Morphology of Molars - Dental Anatomy
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Transcript of Morphology of Molars - Dental Anatomy
MORPHOLOGYOF
PERMANENT MOLARSDental Anatomy & OcclusionDental Anatomy & Occlusion
Dent 202Dent 202
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
Maxillary permanent 1st molarBuccal 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
Maxillary permanent 1st molarBuccal 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
Maxillary permanent 1st molarLingual 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)
Maxillary permanent 1st molar
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
Maxillary permanent 1st molarMesial 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
Maxillary permanent 1st molarDistal 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
Maxillary permanent 1st molar
Distal aspect Distal surface
• Uniformly convex Roots
• 3 roots visible• DB root is shorter &
narrower than MB root
Maxillary permanent 1st molar
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
Maxillary permanent 1st molarOcclusal 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
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
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 molarOcclusal 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 molarsUpper & 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
Mandibular permanent 1st molar
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
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
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 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
Mandibular permanent 1st molarMesial 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
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 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 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
Grooves• Central• MB & L terminate in the
central pit• DB (y-shape with MB & L
[type trait]) 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 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
cervicallyMesial aspect
Root is narrower BL with sharp apex
Mandibular permanent 2nd molar
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)
Mandibular permanent 2nd molar
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
Mandibular permanent 2nd molar
Occlusal aspect MRs
• Straight BL• Not crossed by marginal grooves
“+” 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 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
shorterDistal
Almost entire B surface is visible D root is the narrowest BL & shortest
of all mandibular molarsPulp is similar to mandibular 2nd molar
Mandibular 3rd molarOcclusal 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