Mandibular Premolars

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Mandibular Premolars

  1. 1. AnatomyAnatomy of Mandibularof Mandibular PremolarsPremolars Howard Chi, D.M.D.
  2. 2. Learning ObjectivesLearning Objectives Anatomy of the mandibular premolars
  3. 3. Type Traits Of MandibularType Traits Of Mandibular PremolarsPremolars 1. A 2-cusp type with 1 lingual cusp 2. A 3-cusp type with 2 lingual cusps
  4. 4. Distinguishing Characteristics OfDistinguishing Characteristics Of Mandibular PremolarsMandibular Premolars Generally speaking : 1. The mand. 1st premolar has a longer crown and a shorter root than the 2nd premolar 2. The mand. 1st premolar is longer overall than the 2nd 2nd 1st
  5. 5. Buccal Aspect OfBuccal Aspect Of Mandibular PremolarsMandibular Premolars 1. Crown Shape: (roughly pentagonal)  1st: Nearly symmetrical except for a shorter mesial cusp ridge and a distal bulge of the crown
  6. 6. Buccal Aspect OfBuccal Aspect Of Mandibular PremolarsMandibular Premolars 1. Crown Shape: (roughly pentagonal) 2nd premolar: Buccal cusp is less pointed and cusp slopes are less steep than on the mandibular 1st premolar 2nd 1st
  7. 7. 2nd 1st Buccal AspectBuccal Aspect 2. Notches on Cusp Ridges:  Notches often seen on mesiobuccal cusp ridge in mandibular 1st premolars  Notches often seen on distobuccal cusp ridge in mandibluar 2nd premolars
  8. 8. Buccal AspectBuccal Aspect 3. Cervical Lines: The cervical line of the mandibular 1st premolar is more rounded mesiodistally, while that of the 2nd premolar is more flat 2nd 1st
  9. 9. Buccal AspectBuccal Aspect 4. Contact Areas - Mesial: 1st and 2nd premolar - near junction of occlusal and middle third
  10. 10. Buccal AspectBuccal Aspect 5. Contact Areas - Distal: 1st premolar distal contact area is more OCCLUSAL than the mesial contact area (an exception to the rule)
  11. 11. Buccal AspectBuccal Aspect 6. Contact Areas - Distal: 2nd premolar has a distal contact located more cervical than the mesial contact area, as is usually the case with posterior teeth
  12. 12. Lingual Aspect Of MandibularLingual Aspect Of Mandibular PremolarsPremolars 1. Crown Shape: Mandibular first premolar crown tapers (converges) to the lingual (narrower on lingual side that buccal)
  13. 13. Lingual Aspect Of MandibularLingual Aspect Of Mandibular PremolarsPremolars 1. Crown Shape:  Mandibular 2nd premolar with 1 lingual cusp, crown tapers to lingual  Mandibular 2nd premolar with 2 lingual cusps, crown is as wide or wider mesiodistally than the buccal
  14. 14. Lingual AspectLingual Aspect 2. Cusp Size and Shape:  Mandibular 1st premolar lingual cusp is small and pointed  Most of the occlusal surface can be seen from this aspect M D
  15. 15. Lingual AspectLingual Aspect 2. Cusp Size and Shape:  Mandibular 2nd premolar with 1 lingual cusp:  Lingual cusp is smaller than buccal cusp, but larger than lingual cusp of 1st premolar M D
  16. 16. 2. Cusp Size and Shape:  Mandibular 2nd premolar with 2 lingual cusps:  ML cusp is larger than the DL cusp, with the L groove between them and onto the lingual crown surface ML DL M D Lingual AspectLingual Aspect
  17. 17. Lingual AspectLingual Aspect 3. Marginal Ridges: Mandibular 1st premolar: Only tooth in the mouth where the mesial marginal ridge is more apical than the distal marginal ridge M D
  18. 18. Lingual AspectLingual Aspect 3. Marginal Ridges: Mandibular 2nd premolar: Mesial marginal ridge is more occlusal than the distal marginal ridge (as found in all other teeth) M D
  19. 19. Lingual AspectLingual Aspect 4. Mesiolingual Groove: Frequently seen on Mandibular 1st premolar only
  20. 20. Proximal Aspect Of MandibularProximal Aspect Of Mandibular PremolarsPremolars 1. Crown Shape - Rhomboid: The crowns of both premolars tilt lingually, but the mandibular 1st premolar tilts more lingually than the mandibular 2nd premolar Mesial View
  21. 21. Proximal Aspect Of MandibularProximal Aspect Of Mandibular PremolarsPremolars 1. Crown Shape - Rhomboid: In both premolars, the lingual cusps are shorter than the buccal cusps Mesial View
  22. 22. Proximal AspectProximal Aspect 2. Mesiolingual Groove:  Often present on Mandibular 1st premolar between the mesial marginal ridge and the mesial slope of the lingual cusp  Not present on Mandibular 2nd premolars
  23. 23. Proximal AspectProximal Aspect 3. Height of Contour: Mandibular 1st premolar Buccal = cervical 1/3 Lingual = middle 1/3
  24. 24. Proximal AspectProximal Aspect 3. Height of Contour: Mandibular 2nd premolar Buccal = junction of cervical and middle 1/3 Lingual = middle 1/3
  25. 25. Proximal AspectProximal Aspect 4. Cervical Lines: Both premolars have greater curve on the mesial than the distal Mesial Distal
  26. 26. Proximal AspectProximal Aspect 5. Root (proximal): Both premolars generally consist of one root The mandibular 1st premolar occasionally will have a furcated root
  27. 27. Proximal AspectProximal Aspect 6. Root Depressions: Mandibular 1st premolar: Have a shallow root depression in the apical and middle thirds of both mesial and distal root surfaces Mesial Distal
  28. 28. Proximal AspectProximal Aspect 6. Root Depressions: Mandibular 2nd premolar: Have a distal root depression in the middle third of the root, but NO mesial depression Mesial Distal
  29. 29. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 1. Outline: – Have much variation in occlusal morphology – Outline is not symmetrical (more bulky on the distal) DM
  30. 30. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 1. Outline: – Often appears as if the mesial side has been pushed inward (mesiolingual corner) DM
  31. 31. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 1. Outline: – Tip of the buccal cusp is near the center from occlusal view – Lacks a prominent buccal ridge – Cusp ridges are nearly straight lines DM
  32. 32. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 1. Outline: – Crown is somewhat diamond shaped converging lingually – Shape of crown is asymmetrical DM
  33. 33. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 1. Outline: – Mesial and distal marginal ridges may converge lingually
  34. 34. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 2. Ridges, Fossae, Grooves: – Due to size of cusp, the buccal triangular ridge is long – Joins the shorter lingual triangular ridge – Often may meet smoothly and form a uninterrupted transverse ridge
  35. 35. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 2. Ridges, Fossae, Grooves: – The transverse ridge may be crossed by a shallow central groove extending from mesial to distal fossa – This is rare
  36. 36. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 2. Ridges, Fossae, Grooves: – The grooves of the first premolar are fewer in number, but may be deeper than those of the second premolar (just like the maxillary)
  37. 37. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular First PremolarFirst Premolar 2. Ridges, Fossae, Grooves: – Possess a mesial and distal fossa – Both are circular, not triangular – Both possess pits – Distal fossa is usually larger and/or deeper D
  38. 38. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 1. Outline - Two-cusp version: – Crown is round or oval shaped with a square occlusal table
  39. 39. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 1. Outline - Two-cusp version: – There is slightly more bulk in the mesial half buccolingually than in the distal half
  40. 40. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 2. Ridges, Fossae, Grooves - Two-cusp version: – Lingual cusp smaller than buccal cusp – Possess more supplemental grooves than first premolars – Also has a smaller triangular ridge
  41. 41. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 2. Ridges, Fossae, Grooves - Two-cusp version: Possess a curved central groove with no lingual groove This groove can be fairly straight D
  42. 42. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 1. Outline - Three-cusp version: – When lingual cusps are large, the occlusal surface is broader on the lingual
  43. 43. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 1. Outline - Three-cusp version: Often have greater bulk buccolingually in the distal not the mesial The ML cusp is usually larger than the DL cusp ML DL
  44. 44. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 2. Ridges, Fossae, Grooves - Three-cusp version: Possess three triangular ridges converging toward the central fossa There is no transverse ridge 1 2 3
  45. 45. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 2. Ridges, Fossae, Grooves - Three-cusp version: Has a central fossa (unique) shifted towards the distal Lacks a central groove Mesial groove present M C D
  46. 46. Occlusal Aspect Of MandibularOcclusal Aspect Of Mandibular Second PremolarSecond Premolar 2. Ridges, Fossae, Grooves - Three-cusp version:  Possess a lingual groove that separates the two lingual cusps  This groove completes the Y-shaped occlusal groove pattern

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