • Possess three roots, but more often they are fused for most of their length.
  • Roots are shorter than those of the first and second molar.