Posterior Dental Anatomy

University of Honolulu

Heights of contour

Premolars: Facially on cervical 3rd, Lingually on middle 3rd

Molars: Facially on gingival 3rd, Lingually on middle 3rd

Name all posterior contacts from facial

Mesial: Middle 3rd, close to junction of occlusal and middle (more occlusal)

• except mandibular 1st premolar, has distal contact more occlusal

Distal: Middle 3rd

Are premolars succedaneous or nonsuccedaneous? why?

Yes, they replace the primary molar’s position (primary dentition has no premolar)

Premolar facial cusp tip vs Cusp ridge

• All cusp tips mesial to mid-root axis except maxillary 1st premolar which is distal

• All cusp ridges are distally longer, except maxillary 1st molar which has mesial side longer

Ridges correspond to the opposite of tips, if tip is mesial, then the distal is inevitably going to be longer

Posterior Teeth Marginal Mesial vs Distal Ridge more occlusal (occlusal height)

All mesial ridges are more occlusal except the mandibular 1st premolar which has a more occlusal distal marginal ridge

MD vs. FL width

All teeth in dentition are FL wider than ML, except:

• Mandibular molars

• Maxillary central and lateral incisors

How many cusps in pre-molars? Any exceptions?

Most have 2 cusps except mandibular 2nd premolar can have 3

Crown shapes of maxillary pre-molars

Facially a pentagon like the canines

• 1st are longer, sharper cusps than second and more prominent buccal ridge

Maxillary Proximally a trapezoid

Premolar Occlusal shape

Maxillary 1st: oblong, asymmetrical, bent mesially on lingual

Maxillary 2nd: oblong, more symmetrical, oval

Mandibular 1st: square/diamond

Mandibular 2nd: round oblong oval (2cusp) or square (3cusp)

• Note: most lingual cusps converge towards mesial

M and D contact areas from occlusal view (Maxillary Premolars)

Maxillary 1st: distal more B than mesial

Maxillary 2nd: mesial more B than distal

Crown tilt of posterior teeth (L inclination)

Maxillary: crown aligned with root

Mandibular premolars: Both tilted but 1st is noticeably more tilted towards lingual

• need to tilt drill to not perforate side

Mandibular molars: tilted towards lingual

Developmental Lobes in Premolars, exceptions?

Similar to anterior teeth

• 3 buccal and 1 lingual/palatal lobe = 4 lobes

  • except mandibular 2nd: usually (54%) has 2 lingual = 5 lobes

• 2 buccal depressions

Premolar Ridges

2 triangular ridges join to form a transverse ridge in all premolars except the mandibular 2nd premolar, which can have 3 ridges and no transverse ridges

Maxillary 1st premolar Root form

• 2 roots (67%)

• root bifurcation (separation) happens at apical third

• palatal root shorter than buccal

• usually cannot see palatal root from facial

• root relatively straight and taper towards palatal

• mesial depression is deeper and goes from bifurcation to MMR Groove

• CEJ more curved on Mesial

Maxillary 2nd premolar Root form

• 1 root

• distal depression deeper

• depression does not reach crown

• root longer than maxillary 1st premolar

• CEJ more curved on mesial

Maxillary 1st Premolar KEY FEATURES

• usually 2 roots

• Only tooth with mesial marginal ridge (MMR) Groove

• only tooth that has root depression deeper on mesial

• mesial crown concavity

• mesial root depression resulting from bifurcation can be the cause of periodontal disease

• Only premolar with cusp tip towards distal and mesial cusp ridge longer

Maxillary 2nd Premolar KEY FEATURES

• longer root than 1st maxillary premolar

• looks like a skinnier/symmetrical version of the 1st but no MMR groove

Eruption order

• max 1st premolar: 10-11yoa

• max 2nd premolar and man 1st: 10-12yoa

• mand 2nd premolar: 11-12

max 1st > max2nd = mand1st > mand2nd

Maxillary pre-molars: Occlusal anatomy

Both have mesiobuccal/palatal and distobuccal/palatal grooves, a central groove and two triangular fossa&pit

• maxillary first has a longer central groove and thus a greater space between the fossas&pits

• maxillary central has grooves on mesial meet the marginal ridge

Lingual vs Buccal Cusp Height in Premolars

Lingual always shorter

Crown shapes of Mandibular Premolars

Facially a pentagon like the canines

• 1st are longer, sharper cusps than second. Overall both less prominent than maxillary buccal ridges

• 2nd has wider crown (proximal view)

• may have developmental notches (Bumps from cusp to cusp)

• 2nd may have two cusps on lingual, and thus a lingual ridge to separate the two cusps

• 2nd has less lingual convergence than 1st

Proximally a rhomboid

Mandibular 1st Pre-molar Root Form

• straight or curves distal (58%)

• single root maybe be divided in apical third

• depression on distal side deeper than mesial

Mandibular 2nd Pre-molar Root Form

• root wider than 1st

• no mesial depression, distal depression

Maxillary Premolar Lingual Cusps bend towards?

mesial

Mandibular 1st Pre-molar KEY FEATURES

• mesiolingual groove (69%)

• distal marginal ridge more occlusal (mesial more cervical)

• most pronounced transversal ridge

• Tilts more towards lingual

• root may divide in apical third

• lingual cusp smaller not functional

Mandibular 2nd pre-molar KEY FEATURES

-2 or 3 cusps

-lingual groove in 3 cusp

• Only tooth with No depression on distal

Mandibular pre-molars: Occlusal anatomy

1st pre-molar: “little y” shape

• diamond outline

• mesiolingual groove

2nd premolar (2 cusp type): “U” shape

• curved central groove

• triangular ridge on lingual is smaller

• distal triangular fossa larger (has more supplemental grooves)

• round outline

2nd premolar (3-cusp-type): “big Y” shape

• 3rd cusp is distolingual

• has a central fossa

• buccal cusp larger, lingual cusps much smaller than on first

• 3 triangular ridges no transverse ridge (none are across from each other)

• lingual groove off the bottom of the Y

• more squared outline, wider on lingual

• 3rd cusp may be non-functional

What is the largest tooth type in each arch

• what is the largest tooth overall in permanent dentition?

Molars

• Maxillary 1st molar

Are molars succedaneous?

No, they occupy a space that is empty in primary dentition

What tooth type has the broadest Occlusal surface

The molars do, which makes sense as they do most mastication and grinding

Which tooth type has the shortest crowns CO (Cervical-Occlusal)

Molars have the shortest CO

M vs D crown height on all molars

distal height is always lower

Crown shapes of Maxillary molars

Maxillary 1st:

• occlusal: parallelogram/rhomboid with more acute angles being MB and DL (pointing towards mesial)

• facial: trapezoid with buccal ridge separating MB and DB cusps up to middle 3rd.

  • MB cusp longer and lingual cusps show slightly

• lingual: trapezoid, lingual ridge reaches middle 3rd,

  • ML taller than DL

• proximal: 2 cusps visible mesial (+carabelli if present), 4 cusps visible on distal (+ carabelli if present)

  • MMR longer and more occclusal than D, therefore you can see MMR from distal but not DMR from mesial

Maxillary 2nd:

• occlusal:

  • 4 cusp: twisted parallelogram, less squared, same but more acute angles than 1st, tapers from B-L more than 1st

  • 3 cusp: heart shaped, tapers BL

• facial: trapezoid

  • buccal groove is shorter than 1st (doesn’t reach middle 3rd)

  • MB is considerably taller than DB (almost the same on 1st)

• lingual: trapezoid

  • 2 visible cusps on 4 cusp type, lingual groove does not reach middle 3rd

  • 1 visible cusp on 3-cusp type, so no lingual groove

• proximal: trapezoid shape, same as 1st but

  • no carabelli cusp, DL cusp may be missing if it is a 3 cusp type

  • M view has little occlusal visible, distal view has more visible

Crown shapes of Mandibular molars

Mandibular 1st:

• occlusal: pentagonal (MD widest), tapers towards lingual

• facial: trapezoidal crown

  • MB cusp longer than DB

  • DB sharper

  • ML tallest cusp and DL can be seen from this view

  • M outline straight, D convex

• lingual:

  • Lingual cusp tips sharper than buccal tips

  • L cusps are nearly equal in size and hide B cusps

• proximal: rhomboid

  • tilted towards lingual

  • cannot see much occlusal surface from mesial, can see more from distal

Mandibular 2nd:

• occlusal: oblong rectangle, tapers less to B-L than 1st

  • M outline straight, D convex

• facial: more pronounced buccal cervical ridge

  • tapers less toward cervical than 1st because of absence of D cusp

  • MB taller and wider than DB

  • ML and DL cusps can be seen

  • 1B groove that may end in a pit

• lingual:

  • can’t see B cusps

  • CEJ straight

• proximal:

  • less wide FL than 1st

  • lingual tilt

  • cant see much occlusal surface from mesial

  • can see some occlusal surface from distal

Root shapes of Maxillary Molars

Maxillary 1st:

FACIAL AND LINGUAL VIEWS

• CEJ less curved on distal

• 3 roots: palatal, MB, DB ( tallest to shortest, same order as cusp height)

  • roots are twice as long as crown

  • MB and DB roots have plier form and shape is as wide as crown

  • palatal root has longitudinal depression

• 4 canals (2MB, 1DB, 1 palatal)

PROXIMAL VIEW

• MB root wider than DB and extends beyond crown

  • has longitudinal depression

• Palatal root looks like banana also extends beyond crown

• root trunk (trifurcation) at cervical and middle junction

• DB root thinner than MB and does not extend past crown

  • no depression, has concavity close to CEJ on distal

Maxillary 2nd: similar to 1st with some differences

FACIAL AND LINGUAL VIEWS

• 3 roots and 4 canals, but lower incidence of 2nd MB canal

• MB and DB roots more parallel and less separated

• Roots rarely extend beyond crown

• root trunk longer than 1st maxillary molar

• more distal bend

PROXIMAL VIEW

• root trunk longer than 1st maxillary molar

Root shapes of Mandibular Molars

1st:

FACIAL AND LINGUAL VIEWS

• 2 roots (D shorter, 3 canals (2M,1D)

• roots twice as long as crown, highest root/crown ratio

• roots narrower on lingual

• root bifurcation closer to CEJ than in maxillary

  • root trunk is longer on lingual

• longitudinal depression between root bifurcation reaches crown

• Both roots are usually distally inclined

  • M root curves towards mesial for first half and then deflects distally for second half

  • D root straighter

• CEJ straight or irregular and more occlusal on lingual

PROXIMAL VIEW

• M longer and wider than D root

• deep depression on M root

2nd:

FACIAL AND LINGUAL VIEWS

• 2 roots, 3 canals ( M taller and wider)

• root trunk very close to CEJ but longer than in 1st

• M and D roots more parallel and close together than 1st

• roots sharper than on 1st

• CEJ nearly straight

• longitudinal depression from furcation to crown

PROXIMAL VIEW

• less broad M root than 1st

• M root depression

• M root visible from distal

Maxillary Molars Occlusal Anatomy

1st:

• 4 cusps: ML, MB, DB, DL (largest/tallest to smallest/shortest)

• Primary cusp triangle are the biggest 3 cusps (ML,MB,DB)

• May have nonfunctioning Cusp/depression of Carabelli between ML and DL

• Transverse ridge (ML and MB) and Oblique ridge (DB and MB), Lone Triangular ridge (DL)

• 4 fossa: Central, DL, M, D (deepest to shallowest)

• 5 developmental grooves (make a Gemini looking sideways I) : Transverse groove central groove, buccal groove, distal oblique groove, lingual (D) groove

  • Stuart Groove ay be present as continuation of buccal ridge into MB cusp

  • 5th cusp Carabelli groove: may be present

2nd: 4-cusps type (2/3) follows the same morphology as 1st with some differences:

• More variation in DL cusp size

• smaller oblique ridge

• no 5th cusp of carbelli

• many more supplemental grooves and pits, especially in oblique ridge

2nd: 3-cusp type (1/3): similar morphology as 1st but missing features

• DL cusp missing = 3 cusps total

• 3 grooves ( horizontal Y with arms towards mesial): central groove, buccal groove and transverse groove

  • no oblique ridge

Mandibular Molars Occlusal Anatomy

1st:

• 5 well-developed cusps: ML, DL, MB, DB, D (longest to shortest)

  • MB is still the largest/bulkiest overall

• 2 Transverse ridges: MB&ML and DB&DL

  • D cusp is a lone triangular ridge

• 3 fossae: Central fossa, mesial fossa, distal fossa (largest to smallest)

• 4 developmental grooves (slingshot shape): central groove, Lingual groove, MB groove, DB groove

2nd: very similar to 1st but D cusp missing

• 4 cusps: ML, DL, MB, ML (longest to shortest)

• no D triangular ridge

• 2 transverse ridges: MB&DB and DB&DL

• 3 fossa: central, M, D

• 3 developmental grooves (cross shape): Central, Buccal and Lingual

Occlusal view of contacts for molars

Mesial contact on 1st are more buccal than distal contact

• mesial contact for 2nd molar match the 1st molar’s distal, but the distal contact for the 2nd molar cannot be predicted due to the morphology of the 3rd molar being so varied

3 longest max roots in order

1. maxillary canine

2. maxillary 2nd premolar

3. maxillary 1st molar

Maxillary 3rd Molars vs Mandibular 1st molars

Both

• greatest morphologic variance

• bulbous crowns, short roots

Max

• 20% of population never develop 1 or more

• shortest of all permanent teeth

• long root trunks

• may resemble 1st or 2nd maxillary molars

• smaller than 1st and 2nd maxillary molars

• lots of supplemental grooves

• small occlusal surface

• 1-8 cusps

Mand

• shortest of all mandibular teeth

• root fused

• may resemble 1st or 2nd mandibular molars

Mandibular 1st molar KEY FEATURES

• largest MD dimension of any tooth

• largest root/crown ratio of any tooth

Curve of Wilson

even though ML and DL cusps are taller on mandibular molars, the teeth are positioned on the arch in a way that they tilt towards lingual, therefore the MB cusp looks taller when the tooth is in the mouth

Mesial FL ridge vs Distal FL ridge length

mesial is always longer than distal, therefore it makes less sharp V

• except mandibular 2nd premolar that has shorter mesial FL ridge

Maxillary 1st Molar KEY FEATURES

root concavity on distal