04. Premolars - Dentition

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04. Premolars - Dentition

  1. 1. Cairo University Faculty of Oral and Dental Medicine Prof. Dr. Nahed A. Khalil Head of Oral Biology Department & Contributing Staff Members Human Dentition
  2. 2. PREMOLARS There are four maxillary and four mandibular premolars: Upper 1st premolar: upper 4 Lower 1stpremolar: Lower 4 Upper 2nd premolar: upper 5 Lower 2nd premolar: Lower 5
  3. 3. Maxillary first premolar It has 5 surfaces: Buccal Lingual Mesial occlusal Distal
  4. 4. Geometric outline of the crown Buccal and lingual surfaces have trapezoid outline .The smallest uneven side cervically.
  5. 5. Buccal Outlines Mesial outline is nearly concave. Distal outline is nearly straight. Mesial cusp slope is nearly straight while the distal cusp slope is slightly convex. D Contact areas: Mesially is at the middle third while Distally it is occlusally positioned which is an exception from other permanent posterior teeth. Cervical line: is convex root wise. B cusp pointed and long M
  6. 6. Outline and surface anatomy of the root The M and D outline of the root tapers to a pointed apex that is slightly curved distally. . If it has two roots, the lingual root is hidden behind the buccal root as it’s shorter and narrower than the buccal root. The surface of the root is convex and smooth
  7. 7. Surface anatomy of the crown Elevations: •The buccal surface is convex with the maximum convexity at the cervical 1/3 . •The middle lobe is prominent buccally forming the BUCCAL ridge. Depressions: Shallow depressions are present mesial and distal to the B ridge (M&D developmental grooves)
  8. 8. Lingual outline and surface anatomy of the crown M and D outlines are convex. •The lingual cusp is shorter by 1 mm but sharper than the buccal cusp •The D slope of the lingual cusp is longer than the M slope Cervical line: is convex root wise. The lingual surface is convex with the maximum convexity at the middle 1/3 M D
  9. 9. Outline and surface anatomy of the root The M and D outlines of the root taper to a pointed apex that is curved distally. If two roots, the lingual root appears shorter and narrower than the buccal root. The surface of the root is convex and smooth
  10. 10. Geometric outline of the proximal aspect Distal surface Mesial surface Trapezoid in shape Smallest of the uneven sides is occlusaly
  11. 11. Outlines of proximal aspect Distal surface Mesial surface Buccal outline is convex with the maximum convexity at the cervical 1/3. Lingual outline is convex with maximum convexity at middle1/3. Cervical line curves occlusally and decreased distally.
  12. 12. Distal aspect Mesial aspect Occlusal outline: B cusp is longer than L cusp by 1mm. Wide occlusal table. B cusp tip is below the center of B root. L cusp tip is in one line with the lingual outline of the L root MMRis present at the junction of O 1/3 and M 1/3, while
  13. 13. Proximal surface anatomy Distal aspect Mesial aspect Contact area: At the middle third (OC dimension) and slightly buccal to the midline (BL dimension) Mesial developmental groove is crossing MMR and located lingual to the contact area. Mesial Developmental depression in the crown and continues with that between the roots (canine fossa). Occlusally positioned and more buccally. Smooth and convex surface except for a small flat area cervical to contact area .
  14. 14. Mesial aspect Distal aspect In case of two roots (80%). Root trunk is about half the root length. Surface is smooth and convex except deep developmental depression below bifurcation. Root trunk is longer as the bifurcation is near the apical 1/3 Surface is smooth and convex except shallow DD on the root trunk
  15. 15. In case of one root. The B and L outlines tapers to a blunt apex on the center of the crown. The surface is smooth and convex except for a shallow depression in the center that is deeper mesially than distally.
  16. 16. GEOMETRIC OUTLINE OF THE OCCLUSAL ASPECT It is hexagonal in shape •2 equal buccal sides (MB, DB) D •M side shorter than D side. •ML side shorter than DL side. Thickness is greater than width The crown is wider buccally than lingually. M
  17. 17. Surface anatomy of occlusal aspect: Elevations: B triangular ridge. L triangular ridge. M & D marginal ridges Depressions: Central developmental groove M and D triangular fossae. M marginal developmental groove.
  18. 18. Pulp cavity. MD section BL section Root canals: 2 root canals (B&L) L canal is larger &more accessible Narrow Pulp chamber: Wider
  19. 19. Maxillary second premolar It has 5 surfaces: Buccal Lingual Mesial occlusal Distal
  20. 20. Geometric outline of the crown • Buccal and lingual surfaces have trapezoid outline. The smallest of the uneven sides is cervically.
  21. 21. Facial Outlines and surface anatomy of the crown 4 D M B cusp is long and pointed 5 D M B cusp is short and less pointed M slope is longer than D Mesial contact A is in the M1/3 while distally more occlusal. M slope is shorter than D Mesial contact A is in O1/3 while distally more cervically. Cervical line curved root wise. Cervical line less curved.
  22. 22. 4 D M Prominent B ridge Narrow cervical portion. Short root. 5 D M Less prominent B ridge Wider cervical portion. Longer root.
  23. 23. Lingual outline and surface anatomy of the crown 4 The L cusp is shorter by 1 mm than the B cusp. 80% has 2 roots with L root is shorter than B root and its apex is pointed. 5 The L and B cusps are nearly of same height. Rare to has 2 roots In case of two roots the L root is shorter and its apex is more blunt.
  24. 24. Mesial aspect 4 5 B cusp is longer than L cusp by 1mm The cusps are nearly at the same level. The occlusal table is wide. The occlusal table is narrow. The crown surface is smooth Mesial DG and canine and convex while the root has fossa. shallow developmental depression.
  25. 25. 4 5 MMR at the junction of M1/3 &O1/3 MMR positioned more occlusal. Contact area: At the middle third (OC dimension) and slightly buccal to the midline (BL dimension) At the occlusal third (OC dimension) and slightly buccal to the midline (BL dimension)
  26. 26. Distal aspect 4 5 DMR more occlusal than MMR DMR more cervical than MMR CA occlusally positioned and more buccally than MCA. CA cervically positioned and more buccally than MCA. Smooth and convex surface except for a small flat area cervical to contact area. Smooth and convex surface.
  27. 27. 4 Root trunk is long as the bifurcation is near apical 1/3 Surface is smooth and convex except shallower DD on the root trunk than mesially. 5 One root and if 2 the bifurcation will be more apically. Surface is smooth and convex except deeper DD in the middle of the root than mesially.
  28. 28. Occlusal aspect 5 D M D M It’s oval It’s hexagonal B & L triangular ridges. B & L triangular ridges. M & D marginal ridges Thicker M & D MRs
  29. 29. 4 5 Long Central DG M developmental groove Shorter Central DG. Not present. M and D triangular fossae. M and D triangular fossae.
  30. 30. Mandibular first premolar It has 5 surfaces: Buccal Lingual Mesial occlusal Distal
  31. 31. Geometric outline of the crown • Buccal and lingual surfaces have trapezoid outline. The smallest uneven side is cervically.
  32. 32. Buccal Outlines Mesial and distal outlines are nearly concave Mesial and distal cusp slopes are also slightly concave D Contact areas: Mesially at the junction of O and M thirds while Distally it’s cervically positioned. Cervical line: is convex root wise. B cusp pointed and long M
  33. 33. Outline and surface anatomy of the root The M and D outline of the root tapers to a pointed apex that is curved distally. The surface of the root is convex and smooth
  34. 34. Surface anatomy of the crown Elevations: •The buccal surface is convex with the maximum convexity is at C 1/3 representing cervical ridge. •The middle lobe is prominent buccally forming BUCCAL ridge. Depressions: Shallow depressions are present mesial and distal to the B ridge
  35. 35. Lingual outline and surface anatomy of the crown M and D outlines are convex with marked lingual convergence . The L cusp is short and small reaching 2/3 the crown length and has a pointed tip. Cervical line: is convex root wise. Elevations: The lingual surface is convex with the maximum convixty at M 1/3 Depessions: ML developmental groove at the ML line angle. M D
  36. 36. Geometric outline of the proximal surfaces Distal surface Mesial surface Rhomboid in shape With narrow occlusal table Lingual inclination is well prominent
  37. 37. Outlines of proximal surfaces Distal surface Mesial surface Buccal outline is convex with the maximum convexity at C 1/3 representing ……. Lingual outline is convex with maximum convexity at M1/3 Cervical line curves occlusally and decreased distally
  38. 38. Outlines of proximal surfaces. Distal surface Mesial surface Occlusal outline: the two cusps are not in the same level The B cusp is centered above the root. This is due to the presence of lingual inclination. The L cusp tip is in line with the lingual border of the root.
  39. 39. Outlines of proximal surfaces Distal surface DMR in 4 is straight and at right angle to the axis of the tooth. Mesial surface MMR is inclined from B to L surface to B cusp ridge. DMR is occlusal than MMR (unique characteristic of this tooth).
  40. 40. Proximal surface anatomy Distal surface Mesial surface M & D surfaces are smooth and convex except area cervical to contact area it’s concave. nearly at the same level Contact area it’s broader, cervically and lingually positioned. ML developmental groove is present at the junction of L and M surfaces.
  41. 41. Outline and surface anatomy of the root Distal surface Mesial surface B & L outlines are nearly straight and parallel cervically then taper apically to a blunt apex The surface is more convex The surface is smooth and flat with deep developmental groove
  42. 42. GEOMETRIC OUTLINE OF THE OCCLUSAL ASPECT It’s diamond-shaped. D Lingual convergence is sharp. Mesial outline is slightly curved. Distal outline is more convex. M
  43. 43. Surface anatomy of occlusal aspect: Elevations: B triangular ridge. L triangular ridge. M & D marginal ridges Transverse ridge
  44. 44. Depressions: Central developmental groove M and D triangular fossae. Mesiolingual developmental groove
  45. 45. Mandibular second premolar It has 5 surfaces: Buccal Lingual Mesial occlusal Distal
  46. 46. Geometric outline of the crown • Buccal and lingual surfaces have trapezoid shape with the shortest uneven side cervically.
  47. 47. Buccal outlines and surface anatomy 4 5 B cusp B cusp pointed and long short and less pointed Well developed B ridge Not well developed B ridge Blunt apex Pointed apex
  48. 48. Lingual outline and surface anatomy 4 5 Two cusp type The L cusp is short and small reaching 2/3 the crown length and has a pointed tip. L cusp is shorter and smaller than B cusp but larger than of 4 The lingual surface is convex with maximum convixty at M 1/3 The surface is convex with maximum convixty at O 1/3. No MLDG ML developmental groove at the ML line angle.
  49. 49. Three cusp type: 5 ML cusp is longer and larger than DL cusp.However, both of them are shorter than the B cusp and the ML cusp is less pointed. The surface is convex with the maximum convixty at O 1/3. M The Lingual developmental groove is between the 2 lingual cusps D
  50. 50. Proximal outlines 4 5 Rhomboid in shape with Rhomboid in shape with narrow occlusal table. narrow occlusal table. Lingual inclination well prominentLingual inclination less prominent
  51. 51. 5 4 Maximum convexity at M1/3 The L cusp is short and small reaching 2/3 the crown length Maximum convexity at O1/3 L cusp is shorter and smaller than B cusp but larger than of 4 The B cusp centered over the B cusp tip on line with junction root. of B & M 1/3 of the root. The mesial MR is oplique while distally is straight The mesial and distal marginal ridges are straight
  52. 52. Mesial surface Distal surface Three cusp type: ML cusp is longer and larger than DL cusp. DL cusp is shorter and smaller than ML cusp. Both lingual cusps are shorter than the buccal cusp and the ML cusp is less pointed. Surface anatomy is simillar to that of 4
  53. 53. Geometric outline of the occlusal surface 4 5 It is diamondshaped. It has two cusps. Lingual convergence is sharp. Two cusp type: The outline is oval Slight lingual convergence Three cusp type:The outline is square no lingual convergenc
  54. 54. Surface anatomy of occlusal aspect: 4 5 Elevations: Buccal triangular ridge. Lingual triangular ridge. Transverse ridge M & D marginal ridges
  55. 55. 4 5 Depressions: Central developmental groove M and D triangular fossae. Mesiolingual developmental groove Central developmental groove H or U shapped. M and D triangular fossae.
  56. 56. Lower 5 (Three cusp type): Elevations: Buccal triangular ridge. Lingual triangular ridges (ML &DL). M & D marginal ridges Depressions: Central developmental groove Y shape D triangular M and fossae with M and D pits .

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