lower premolars

Permanent mandibular premolars

Posterior Permanent Dentitionpremolars and molars

The crown of each posterior tooth has an occlusal surface, bordered distally & mesially by marginal ridges

The occlusal surfaces have two or more cusps

Imagine each cusp as a mountain with sloping areas, or cusp ridges, extending from the top of the mountain

Each shallow, wide depression on the occlusal table is a fossa:

central fossa , is located where the cusp ridges converge in a central point, where the grooves meet

triangular fossa

Sometimes located in the deepest portions of the fossa are occlusal developmental pits.

Each pit is a sharp pinpoint depression where two or more grooves meet.

1

2

3

Permanent PremolarsThere are eight premolars in the

permanent dentition, two in each quadrant.

They are located posterior to the canines & immediately anterior to the molars:so they called transitional tooth

Mandibular First Premolars The 4th tooth from the median line

The 1st post. Tooth in mandible

1) B cusp is long & sharp & the only occluding cusp

2) BL miasurment is similar to canine3) The occlusal surface slopes sharply

lingually in cervical direction4) MB cusp ridge is shorter than DB cusp

ridge5) The tooth has more than one cusp

The mandibular first premolars have a long and well-formed buccal cusp and a small, nonfunctioning lingual cusp.

The lingual cusp may be no larger than the cingulum on some maxillary canines.

The mandibular first premolars are smaller and shorter than the mandibular second premolars.

Buccal aspect Crown is nearly symmetrical bilaterally &

trapezoidal1) Large pointed B cusp,located a little M to

the center of cusp buccally2) M cusp ridge shorter than D cusp ridge3) The contact area almost at the same level

at M & D, a little more than half of distance from cervical line to cusp tip

4) H of C is in the contact area in M,D & in cervical third in B5) B surface of the crown is more convex than Max premolars, especially at cervical & middle thirds

DM

Lingual aspect The crown tapers toward the L…L

measurement MD is less than that buccally1) L cusp is always small,usually shows pointed

tip2) The cervical portion is narrow & convex 3) concavities between the cervical line &

contact areas on L portion of M & D surface4) Characteristic of this surface:ML developmental groove as a line of

demarcation between the MB lobe & the L lobe & extends in to the M fossa of occlusal surface 5) H of C is in middle third

Mesial aspect1) The Crown outline is rhomboidal2) The tip of B cusp is nearly centered over

the root3) The convexity of the outline of L lobe is L

to the outline of root,the surface of the crown presents an overhang above the root trunk in L direction

4) The convexity of L surface curvature is less than B

5) The crest of curvature is near middle third in B & L6) Contact area & M marginal ridge more occlusally than D surface

Distal aspect1) Marginal ridge is higher above the cervix,

does not have the extreme L slope of M marginal ridge

2) There is no DL developmental groove(we can see ML.D.G in M surface)

3) D contact area is broader than M,it centered in the same relation of the crown outline: midway between B & L crests of curvature, midway between cervical line & the tip of B cusp

4) The surface of root D, exhibits more convexity

5) D surface is smaller occ-cervically but broader B-L

6) Contact area more cervically in comparison to M

Occlusal aspect1) Usually Diamond shaped2) Middle B lobe makes up the major bulk of crown3) B ridge is prominent4) MB & DB line angles are prominent but rounded5) The curvature representing contact

areas,immediately L to the B line angle,are relatively broad,specially in D

6) The L cusp is small7) M & D fossa:D fossa more deep than M8) ML developmental groove & depression9) D pit: intersection of central, marginal D, DB

triangular & DL triangular grooves

root

1) One conical root2) Pointed apex3) BL width more than MD4) Convex B & L surface,convex to flat M & D

surface5) The convexity of root in D is more than M6) The root outline is tapered from cervix

ending in a relatively pointed apex in line with the tip of B cusp

Mandibular second premolar erupt distal to the mandibular first

premolars They are the succedaneous replacements

for the primary mandibular second molars

There are two forms of the mandibular second premolar:• Three-cusp type, or tricuspidate form• Two-cusp type, or bicuspidate form

The 5th tooth from the midline Resembles 1st premolar only from B aspect The tooth is larger and better developed

in other aspect Lingual cusps are functional & better

developed The two types differ mainly in occlusal

design Single root Larger & longer root than 1st premolar

Buccal aspect Shorter B cusp Both M & D contact area are broad &

seems to be higher(because of shorter B cusp)

Lingual aspect Lingual lobes are developed to a greater

degree In 3cusp type ML cusp is larger,a groove

between them usually centered over the root

In 2cusp type: DL developmental groove

Mesial aspect Crown & root are wider buccolingually B cusp is not so nearly centered over the

root trunk The marginal ridge is at right angle to the

long axis No ML developmental groove

Distal aspect D Marginal ridge is at a lower level than MThe crown of all posterior teeth(maxillary

& mandibular)are tipped D to the long axis of roots…it is an important observation in study of occlusion

Occlusal aspect3cusps type:

Appears square shapeB cusp is the largest,ML cusp is the next,DL is

the smallestDeep Developmental grooves converge in a

central pit, form a Y shape on the occlusal surface

2cusps typeRound occlusal shapeML & DL line angles are roundedOne well developed L cusp is directly opposite

the B cusp

root The root is broader MD than 1st premolar The apex is more blunt & the root is

Longer Much less convergence toward L than 1st

premolar

Crown Length Root length MD diameter BL diameter Eruption

8.5 14 7 7.5 10-12 22.5

Crown Length Root length MD diameter BL diameter Eruption

8 14.5 7 8 11-12

22.5