Comparative Assessment of Cuspal Deflection in Premolars ...
Morphology of Premolars
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Transcript of Morphology of Premolars
Morphology of Premolars
Dr. Firas Alsoleihat, BDS, PhD Dental Morphology
Department of Conservative Dentistry
IntroductionPosterior (cheek) teethPremolars
Eruption 10 – 12 yearsPremolars/bicuspids
Although some havemore than 2 cusps
Class traits At least 2 cusps Single buccal cusp
with one or more lingual cusps
Molars must have at least 2 buccal cusps
Landmarks related to posterior teeth
Cusp ridgeTriangular ridgeTransverse ridgeOblique ridgePit Developmental grooveSupplemental grooveTriangular fossaCentral fossa
Maxillary premolars
Arch traits 1st & 2nd are much more a like while
they are different in mandibular Have 2 major cusps
approximately
equal in size & prominence Wider BL than MD
while in mandibular BL = MD
Maxillary premolars
Arch traits (cont’d) Slight lingual inclination of the
crown while mandibular have strongly lingually inclined crowns
In maxillary, lingual Height Of Contour (HOC) is in the middle 1/3, while it is in the occlusal 1/3 in mandibular
Maxillary 1st premolarBuccal aspect
Similar to that of max. canine• slightly smaller
Similar to that of 2nd premolar• slightly larger
Tip of buccal cusp is distal
to the MD midline Sloping cusp ridges
• M is long & straight
• D is short & convex
Buccal aspect Proximal outlines and HOCs
• M is slightly concave with HOC
just occlusal to the halfway point
• D is straight, HOC is more
occlusally located than in M Overhanging MO & DO angles
(type traits) A small part of the M margin of
the L cusp can occasionally be seen
Maxillary 1st premolar
Buccal aspect 3 lobes MB & DB depressions
and labial ridge CL has a slight convexity
toward root apex Root is conical similar to
that of canine but smaller
Maxillary 1st premolar
Lingual aspect Entire buccal outline is
visible (type trait) L cusp tip is mesial to the
midline of the crown No protuberances, ridges or
depressions Root
• 2 apices are visible
• Interradicular groove is visible
Maxillary 1st premolar
Mesial aspect Buccal cusp is higher than lingual Triangular ridges incline at 45 degrees Mesial Marginal ridge
• Prominent• Mesial marginal groove just lingual to the
midportion Buccal HOC within cervical 1/3 from
which a slight lingual inclination toward cusp apex
Lingual outline is convex with HOC within middle 1/3
Cervical line CL is convex toward occlusal
Maxillary 1st premolar
Mesial aspect Mesial interradicular groove
• From the cervical 1/3 down to root bifurcation
• In line with mesial marginal groove Occlusal table is centered over root
trunk
(arch trait) Root(s)
• Commonly 2 roots
• bifurcate at the junction between middle & apical 1/3s
Maxillary 1st premolar
Distal aspect Similar to mesial aspect except
• More of the occlusal surface may
be seen• No marginal groove• No concavity in the cervical 1/3• Distal interradicular is shallower
Maxillary 1st premolar
Occlusal aspect Hexagonal (type trait) Buccal profile is inverted V Sharp MB & DB (type trait) Slightly convergent M & D profile
(type trait) L profile is strongly convex Buccal ridge & depressions are visible Occlusal table formed by cusp &
marginal ridges Apex of lingual cusp is mesial to the
midline
Maxillary 1st premolar
Occlusal aspect Triangular ridges
• B & L are separated by the central groove• Buccal flanked by supplemental grooves on
either sides Central groove terminates M & D in Triangular fossae
• Bounded by MR & B/L Triangular ridges• M is larger & deeper• Each fossa contains
– A pit– B & L grooves (MB, ML, DB & DL)
Mesial MR is shorter & interrupterd by marginal groove
Maxillary 1st premolar
Pulp In X-section at cervix
• Kidney shaped• Wide BL & narrow MD
In BL section• 2 pulp horns • Buccal is larger
In MD section• Similar to that of canine
Maxillary 1st premolar
Buccal aspect Similar to maxillary 1st premolar Type traits
• Smaller in breadth & height
• MO & DO angles are less prominent
• Buccal ridge & depressions are seldom seen
Lingual aspect Buccal profile is seldom seen
because B & L cusps are identical in dimensions
Maxillary 2nd premolar15
14
14
15
Mesial aspect B & L cusps are equal in height No mesial marginal groove No concavity in the crown
portion
of the mesial surface A single root
Distal aspect B & L cusps are equal in height A singe root
Maxillary 2nd premolar
15
14
14
15
Occlusal aspect Ovoid rather than hexagonal Less convergence of M & D outlines Because B cusp very nearly = L in MD
width More rounded MB & DB corners Apex of L cusp is in the midline Shorter occlusal groove More numerous supplemental groove No mesial marginal grooves
Maxillary 2nd premolar
Pulp Cigar shaped X-section at cervix Pulp horns of almost equal height Usually a single pulp canal
Maxillary 2nd premolar
Chronology
Maxillary first premolar First evidence of
calcification:1.5-1.75yr
Enamel completed:5-6yr
Eruption:10-11yr
Root completed:12-13yr
Maxillary second premolar
First evidence of calcification:2-1.25yr
Enamel completed:6-7yr
Eruption:10-12yr
Root completed:12-14yr
Buccal aspect Long pointed buccal cusp in the
occlusal profile Mesial cusp ridge is shorter than distal Cusp tip is a little mesial to the tooth
midline HOCs are at the same level just
occlusal to the halfway of the crown M & D outlines are markedly converging CL is flat MD compared to that of canine Buccal ridge & depressions Root is conical with pointed apex
Mandibular 1st premolar
Lingual aspect Entire buccal profile and occlusal surface
are visible (type trait) Occlusal surface, buccal triangular ridge
and marginal ridges tilt lingually & cervically in relation to the long axis of the tooth
Buccal triangular ridge crosses midportion of the occlusal surface
Lingual cusp is a minor elevation in height & pointed cone in shape
• It may be centric or eccentric in relation with buccal cusp
Root is narrower from lingual aspect & has a blunt apex
Mandibular 1st premolar
Mesial aspect Occlusal plane tilted lingually
& cervically Transverse ridge that may or may
not be separated by central groove ML groove: MR with ML cusp ridge
(type trait) Buccal profile shows highly lingual
inclination Lingual profile is straight & then
convex up to the cusp tip
Mandibular 1st premolar
Mesial aspect Tip of lingual cusp is in line with
L outline of the root Lingual HOC within occlusal 1/3 M contact area is in line with apex
of B cusp Root is broad BL
Distal aspect D MR is more prominent & less L & C
inclined No DL groove Contact area is more extensive
Mandibular 1st premolar
Occlusal aspect Diamond in shape Inverted V shaped B profile M & D profiles converge
lingually D profile is more convex L profile is ½ MD length of B
profile 2/3 of buccal surface with ridge
& depressions are visible
Mandibular 1st premolar
Occlusal aspect Occlusal table is triangular Tip of B cusp is near the midline
of the crown ML cusp ridge with MR is straight DL cusp ridge with MR is convex M MR is shorter & less prominent
with ML groove M & D fossae, each contains
• A pit• A groove extending BL parallel to MR• M contains ML groove running in a
ML direction from M pit
Mandibular 1st premolar
Pulp ML section
• Similar to that of canine BL section
• A large B horn &
a small L horn X section
• Ovoid
Mandibular 1st premolar
Buccal aspect Similar to Mandibular 1st premolar
Lingual aspect MD diameter = that from B aspect (type
trait) Occlusal surface cannot be seen (type
trait) Occlusal plane is perpendicular to tooth
axis 2 lingual cusps (most commonly)
• ML – major, 2/3 MD diameter, same height as B
• DL – minor Lingual groove
Mandibular 2nd premolar 45
44
44
45
Mesial aspect Triangular ridges of B & ML
cusps don’t form a continuous crest
Distal aspect Both lingual cusps are seen
Mandibular 2nd premolar 45
44
44
45
Occlusal aspect Square profile (type trait) M & D profiles are parallel > ½ B surface is visible B ridge is less prominent than
that of mandibular 1st premolar (type trait)
M & D MRs are equal in length
Mandibular 2nd premolar
Occlusal view Grooves (Y-shape meet at the
central pit)• M separates B & ML triangular ridges
– runs obliquely
• L separates lingual cusps
• D separates B & DL triangular ridges M & D triangular fossae
each contains• A pit
• MB & DB grooves
Mandibular 2nd premolar
Pulp BL section
• Pulp chamber is wider
• Pulp horns are of
equal height X – section
Mandibular 2nd premolar
chronology
Mandibular First Premolar
First evidence of calcification:
1.75-2yr
Enamel completed:
5-6yr
Eruption:10-12yr
Root completed:
12-13yr
Mandibuar Second Premolar
First evidence of calcification:
2.25-2.5yr
Enamel completed:
6-7yr
Eruption:11-12yr
Root completed:
13-14yr
Premolars – size & eruption
ToothCrown height
MD crown diameter
BL crown diameter
Tooth length
Age at eruption
14
248.5 mm 7.0 mm 9.0 mm 23.5 mm 9 yrs
15
258.5 mm 7.0 mm 9.0 mm 22.5 mm 10 yrs
34
448.5 mm 7.0 mm 7.5 mm 22.5 mm 9 yrs
35
458.0 mm 7.0 mm 8.0 mm 22.5 mm 10 yrs
Curves of occlusion
Curve of SpeeCurve of WilsonSphere of Monson
Molar Occlusal relationship
Angle’s Class IAngle’s Class IIAngle’s Class III
Arch Occlusal
relationship