morphology of premolars

Morphology of Premolars

Oral HistologyDent 205

Summer semester2005/2006

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


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


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


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


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


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


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


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


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


Pulp Cigar shaped X-section at cervix Pulp horns of almost equal height Usually a single pulp canal


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


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


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


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


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


Pulp ML section

• Similar to that of canine BL section

• A large B horn &

a small L horn X section

• Ovoid


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 & L 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


Pulp BL section

• Pulp chamber is wider

• Pulp horns are of

equal height X – section


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

morphology of premolars

Documents

premolarl buccalaspectq

triangular ridge

oblique ridge

transverse ridge

triangular fossa

supplemental groove

developmental groove

ridgesor depressions