Understanding Maxillary Premolars: Permanent First and Second Premolars

1. “Permanent”Maxillary Premolars First Premolars

2. General Characteristics: • Arch position: 4th tooth from midline • Between the canine and 2nd premolar • Universal #5 and 12

3. General Form • Proximal geometric form is trapezoidal • Occlusally, resembles 6-sided figure • Facially, similar to canine (5-sided)

4. Form & Functions: • Two fairly equal cusps: facial and lingual (F>L) • Assists canine in tearing and piercing • Presence of an occlusal table • Essentially a “grinding” tooth

5. Development Timeline: • Initial calcification: 1 1/2 to 1 3/4 years • Enamel completed: 5 - 6 years • Eruption: 10 - 11 years • Root completed: 12 - 13 years

6. Facial View • Closely resembles canine • Prominent buccal cusp ridge with depressions on either side • Facial HOC at cervical third • Occl-cerv dimension greater than maxillary 2nd premolar #12

7. Facial view, mesial outline: • Mesial HOC at junction of occlusal-middle thirds • Outline cervical to contact area slightly concave

8. Facial view, distal outline: • Similar to mesial outline • HOC slightly more cervical than mesial • Less cervical concavity

9. Facial view, occlusal outline: • Similar to canine except: • Cusp tip not as prominent • Cusp tip located just distal to midline of root* • Longer MB cusp ridge* • Shorter DB cusp ridge* *unique

10. Lingual View • Lingual narrower M-D than facial • Lingual cusp shorter than facial (shortest of maxillary premolar cusps) • Lingual cusp offset to mesial • Lingual HOC at middle third

11. Mesial View • Trapezoidal geometric form • F and L cusps centered over root trunk • Strong mesial marginal groove visible

12. Mesial view... • Mesial concavity from root trunk to cervical portion of crown* • Mesial contact area facial to F-L midline

13. Distal View • Similar to mesial view except: • Shorter O-C than mesial • Distal marginal ridge more cervical • More of occlusal surface visible* • No distinct distal concavity • Distal contact area slightly more cervical and facial than mesial

14. Occlusal View • Outline is hexagonal • Wider F-L than M-D • Outline tapers towards lingual • Lingual cusp offset to mesial • Mesial marginal ridge shorter than distal marginal ridge

15. Occlusal view... • Mesial outline indented with mesial marginal groove • M and D pits well-separated • Less secondary grooves than 2nd maxillary premolar • Mesial contact area more lingual than distal contact area

16. Occlusal view... • DB cusp ridge-distal marginal ridge angle is acute • MB cusp ridge-mesial marginal ridge angle is 90o

17. Root Form • Single root (Type I) • Distinct mesial concavity • Two root canals: F and L • Cervical cross-section: kidney (bean) shape

18. Root form: • Bifurcated root (Type II) • Most common form • Short root trunk • Two roots: F and L, almost equal lengths (F>L) • Mid-root cross section: 2 roots • Cervical cross-section is also bean-shaped

19. Root form: • Laminated root (Type III) • Resembles Type II except: • Longer root trunk • F and L roots joined by lamination • Mid-root cross-section: hour-glass shape • Cervical cross-section: bean-shaped

20. Root variations: • Trifurcation possible • 2 buccal roots and 1 lingual • Pulp canals: separate or connected • 2 pulp horns

21. How To Tell Right From Left: • Mesial concavity* • Lingual cusp tipped mesially* • Mesial marginal groove • MB cusp ridge longer than DB*

22. Maxillary Second Premolar

23. General Characteristics: • Arch position: 5th tooth from midline • Universal #4 and #13

24. Differences between 1st and 2nd: • Crown dimensions of 2nd smaller than 1st • 1st more angular, 2nd more rounded* • F and L cusps more equal in height with 2nd*

25. Differences… • No mesial concavity or mesial marginal groove with 2nd* • 2nd normally single rooted • M and D pits closer together in 2nd* (shorter central groove) • More supplemental grooves in 2nd*

26. Developmental Timeline: • Initial calcification: 2 - 2 1/4 years • Enamel completed: 6 - 7 years • Eruption: 11 - 12 years • Root completed: 12 - 14 years

27. Facial View • Similar to 1st except: • Buccal cusp of 2nd not as long or pointed (buccal cusp of 1st longest of the maxillary premolar cusps) • Cusp tip mesial to root midline • MB cusp slope shorter than DB* • M and D contact areas slightly more cervical than 1st

28. Lingual View • Similar to 1st • Lingual cusp longer (nearly equal to facial cusp) • Lingual cusp slightly offset to mesial • Less convergence from facial to lingual

29. Mesial View • Similar to 1st except: • F and L cusps more equal height* • No mesial concavity* • Usually no mesial marginal groove • Mesial contact area more cervical

30. Distal View • Similar to 1st except: • F and L cusps more equal height • Distal contact area more cervical • Distal root depression more pronounced than mesial

31. Occlusal View • Line angles more rounded than 1st* • Central groove shorter* • M and D pits closer together* • More supplemental anatomy* • M and D halves appear more symmetrical (most symmetrical of the premolars)

32. Root Form • Usually single rooted (bifurcation rare but possible) • No deep mesial depression* • Root cross-section is ovoid

33. How To Tell Right From Left: • Lingual cusp tipped mesially* • MB cusp ridge shorter than DB • Root apex deviation usually towards distal

34. How To Tell 1st from 2nd: • 1st usually bifurcated roots* • Occlusal outline of 1st more angular, more rounded with 2nd* • 1st has mesial concavity*

35. 1st from 2nd... • Central groove of 1st longer • M and D pits of 1st further apart* • MB cusp ridge of 1st longer than DB (opposite with 2nd) • Less supplemental grooves in 1st • Less lingual taper (convergence) in 2nd

42. Tooth ID Test

44. Circle starting number

46. Questions???