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Prof. A. El- sahn

(9). THE PREMOLARS. Prof. A. El- sahn. GENERAL CHARACTERISTICS. The premolars are so named because they are situated in front of the permanent molars. They replace the deciduous molars, so they are succedaneum teeth (no premolars in the deciduous dentition). Prof. A. El- Sahn. B. B.

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Prof. A. El- sahn

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  1. (9) THE PREMOLARS Prof. A. El-sahn

  2. GENERAL CHARACTERISTICS • The premolars are so named because they are situated in front of the permanent molars. • They replace the deciduous molars, so they are succedaneum teeth (no premolars in the deciduous dentition). Prof. A. El- Sahn

  3. B B B B L L L L • They have usually two cusps, buccal and lingual, so they are called bicuspid. B • This term, which is widely used, is misleading, since mandibular premolars may show a variation in the number of cusps from one to three. L Prof. A. El- Sahn

  4. They are developed from four lobes as anterior teeth, three buccal and one lingual except the lower second premolar, which may develop from five lobes. • The lingual cusp developed from the lingual lobe, which is represented by the cingulum in anterior teeth. • The middle buccal lobe of the premolars is highly developed. It corresponds to the middle labial lobe of the canine. Prof. A. El- Sahn

  5. The premolars differ from the anterior teeth in the following: • The premolars are wider bucco-lingually than mesio-distally. b) They have occlusal surfaces with well-developed cusps instead of incisal edges. B D M D M L B L Prof. A. El- Sahn

  6. c) Their marginal ridges are part of the occlusal surface and are oriented nearly in a horizontal plane instead of vertically as in anterior teeth. d) Their crown and roots are shorter than those of the maxillary canines. Prof. A. El- Sahn

  7. e) The contact areas of premolars (and molars) are nearly at the same level, broad and are more cervically than those for anterior teeth. Prof. A. El- Sahn

  8. f)Proximally, the crests of curvatures of both buccal and lingual surfaces of the crown are more occlusal than the corresponding crests of curvature in anterior teeth. g) Their cervical line is less curved proximally. B L • L B Prof. A. El- Sahn

  9. FUNCTION OF PREMOLARS • The premolars assist the canines in tearing of food by the sharp cusp tips of first premolars and assist the molars in mastication of food. • The premolars function with molars in maintaining the vertical dimension of the face. • They support the corners of the mouthand cheeks to keep them from sagging. PM Prof. A. El- Sahn

  10. second first MAXILLARY PREMOLARS Prof. A. El- Sahn

  11. There are four maxillary (upper) premolars: two in each side of the maxillae; the first and the second. • The first and second upper premolars are posterior to the upper canines. 14 24 15 • 25 Prof. A. El- Sahn

  12. second first maxillary • The maxillary first and second premolars are more alike than the mandibular premolars. first second mandibular Prof. A. El- Sahn

  13. The maxillary first premolar is larger than the second premolar, unlike the mandibular premolars. Prof. A. El- Sahn

  14. The maxillary first premolar has a longer crown and a shorter rootthan the second premolar. first first Prof. A. El- Sahn

  15. MAX. first • The cusps of maxillary and mandibular first premolars are moresharp than the second premolars. Mand. first Prof. A. El- Sahn

  16. MAXILLARY FIRST PREMOLAR Prof. A. El- Sahn

  17. 1 2 3 4 • The maxillary first premolar is the fourth tooth from the midline. • Its mesial side is in contact with the distal side of the adjacent canine. Prof. A. El- Sahn

  18. It has a mesial depression extending from the root area to the cervical half of the crown, which is called the "canine fossa". M D M Prof. A. El- Sahn

  19. B • Its crown is angular with prominent buccal line angles. D M L Prof. A. El- Sahn

  20. Maxillary first premolar has two well-formed roots in about 60%-61% of the cases, a buccal and a lingual root. Prof. A. El- Sahn

  21. CHRONOLOGY Prof. A. El- Sahn

  22. BUCCAL ASPECT The Crown Its geometric outline is roughly trapezoidal with the smallest of the uneven sides is cervically. Prof. A. El- Sahn

  23. BUCCAL ASPECT D M Prof. A. El- Sahn

  24. Prof. A. El- Sahn

  25. Contact Areas Prof. A. El- Sahn

  26. Occlusal Outline • The tip of the buccal cusp is slightly distal to the vertical axis of the tooth because its mesial slope is longer than the distal slope. D Prof. A. El- Sahn

  27. M D • The mesial slope is nearly straight or slightly concave, and is sometimes notched, while the distal slope is convex. • This is the only tooth, considering canine and other premolars, on which mesial cusp slope is longer than the distal slope. Prof. A. El- Sahn

  28. The buccal cusp is relatively long, and pointed, and resembles that of maxillary canine. Prof. A. El- Sahn

  29. Cervical Line • It shows little curvature towards the root. Prof. A. El- Sahn

  30. Morphology of the buccal surface • The buccal surface is convex. • There is prominent elevation in the middle of the crown running from the cusp tip to the cervical margin, it is called the buccal ridge. • This ridge is due to strong development of the middle lobe. Prof. A. El- Sahn

  31. Two shallow vertical developmental depressions mesialand distal to the buccal ridge (B.R.). • The one on the mesial side is deeper. • The mesio-buccaland disto-buccal line angles are prominent. • The cervical ridge ( C.R.) occupies the cervical third of the buccal surface.. C. R. B. R. D.D M.D. D M Prof. A. El- Sahn

  32. The Root D M D M M D • It is conical in form with pointed apex. • Its apical third may curve distally and sometimes curve mesially. • Its buccal surface is convex. Prof. A. El- Sahn

  33. The Lingual Aspect The Crown • The crown is a little narrower lingually than buccally because of the lingual convergence of the proximal sides. • The mesial and distal outlines of the lingual portion of the crown are convex. Prof. A. El- Sahn

  34. Occlusal Outline • The lingual cusp is shorter than the buccal cusp by about 1 mm. • The mesialand distal slopes of the lingual cusp meet at the cusp tip at a somewhat rounded angle but is still a sharp cusp compared to the molars. -1 mm. Prof. A. El- Sahn

  35. M D • The slopes of the lingual cusp are continuous with the convex proximal outlines of the crown lingually. • The mesial slope is shorter than the distal and the cusp tip is mesial to the buccal cusp tip. • The lingual surface is convex in all directions. Prof. A. El- Sahn

  36. Cervical Line • It shows slight curvature towards the root. Prof. A. El- Sahn

  37. B L 0.8 mm. The Root • The lingual portion of the root(if the tooth is single rooted) or the lingual surface of the lingual root (if two roots are present) is convex and narrowermesio-distally than the buccal portion. • The lingual root (if two roots are present) is shorter than the buccal root by about 0.8 mm. Prof. A. El- Sahn

  38. The Root ( cont.) • The apex of the lingual root tends to be more blunt than the buccal root apex. • The apical end of the lingual rootmay bend mesially or distally. Prof. A. El- Sahn

  39. Cont. will be … next Wednesday !!!.

  40. The Mesial Aspect • Geometrically, the crown is roughly trapezoidal with the small uneven side occlusally. The Crown Prof. A. El- Sahn

  41. The buccal and lingual cusps are long and sharp. L B • The buccal cusp is longer than the lingual cusp by about 1 mm. • The buccal cusptip is directly below the center of the buccal root (in two- rooted tooth) ,and is nearer the center of the root trunk than is the lingual cusp. +1 mm. Prof. A. El- Sahn

  42. Buccal Outline L B • Is convex from the cervical line to the tip of the buccal cusp. • The crest of curvature is usually at the junction of the middle and cervical third (or it may be located within the cervical third) making the cervical ridge. Prof. A. El- Sahn

  43. Lingual Outline L • Is smoothly convex line from the cervical line to the tip of the lingual cusp. • The crest of curvature is usually at the center of the middle third. Prof. A. El- Sahn

  44. The tip of the lingual cusp may be on a line with the lingual border of the lingual root. • As in all posterior teeth, the distance between the tips of the buccal and lingual cusps is less than the bucco-lingualmeasurement at the cervix. L B Prof. A. El- Sahn

  45. Both cusp tips are located well within the boundary of the root contour. • This is an important relationship for good support for large chewing area. Prof. A. El- Sahn

  46. The mesial marginal ridge is horizontallyconcave from buccal to lingualand forms the occlusal border of the mesial surface. • The mesial marginal ridge is at about the level of the junction of the middle and occlusal thirds. Distal aspect • It is more occlusally positioned than the distal marginal ridge. Prof. A. El- Sahn

  47. This marginal ridge developmental groove crosses the marginal ridge immediately lingual to the mesial contact area and extends for a short distance on the mesial surface. • The mesial marginal ridge is usuallycrossed by a developmental groove. B L Prof. A. El- Sahn

  48. This groove is continuous with the central groove of the occlusal surface. The marginal ridge grooveserves as a spillway for food during mastication Prof. A. El- Sahn

  49. Cervical Line • It slightly curvesocclusally in a curvature averaging about 1 mm. Prof. A. El- Sahn

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