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Mandibular Premolars

Mandibular Premolars. Introduction. Mandibular 1st smaller than 2nd F-L and M-D dimensions nearly equal (F-L slightly greater) L cusps are much smaller than F Crowns tilted lingually Less similarity between 1st and 2nd. Mandibular First Premolar. General Characteristics:.

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Mandibular Premolars

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  1. Mandibular Premolars

  2. Introduction • Mandibular 1st smaller than 2nd • F-L and M-D dimensions nearly equal (F-L slightly greater) • L cusps are much smaller than F • Crowns tilted lingually • Less similarity between 1st and 2nd

  3. Mandibular First Premolar

  4. General Characteristics: • Arch position: 4th from midline • Universal #21 and #28 • Only facial cusp functional • Closer in form & function to canine

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

  6. Facial View • Pentagonal (5-sided) • Geometric: trapezoid • Both mesial and distal HOC at middle third* • Facial HOC at cervical third • Cusp tip offset towards mesial • MB cusp ridge shorter • DB cusp ridge longer

  7. Lingual View • Diminished lingual cusp (most variable in size) • Most of buccal cusp visible • L surface much narrower than F • Presence of ML groove*(unique) • Lingual HOC at middle third

  8. Mesial View • Rhomboidal geometric form • Crown inclined lingually • Buccal cusp tip centered over root midline* • Lingual cusp tip centered over lingual root surface

  9. Mesial view… • Mesial marginal ridge incline of 45o* • Mesial marginal ridge more cervical than distal* • ML groove present*

  10. Distal View • Distal marginal groove (?) • No DL developmental groove • Distal marginal ridge more horizontal*

  11. Occlusal View • Outline is diamond-shaped • Buccal cusp occupies 2/3 of occlusal surface* • B and L cusp tips offset mesially • Occlusal table is triangular

  12. Occlusal view… • Mesial outline indented by ML groove - looks like “closed fist” • Pronounced transverse ridge* • M and D pits may be connected by central groove • Distal fossa larger, circular • Mesial fossa more linear

  13. Root Form • Usually single rooted, bifurcation possible (but rarely) • Wider F-L than M-D • Cross-section is ovoid, wider buccally than lingually

  14. Variations and anomalies: • Absence of ML groove • Lingual cusp size variable • Central groove not evident

  15. How To Tell Right From Left: • Presence of ML groove • Mesial marginal ridge slopes more than distal marginal ridge • MB cusp ridge shorter than DB cusp ridge • Distal fossa circular, mesial is linear • Cusps offset towards mesial

  16. Mandibular Second Premolar

  17. General characteristics: • Arch position: 5th from midline • Universal #20 and #29 • Proximal geometric form: rhomboidal • Generally larger crown, larger and longer root

  18. General characteristics… • May have two or three cusps • One facial • One or two lingual • Occlusal table resembles small molar

  19. Development Timeline: • Initial calcification: 2 1/4 - 2 1/2 years • Enamel completed: 6 - 7 years • Eruption: 11 - 12 years • Root completed: 13 - 14 years

  20. Facial View • Resembles 1st from this view except: • Cusp tip not as sharp • MB and DB cusp ridges not as steeply inclined • Cusp tip centered mesiodistally*

  21. Lingual View • Lingual cusps generally better developed than 1st • Lingual HOC at occlusal third* (unique) • Three cusp variety: • ML cusp larger than DL • Lingual groove present

  22. Mesial View • Lingual inclination less than 1st • Buccal cusp tip is facial to tooth midline* • Mesial marginal ridge nearly horizontal • Mesial marginal groove present, no ML developmental groove • Only two cusps visible

  23. Distal View • Distal marginal ridge more cervical than mesial • More of occlusal surface visible from this view • All 3 cusp tips visible from this view (3-cusp variety)

  24. Occlusal View • General outline more square • Less taper lingually than 1st* • Three occlusal groove patterns: • Y-type (3 cusp variety) • U-type (2 cusp) • H-type (2 cusp)

  25. Three cusp variety: • Y shape groove pattern • Formed by lingual groove joining central groove • Only premolar with lingual groove* • Largest to smallest cusps: • B, ML, DL

  26. Three cusp variety... • No transverse ridge (?) • 3 pits: mesial, central, distal • 3 fossae: • 2 triangular fossae: mesial and distal • 1 central fossa

  27. Two cusp variety: • U or H shape groove patterns • More rounded than 3-cusp variety • Transverse ridge present • No lingual groove or central pit

  28. Two cusp variety... • Lingual cusp offset to mesial • 2 pits: mesial and distal • 2 triangular fossae: mesial and distal

  29. Root Form • Normally single, bifurcation possible • Root cross-section is ovoid

  30. Anomalies: • May be missing congenitally

  31. How To Tell Right From Left: • ML cusp larger than DL (3-cusp) • Lingual cusp offset mesially (2-cusp) • Distal marginal ridge more cervical than mesial marginal ridge • Root may have distal deflection

  32. How To Tell 1st from 2nd: • Greater disparity between F and L cusp heights with 1st • ML groove present in 1st • Mesial marginal ridge slopes more in 1st (45o) • 2nd typically 3-cusp variety

  33. 1st from 2nd… • Occlusal outline more rounded in 1st, more square in 2nd • Buccal cusp tip centered over root apex in 1st, facial of center in 2nd*

  34. Tooth ID

  35. General characteristics of mandibular premolars: • First and second have more dissimilarities than maxillary • First is smaller than second

  36. Mandibular premolars... • 4 - 5 developmental lobes • F-L and M-D crown dimensions more equal • Buccal cusps larger than linguals • Crowns have lingual inclination • Lingual HOC more occlusal

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