Morphology of Molars

MORPHOLOGYOF

PERMANENT MOLARSDental AnatomyDental Anatomy

Dent 201Dent 201Summer semesterSummer semester

2005/200062005/20006

Permanent Molars

Class traits 3 or more cusps At least 2 buccal cusps One or more lingual

cusps In general 2 or 3 roots

Maxillary permanent molars

Arch traits 3 roots: 2 B & 1 L Crown: BL > MD dimension Cusps

• 3 major cusps– ML, MB & DB– Arranged in a tricuspate-triangular

pattern

• Lesser-sized DL cusp & sometimes missing

Oblique ridge: ML to DB cusp B cusps are of unequal size ML cusp is larger than DL

Maxillary permanent molars

Type trait (in general) DL cusp reduces in size

when going posteriorly & may be missing in 3rd molar

1st molar is the largest & shows the least morphological variation

Cusp of Carabelli Roots become more D inclined

& much closer when going posteriorly

Maxillary permanent 1st molar

Buccal aspect MB & DB cusps are of equal

height MB is wider Separated by B groove

• Terminates halfway Slopes of DB are steeper Tip of the ML cusp between B

cusps


Buccal aspect M profile is highly convex in occlusal

2/3s M HOC is ¾ the distance from CL to

MR Cervical 1/3 is flat or concave D profile is entirely convex D HOC is 3/5 the distance from CL to

MR CL is 2 slightly curved segments

separated by apical peak


Buccal aspect Buccal surface

• D surface is visible• Cervical 1/3 is convex • Occlusal 2/3s are flat

Roots• The 3 roots are visible• B bifurcation is at junction between Cervical &

middle 1/3s• Shallow vertical groove in the midline of the B root

trunk • MB & DB roots are narrow & incline to each other

in the apical 1/3 (type trait)• MB root apex is in line with MB cusp tip (type

trait)• The longest L root is visible between the B roots


Lingual aspect 2 cusps of unequal size ML cusp

• Makes 3/5s of MD width of the crown• Prominent & blunt

DL cusp• Rounded, shorter & narrower• Larger than those of 2nd & 3rd max.

molars (type trait)

L groove• Separates L cusps• Terminates midway of L surface

Maxillary permanent 1st molarLingual aspect

M profile is convex except in the flat C 1/3 D profile is entirely convex L surface

• Evenly convex OC• L groove divides L surface into M & D segment• Cusp of Carabelli on M segment (racially variant)

Roots• The 3 roots are visible• Proximal outline of B roots• L root

– Tapered with blunt apex– Shallow vertical depression from CL to 2/3s – L root apex is in line with crown midline (type

trait)


Mesial aspect Maximum MD dimension at the

cervix of the crown ML is higher than MB cusp B cervical 1/3 is strongly convex B outline continues lingually in a

straight line L outline is uniformly convex L HOC is at the midpoint CL is slightly convex occlusally


Mesial aspect Mesial surface

• M MR is marked by several tubercles & supplementary grooves (type trait)

• Contact point is between middle & occlusal 1/3s• Cervical 1/3 is flat or concave• Occlusal 2/3s are convex

Roots• MB & L roots• MB root is broad BL• L root is narrow & Banana-shaped,

curves L then B at the apex• Both MB & L roots project beyond crown profile


Distal aspect DB cusp is more prominent than DL Only small portions of M cusps are

visible (type trait) D MR is shorter & less

prominent than M D MR rarely has tubercles B & L profiles are similar to

those of M aspect CL is nearly straight


Distal aspect Distal surface

• Uniformly convex Roots

• 3 roots visible

• DB root is shorter & narrower than MB root


Occlusal aspect Square or rhomboidal MB & DL angles are acute ML & DB angles are obtuse 1/3 of B surface & ½ of L

are visible B outline: D part is more L

than M part


Occlusal table 2 distinct components

• Trigon– Bears MB, ML & DB cusps

– Tricuspate triangle

• Talon– Bears DL cusp & D MR

– Located DL to the tricuspate triangle

– Well-developed in 1st molar & undergoes reduction in size in 2nd & 3rd molars

Maxillary permanent 1st molarOcclusal table

Cusps in order of decreasing size: ML, MB, DB & DL

M MR is longer & more prominent than D MR

Oblique ridge Major Fossae

• Central fossa– Central pit– B & D grooves – Central groove

• Distal fossa– D pit– DL groove which continues as the L groove


Occlusal table Minor fossae

• M triangular fossa– M pit

– MB & ML supplementary grooves

• D triangular fossa– Distal pit

– DB & DL supplementary grooves


Pulp MD section

• 2 horns, MB is higher

• Pulp chamber, roof & floor

• Canals, narrow

• Canal orifice BL section

• Pulp chamber is wider

• 2 horns of equal height X-section

• 3 canals

Maxillary permanent 2nd molarBuccal aspect (type traits)

Smaller crown size Less prominent DB cusp & narrower

MD Distally inclined B roots

Lingual aspect DL cusp is smaller in width & height L root is narrower MD & slightly D

inclined No cusp of Carabelli?

Maxillary permanent 2nd molar

Mesial aspect Less numerous MR tubercles MB & L roots are less divergent

Distal aspect Smaller D cusps A greater portion of the occlusal

aspect is visible

Maxillary permanent 2nd molar

Occlusal aspect• MB & DL angles are more acute• ML & DB angles are more obtuse• Talon is more reduced in size• More variable pit/groove pattern• More numerous supplementary

groove• Crown is more constricted MD

Pulp Similar to that of 1st molar

Maxillary 3rd molar

Buccal aspect (type traits) Crown is smallest in all dimensions Roots are much short & commonly

fused Shows a pronounced distal

inclinationLingual aspect (type traits)

DL cusp is usually missing L root is commonly fused with the

B roots

Maxillary 3rd molar

Mesial aspect Crown profile is irregular Fused roots

Distal aspect DL cusp is absent More of the occlusal surface is

visible compared with 1st & 2nd

Maxillary 3rd molar

Occlusal aspect (type traits) Triangular or heart-shaped

outline DB cusp is of minimal size Oblique ridge is barely visible Pit/groove pattern is variable Numerous supplementary

grooves

Maxillary 3rd molar

Pulp MD section

• Large MB horn & small DB horn

BL section• MB & L horns are

of equal prominence X- section

• Ovoid• Narrow MD

Maxillary 3rd molar

Anatomic variation

Mandibular permanent molars

Upper & lower molars show progressive reduction posteriorly

(human trait)The 1st to appear of permanent

dentition (6 yrs)Arch traits

2 roots; M & D 4 major cusps & 1 lesser-sized 5th cusp

(in 1st molars) Crowns broader MD than BL The 2 L cusps are of equal size MB & DB cusps are of equal size

Mandibular permanent 1st molar

Buccal aspect Widest MD (type trait) MB, DB & D cusps MB cusp is the widest then DB & D MB & DB are of equal height D cusp is conical located in the DB

corner MB & DB grooves


Buccal aspect M profile

• C 1/3 is straight or concave• Occlusal 2/3s are convex

D profile is entirely convex M & D profiles are convergent cervically CL is similar to that of upper 1st molar

Buccal surface Buccal cervical ridge in C 1/3 MB groove ends halfway DB groove extends most of B surface

length


Buccal surface Roots

• 2 roots; M & D• Widely separated (type trait)• Share a common trunk that has

a shallow vertical depression• Apical half of M root is distally

inclined• D root projects distally without

curvature


Lingual aspect ML & DL cusps

• Of equal size• Higher & more conical than B cusps

Lingual groove Narrower MD than B profile M & D profiles

• Generally convex except in the straight or concave C 1/3

• Convergent cervically


Lingual surface Occlusal 2/3s are convex in both

H & V planes Cervical 1/3 is flat or concave

Roots Vertical shallow depression on

the midline of the root trunk Proximal surfaces of roots are

visible


Mesial aspect ML cusp is slightly higher than MB MR is higher & has mesial marginal groove From buccal cervical ridge, B outline curves

sharply lingually (arch trait) L profile is convex L HOC between middle & occlusal 1/3s M surface is flat or concave in the C 1/3

& convex in the occlusal 2/3s Roots

• Broad BL (type trait)

• Blunt apex

• Proximal root concavity

Mandibular permanent 1st molarDistal aspect

3 cusps• DL, DB & D (order of decreasing size)

• D cusp is L to DB cusp

• DB groove

• D MR is shorter than M & has a distal marginal groove

• 1/2 of B surface is visible

• CL is straight

• Narrower BL than M surface

• Root– Broad BL, but narrower than M root

– Blunt apex

– may have shallow depression


Occlusal aspect Crown is pentagonal (type trait) B profile is longer than L M profile is longer than D B profile

• 3 regions

• DB is the most prominent

• Maximum BL diameter is just D to MB groove (type trait)


Occlusal aspect MB angle is sharp DB angle is rounded M & D profiles are convergent

L (type trait) L profile 2 regions 2/3s of buccal surface are

visible (arch trait) L profile: only occlusal 1/3 is

visible


Occlusal table 5 cusps (type trait) 2L cusps, MB, DB & distal (order of

decreasing size) L cusps are more pointed & conical M & D MRs converge L (type trait) M MR is higher and longer Marginal grooves


Occlusal table Fossae

• Central fossa

• 2 M & D triangular fossae Grooves

• Central

• MB & L terminate in the central pit

• DB (y-shape with MB & L [type trait])

Pits• M, D & central


Pulp MD section

• 2 horns – MB > DB

• Narrow canals BL section

• 2 horns– ML > MB

• 2 canals in M root Transverse section

• Rectangular

Mandibular permanent 2nd molar

Buccal aspect Smaller than 1st but larger than

3rd in all dimensions (type traits) Only 2 B cusps & 1 B groove

(type trait) L cusps are more prominent

from B aspect (type trait) Roots (type traits)

• Much closer together• D inclined


Lingual aspect Crown is shorter OC Little of proximal surfaces is visible M & D profiles are less convergent

cervically

Mesial aspect Root is narrower BL with sharp apex


Distal aspect D cusp is missing (type trait) Less of B surface is visible (type

trait) D root is much narrower BL with

a pointed apex (type trait)


Occlusal aspect (type traits) Crown is rectangular B profile = L in length M profile = D in length Most prominent of B profile

is in the region of the MB cusp Maximum BL dimension is

just M to B groove M cusps are wider MD than D cusps


Occlusal aspect MRs

• Straight BL• Not crossed by marginal grooves

“+” groove pattern More numerous Supplementary

grooves


Pulp Similar to that of 1st BL section

• Usually 2 canals in M root• Sometimes 1 canal in M

root T-section

• M dimension > D

Mandibular 3rd molar

Buccal aspect Highly variable Roots are short, fused & D inclined

Lingual aspect Short crown of highly bulbous

outline Rounded cusps

Mandibular 3rd molarMesial

B & L profiles are highly convex Distance between apices of M cusps is

shorter

Distal Almost entire B surface is visible D root is the narrowest BL & shortest

of all mandibular molars

Pulp is similar to mandibular 2nd molar

Mandibular 3rd molar

Occlusal aspect Ovoid in outline M half is wider BL than D half B & L Profiles converge D Highly restricted occlusal table in

MD & BL dimensions (type trait) 4 narrow conical cusps Highly convex MRs Irregular pit/groove pattern Shorter grooves

Permanent Molar - size & eruption

Tooth Crown height

MD crown diameter

BL crown diameter

Tooth length

Age at eruption

16 or 26 7.5 mm 10.0 mm 11.0 mm 19.5 mm 6 yrs17 or 27 7.0 mm 9.0 mm 11.0 mm 18.0 mm 12 yrs18 or 28 6.5 mm 8.5 mm 10.0 mm 17.5 mm 18+yrs36 or46 7.5 mm 11.0 mm 10.5 mm 21.5 mm 6 yrs37 or47 7.0 mm 10.5 mm 10.5 mm 20.0 mm 12 yrs38 or 48 7.0 mm 10.0 mm 9.5 mm 18.0 mm 18+yrs

Documents

Morphology of Molars