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Mandibular Molars

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Mandibular Molars

  1. 1. Mandibular Molars Howard Chi, D.M.D.
  2. 2. Learning Objective • Anatomy of the mandibular molars
  3. 3. Buccal Aspect Of Mandibular Molars • Crown Shape – The crowns of mandibular molars are wider mesiodistally than high cervico-occlusally (greatest extent on first molars)
  4. 4. Buccal Aspect Of Mandibular Molars • First Molar Cusps – The mesiolingual cusp is the highest and widest – The first molar has the largest mesiodistal dimension of any tooth – First molars usually possess three buccal cusps 123
  5. 5. Buccal Aspect Of Mandibular Molars • First Molar Cusps – The mesiobuccal is the largest, widest, and highest cusp on the buccal side – The distobuccal cusp is slightly smaller, shorter, and may be sharper than the mesiobuccal – Distal cusp is on the DB line angle and is the smallest of the five cusps LMS DB Line angle
  6. 6. Buccal Aspect Of Mandibular Molars • First Molar Cusps – The distolingual cusp is the second highest cusp when the tooth is oriented vertically – Even though the lingual cusps are higher than the buccal cusps, clinically the lingual cusp tips are at a lower level than the buccal due to the lingual tilt of the tooth 2nd highest
  7. 7. Buccal Aspect Of Mandibular Molars • Grooves Of The First Molars – The mesiobuccal groove separates the mesiobuccal and distobuccal cusp – There may be a deep pit at the cervical end of this groove – This pit can be a site of caries MB groove Buccal Pit
  8. 8. Buccal Aspect Of Mandibular Molars • Grooves Of The First Molar – The distobuccal groove separates the distobuccal cusp from the distal cusp – It is shorter than the MB groove and not frequently pitted DB groove
  9. 9. Buccal Aspect Of Mandibular Molars • Second Molar Cusps – Four cusps are present on lower second molars – MB cusp is usually wider mesiodistally than the DB cusp – The lingual cusp tips are usually visible from the buccal aspect D M
  10. 10. Buccal Aspect Of Mandibular Molars • Grooves Of The Second Molar – The buccal groove separates the MB cusps from the DB cusp – May end in the middle of the buccal surface in a pit D M Buccal groove
  11. 11. Buccal Aspect Of Mandibular Molars • Proximal Contacts – Same as all molars – Mesial: Junction of the occlusal and middle thirds – Distal: Middle third of crown
  12. 12. Buccal Aspect Of Mandibular Molars • Cervical Line – CEJ is nearly straight across the buccal surface on lower first and second molars – Occasionally a point of enamel will dip down nearly into the root bifurcation – Can also have this type of projection on the lingual, this could lead to periodontal problems Enamel projection
  13. 13. Buccal Aspect Of Mandibular Molars • Taper To The Cervical And The Distal – There is proportionally more tapering of the crown from contact areas to the cervical line on first molars than second molars because of the bulge of the distal cusp #31 #30
  14. 14. Buccal Aspect Of Mandibular Molars • Variations In Mandibular Molar Crowns – The distal cusp is absent one fifth of the time – A four-cusp molar may not always be a second molar - rely on tooth position to aid in determination Absent 1/5 of the time
  15. 15. Roots Of Mandibular Molars • Both mandibular first and second molars have two roots (one mesial and one distal) • Both roots are nearly twice as long as the crown
  16. 16. Roots Of Mandibular Molars • The root bifurcation of a mandibular first molar is near the cervical line • A depression exists between the cervical line and bifurcation • The root trunk relatively short (shorter than lower second molars) Root depression Short root trunk
  17. 17. Roots Of Mandibular Molars • Roots of first molars are widely separated • Second molars have more parallel roots • Roots may possess a distal curve in the apical portion Note distal bend in root
  18. 18. Roots Of Mandibular Molars • From the buccal aspect can see the distal surface of the mesial root because it is twisted on the trunk • The distal root is straighter than the mesial root and may possess a pointed apex • The apex of the mesial root may be in line with the mesiobuccal groove
  19. 19. Lingual Aspect Of Mandibular Molars • Crown Shape From The Lingual – Mandibular first and second molar crowns taper to the lingual – This lingual taper is more evident in first molars – The lingual cusps are longer and more pointed than the buccal cusps #30
  20. 20. Lingual Aspect Of Mandibular Molars • Crown Shape From The Lingual – The mesiolingual cusp is usually longer and wider (slightly) than the distolingual cusp #30 ML DL
  21. 21. Lingual Aspect Of Mandibular Molars • Grooves – The lingual groove separates the mesiolingual cusp from the distolingual cusp – Terminates in the occlusal third with no pit
  22. 22. Lingual Aspect Of Mandibular Molars • Cervical Line – The CEJ is relatively flat mesiodistally – Can dip cervically between the roots over the bifurcation (similar to buccal) – A depression can be seen between the cervical line and the bifurcation
  23. 23. Roots Of Mandibular Molars From The Lingual – On first molars, root trunk appears longer on the lingual than the buccal – This is due to the fact that the cervical line is more occlusal on the lingual surface
  24. 24. Roots Of Mandibular Molars From The Lingual • The roots are narrower on the lingual aspect than the buccal • Can often see the mesial aspect of the mesial root due to the twisting on the trunk • Can see the distal side of the distal root because of taper to the lingual Mesial
  25. 25. Proximal Aspect Of Mandibular Molars • Crown Shape From The Proximal – Appear relatively short occlusocervically compared to faciolingual dimension – The crowns are tilted lingually on the root base – The buccal outline is convex in the cervical third
  26. 26. Proximal Aspect Of Mandibular Molars • Crest Of Curvature – The height of contour on the buccal surface is within the cervical third – On molars this buccal bulge is called the buccal cervical ridge – It is more prominent on second molar than first molars #30
  27. 27. Proximal Aspect Of Mandibular Molars • Cusp Height – The lingual cusps are more conical and pointed than the buccal – They are the largest of the four to five cusps #30
  28. 28. Proximal Aspect Of Mandibular Molars • Distal Tilt – Due to the distal tilt of the crown and the sloping of the occlusal surface, most of the occlusal surface and all cusps can be seen from the distal #30 Distal #31 Distal
  29. 29. Proximal Aspect Of Mandibular Molars • Taper To The Distal – On both first and second molars the crown is more narrow on the distal than the mesial – Can see some of the buccal and lingual surface from the distal due to this taper #30 Distal #31 Distal
  30. 30. Proximal Aspect Of Mandibular Molars • Cervical Line – The mesial CEJ of both first and second molars slopes occlusally from buccal to lingual – The distal cervical line is nearly straight
  31. 31. Proximal Aspect Of Mandibular Molars • Marginal Ridges – The mesial marginal ridge is concave buccolingually – Usually longer on first molars than second and V-shaped on the second
  32. 32. Occlusal Aspect Of Mandibular Molars • Lingual Inclination – Due to lingual inclination a considerable portion of the buccal aspect can be seen from this view – The molars are wider mesiodistally than faciolingually
  33. 33. Occlusal Aspect Of Mandibular Molars • Shape: Rectangular Or Pentagon – The second molar is roughly rectangular – The first molar with the distal cusp is more like a pentagon – The two mesial cusps are larger than the two distal cusps D M M D
  34. 34. Occlusal Aspect Of Mandibular Molars • Taper To The Distal And Lingual – The crown is narrower buccolingually on the distal than the mesial – The crown is narrower mesiodistally on the lingual than the facial D M M D
  35. 35. Occlusal Aspect Of Mandibular Molars • Taper To The Distal And Lingual – The widest portion of the crown of a second molar buccolingually is opposite the mesial cusps – The widest portion of the crown of a first molar buccolingually is opposite the distobuccal cusp D M M D
  36. 36. Occlusal Aspect Of Mandibular Molars • Ridges – On both first and second molars the MB and ML cusp’s triangular ridges form a transverse ridge – The same is true for the DB and DL cusps – Since lingual cusps are taller, they possess longer triangular ridges than the buccal
  37. 37. Occlusal Aspect Of Mandibular Molars • Fossae – Mandibular molars possess three fossae, a large central fossa, a smaller mesial, and the smallest distal fossa – Each or all may possess a pit
  38. 38. Occlusal Aspect Of Mandibular Molars • Grooves: First Molar – The central groove is more zigzag or crooked in its mesiodistal course – There are two buccal grooves instead of one found on lower second molars MB Groove DB Groove
  39. 39. Occlusal Aspect Of Mandibular Molars • Grooves: Second Molar – Groove is simpler than first and resembles a cross – Central groove is straighter than that of the first molar – Buccal and lingual grooves are usually continuous
  40. 40. Mandibular Third Molars • Shape And Relative Size – Shortest of mandibular teeth – Crown may resemble a first or second molar – Generally have bulbous crowns #32 Buccal #32 Distal
  41. 41. Mandibular Third Molars • Distal Tip – The crown tips distally and the distal half of the crown is noticeably shorter
  42. 42. Mandibular Third Molars • Cusp Size – Lingual cusps are the longest and largest, with ML being biggest • Grooves – Irregular groove pattern with multiple supplemental grooves
  43. 43. Mandibular Third Molars • Roots – The two roots tend to be short and are often fused – If the roots are separate the root trunk will be long – Can possess one or more extra roots #32 Lingual #32 Mesial

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