Morphology Of Molars

MORPHOLOGY OF PERMANENT MOLARS Dental Anatomy Dent 201 Summer semester 2005/20006

Permanent Molars ❧Class traits ● ● ●

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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) ●

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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 ●

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MB & DB cusps are of equal height MB is wider Separated by B groove • Terminates halfway

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Slopes of DB are steeper Tip of the ML cusp between B cusps

Maxillary permanent 1st molar ❧ Buccal aspect ●

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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

Maxillary permanent 1st molar ❧ Buccal aspect ●

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

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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

Maxillary permanent 1st molar ❧ Lingual aspect ● ●

2 cusps of unequal size ML cusp • Makes 3/5s of MD width of the crown • Prominent & blunt

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DL cusp • Rounded, shorter & narrower • Larger than those of 2nd & 3rd max. molars (type trait)

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

Maxillary permanent 1st molar ❧ Lingual 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)

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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)

Maxillary permanent 1st molar ❧ Mesial aspect ●

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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

Maxillary permanent 1st molar ❧ 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

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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

Maxillary permanent 1st molar ❧ Distal aspect ● ●

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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

Maxillary permanent 1st molar ❧Distal aspect ●

Distal surface • Uniformly convex

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Roots • 3 roots visible • DB root is shorter & narrower than MB root

Maxillary permanent 1st molar ❧ Occlusal aspect ● ● ● ●

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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

Maxillary permanent 1st molar ❧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 molar ❧ Occlusal table ●

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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

Maxillary permanent 1st molar ❧Occlusal table ●

Minor fossae • M triangular fossa – M pit – MB & ML supplementary grooves

• D triangular fossa – Distal pit – DB & DL supplementary grooves

Maxillary permanent 1st molar ❧ Pulp ●

MD section • 2 horns, MB is higher • Pulp chamber, roof & floor • Canals, narrow • Canal orifice

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BL section • Pulp chamber is wider • 2 horns of equal height

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X-section • 3 canals

Maxillary permanent 2nd molar ❧Buccal aspect (type traits) ● ●

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Smaller crown size Less prominent DB cusp & narrower MD Distally inclined B roots

❧Lingual aspect ● ●

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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) ● ●

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Crown is smallest in all dimensions Roots are much short & commonly fused Shows a pronounced distal inclination

❧Lingual aspect (type traits) ● ●

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

Maxillary 3 molar rd

❧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) ●

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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

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BL section • MB & L horns are of equal prominence

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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 ● ●

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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 ● ● ● ● ●

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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

Mandibular permanent 1st molar ❧ Buccal aspect ●

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

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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

Mandibular permanent 1st molar ❧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

Mandibular permanent 1st molar ❧Lingual aspect ●

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

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Lingual groove Narrower MD than B profile M & D profiles • Generally convex except in the straight or concave C 1/3 • Convergent cervically

Mandibular permanent 1st molar ❧Lingual surface ●

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Occlusal 2/3s are convex in both H & V planes Cervical 1/3 is flat or concave

❧Roots ●

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Vertical shallow depression on the midline of the root trunk Proximal surfaces of roots are visible

Mandibular permanent 1st molar ❧ Mesial aspect ● ● ●

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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 molar ❧ Distal 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

Mandibular permanent 1st molar ❧ 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)

Mandibular permanent 1st molar ❧Occlusal aspect ● ● ●

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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

Mandibular permanent 1st molar ❧ Occlusal table ● ●

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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

Mandibular permanent 1st molar ❧ Occlusal table ●

Fossae • Central fossa • 2 M & D triangular fossae

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Grooves • Central • MB & L terminate in the central pit • DB (y-shape with MB & L [type trait])

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Pits • M, D & central

Mandibular permanent 1st molar ❧ 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 ●

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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

Mandibular permanent 2nd molar ❧ 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

Mandibular permanent 2nd molar ❧Distal aspect ● ●

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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)

Mandibular permanent 2nd molar ❧ Occlusal aspect (type traits) ● ● ● ●

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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

Mandibular permanent 2nd molar ❧Occlusal aspect ●

MRs • Straight BL • Not crossed by marginal grooves

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“+” groove pattern More numerous Supplementary grooves

Mandibular permanent 2nd molar ❧Pulp ● ●

Similar to that of 1st BL section • Usually 2 canals in M root • Sometimes 1 canal in M root

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T-section • M dimension > D

Mandibular 3rd molar ❧Buccal aspect ● ●

Highly variable Roots are short, fused & D inclined

❧Lingual aspect ●

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Short crown of highly bulbous outline Rounded cusps

Mandibular 3rd molar ❧ Mesial ● ●

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 ● ● ● ●

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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

16 or 26

7.5 mm 7.0 mm 6.5 mm 7.5 mm 7.0 mm 7.0 mm

17 or 27 18 or 28 36 or46 37 or47 38 or 48

MD crown BL crown diameter diameter

10.0 mm 9.0 mm 8.5 mm 11.0 mm 10.5 mm 10.0 mm

11.0 mm 11.0 mm 10.0 mm 10.5 mm 10.5 mm 9.5 mm

Tooth length

Age at eruption

19.5 mm 18.0 mm 17.5 mm 21.5 mm 20.0 mm 18.0 mm

6 yrs 12 yrs 18+yrs 6 yrs 12 yrs 18+yrs