morphology of permanent first premolar

1. PERMANENT MANDIBULAR FIRST
PREMOLAR
Dr jameel kifayatullah
Kcd peshawar

2. PERMANENT MANDIBULAR FIRST PREMOLAR
• buccolingual and mesiodistal crown dimensions
approximately equal
• When viewed from proximal the mandibular
premolar crown profile tilts towards the lingual
• The two mandibular premolars are transitional
teeth with the first premolar reflecting the
transition from the canine and the second
premolar showing the change towards the molars
• First mandibular premolar Diminutive lingual
cusp nonfunctional so that its morphology and
role in mastication parallel those of the canine
• The slope of marginal ridges in first premolar
similar to that of anterior teeth

3. General characteristics
• Fourth tooth from the midline
• Succedaneous tooth replacing the deciduous
first molar
• Numbering system: right:#28
Left #21
• FDI RIGHT :44
• LEFT :34

4. General form and function
• Two cusp with buccal cusp only functional
thus resembling canine
• Diamond shaped outline from occlusal aspect
resembling canine
• Facial or lingual aspects: pentagonal form
• Proximal surfaces: rhomboidal in outline
• Closer in form and masticatory function to a
canine

5. Developmental table
• Inititiation of calcification: 1.75-2 years
• Completion of enamel: 5-6 years
• Eruption: 10-11 years
• Root completion: 12-13 years

6. Buccal aspect:
• pentagonal outline
• Buccal surface convex occlusogingivally and
mesiodistally
• Occlusocervical dimension shorter than that
of anterior teeth

7. Buccal aspect
• Mesial Margin- concave from contact area to
cervical line
• Height of contour is in the middle third
• Distal Margin- concave from contact area to
cervical line, Only a little shorter than mesial
margin
• Height of contour is in the middle third
• Cervical outline- Cervical line presents an even
slightly convex curve towards the apex
• Depth of curvature less than anterior teeth

8. Buccal aspect
• Occlusal outline: Pointed buccal cusp tip dividing the occlusal
outline into mesio- occlusal slopes and disto-occlusal slopes.
• shorter mesio-occlusal slope therefore cusp tip offset towards
mesial
• Other considerations: prominent buccal ridge
Mesiobuccal and distobuccal developmental
depressions
No imbrications lines
• Contact areas located approximately at same level in the middle
third
• UNIQUE FEATURE: the marginal ridges are at same level
• Buccal Height Of Contour: Cervical third

9. BUCCAL SURFACE

10. LINGUAL SURFACE

11. LINGUAL ASPECT
• General considerations-
• Lacks prominent occlusocervical ridge
• Convex in all directions
• Buccal half of occlusal table visible from this
aspect(small Lingual cusp and inclination of
crown towards lingual)
Lingual cusp dimensions less than buccal cusp
• Lingual surface narrower mesiodistally

12. LINGUAL ASPECT
• Mesial and distal margins-Similar to buccal surface but much
shorter
• Cervical Outline- CEJ slightly convex towards apical
• Occlusal outline- lingual cusp tip short but sharp
Disto-occlusal slope longer than the mesio-occlusal
slope thus cusp tip offset to mesial
portion of crown distal to transverse ridge larger
than mesial (both cusp tips offset mesially)
• Other considerations- lingual Height of contour in middle third
• Landmark feature: Mesiolingual
developmental groove

14. Mesial aspect
General considerations- rhomboidal in form
Buccal margin- convex with height of contour in cervical third
Buccal margin inclined towards lingual
Lingual margin- less convex and much shorter than buccal outline
Height of contour in middle third
Cervical outline- Cervical line curved slightly towards the occlusal
Occlusal outline: Buccal portion of transverse ridge sloping at 45
degree angle
Buccal cusp tip located over centre of root(lingual
inclination)
Other considerations: mesiolingual developmental groove
Contact area located towards buccal in middle
third
Ovoid shape
Height of contour –Middle third

15. MESIAL SURFACE

16. Distal aspect
• similar to the mesial surface with some
exceptions:
• No distolingual developmental groove ,there
is distal marginal groove
• Shorter occlusocervically but wider
buccolingually than mesial surface
• Contact area ovoid occupying a broader area
• Distal marginal ridge not steep towards
lingual

17. Distal surface

18. Occlusal aspect
• General considerations- rhomboidal crown
profile Or DIAMOND Shaped
• Notch in mesial outline at mesiolingual
developmental groove
• Distal portion of tooth larger(mesial offset of
both cusp tips)

19. OCCLUSAL SURFACE
• Buccal outline- uniformly convex, rounder
MB and DB line angles,prominent buccal ridge
• Lingual outline: convex,shorter than mesial
,mesially ending near mesiolingual
developmental groove
• Distal outline- More Regularly convex than
mesial outline

20. Occlusal surface
Boundaries
• mesial and distal marginal ridges proximally,
• buccal and lingual boundaries are formed by
the mesial and distal cusp ridges of both
cusps

21. Occlusal surface
Components of occlusal surface
A) Cusps
B) Transverse ridge-
C) Marginal ridges
D) Fossae
E) Pits and grooves

22. OCCLUSAL SURFACE
Cusps TWO CUSPS –buccal and lingual
Buccal cusp- larger and functional cusp
offset mesially
4 CUSP RIDGES And 4 inclined
planes (functional)
• Lingual cusp : Non functional cusp, smaller,
offset to mesial, 4 cusp ridges,4 inclined
planes(non functional)

23. OCCLUSAL SURFACE
• Transverse ridge- buccal triangular
ridge+lingual triangular ridge
• Marginal ridges- mesial marginal ridge slope
from buccal to lingual at a 45 degree angle
• Distal marginal ridge longer ,not as quite steep
slope towards lingual

24. Occlusal surface
Fossae:
• Two irregular depressions mesial and distal
fossae
• Mesial fossa linear in shape,distal fossa larger
and circular

25. Occlusal surface
Pits and grooves
MESIAL PIT: Location: distal to mesial marginal ridge at
midpoint buccolingually on occlusal surface
• point of union of 3 grooves 1)central groove,2) MB
triangular groove3)Mesiolingual developmental groove
• Distal pit:Location: mesial to distal marginal ridge,
• It is the junction of 4 primary grooves
1) central groove 2)Distal marginal groove 3)DL
triangular groove 4)Distobuccal triangular groove

26. Occlusal surface

27. ROOT
single root
fairly straight
outline tapers from cervical line to sharp apex
Root length is slightly less than that of
mandibular second premolar root
Root length =14 mm

28. ROOT
Wider buccolingually than MD,buccal and lingual
surface convex
Mesial and distal surface slightly covex to flat
Root concavities occasional
Midroot Cross section:ovoid outline
wider BL than MD
wider at the buccal than
at lingual