Maxillary First Premolar

7/28/2019 Maxillary First Premolar

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Maxillary First Premolar

Function: tearing

Chronology:Beginning of calcification 1.5-1.75 yrsCrown completed 5-6 yrsEruption 10-11 yrsRoot completed 12-13 yrs

Number of lobes: 4 lobes (3 buccal and 1 lingual)

Buccal Aspect

Geometric outline:

Trapezoid (cusp tip is not included) Smallest uneven side cervically

Larger side occlusally

Outlines of crown and root:Crown Outline

Mesial and distal outlines are nearly concave

Mesial and distal cusp slopes are slightly concave

Cervical: convex root wise

Buccal Cusp tip is pointed and long representing the

overdevelopment of the middle lobe Contact area Mesially is middle 1/3 while Distally is

occlusally positioned (different to other posterior teeth as themesial slope is longer than distal slope)

Root outlineMesial and Distal outline of the roots tapered to a pointed apex thatcurved distallyIf there are two roots, the buccal root hides the lingual root as itsshorter and narrower than the buccal root

Surface anatomy of the crown and rootElevations

Crown Surface is convex and smooth with max convexity atcervical 1/3 representing cervical ridge ( linear elevation found onthe cervical 1/3 of the buccal surface of crown of all teeth)

The middle lobe is prominent buccally forming buccal ridgelinear elevation found on the middle lobe of the buccal aspectdue to the over development of the middle lobe

Root is smooth and convexDepressions

Shallow depressions present mesial and distal to the buccalridge. These depressions are linear depressions found on the


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buccal aspect of premolars, representing the completeunion/fusion of the lobes.

Lingual Aspect

Geometric outline of the crown

Similar to buccal

Outlines of the crown and rootCrown Outline

Mesial and Distal outlines are convex

Distal slope of L cusp is longer than mesial slope

Cervical line is convex root wiseRoot Outline

If two root, lingual root will appear shorter and narrower thanthe buccal root

Mesial and Distal outline of the roots tapered to a pointedapex that curved distally

Surface anatomy of the crown and root

Crown Surface is convex with maximum convexity at themiddle 1/3

Root surface is convex and smooth


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Mesial Aspect


Trapezoid

Smallest uneven side occlusally

Longer side cervically

Outlines of the crown and rootCrown OutlineBuccal outline is convex with maximum convexity at cervial 1/3representing cervical ridgeLingual outline is convex with maximum convexity at middle 1/3Lingual outline is more convex than buccal outlineOcclusal outline is formed by two cusps(Lingual and Buccal)

Buccal cusp is longer than L cusp by 1mm

Wide occlusal table

B cusp tip is below the centre of B root

L cusp tip is online with L root

MMR present at the junction of O and M 1/3

Cervical line curves occlusally and decreased distally

Root OutlineTwo roots

In case of 1 root B and L outline tapered to a blunt apex on thecentre of the crown

Surface anatomy of the crown and root

Elevations


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Contact area is located in the middle 1/3 and slightly buccal tomidline (BL dimension)

Mesial Marginal DG crosses MMR and located lingual to thecontact area. Developmental groove ends on the mesial side

Root surface is smooth and convex except for the deepdevelopmental depression below bifurcation. Root trunk is about the root length

Depressions

Mesial Developmental depression found in the crown andcontinue with that on the root (canine fossa)

In case of one root the surface will have a shallow depression inthe centre that is deeper mesially than distally due to canine fossa

Distal Aspect


Similar to mesial

Outlines of the crown and root

Similar to mesial


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Occlusal Aspect


Hexagonal (thickness > width)

Outlines of the crown and root

Crown Outline 2 equal buccal sides(MB and DB)

M side shorter than D side

ML side shorter than DL side (lingual side is rounded)

Surface anatomy of the crown and rootElevations

Buccal Triangular Ridge (linear elevations found on the buccalcusps on occlusal surfaces of posterior teeth)

Lingual Triangular Ridge (linear elevations found on the Lingual

cusps on occlusal surfaces of posterior teeth) Mesial and Distal Marginal Ridges (linear elevation found on the

mesial and distal margins on the occlusal surfaces of posteriorteeth)

Depressions

Central developmental groove (Linear depressionsrepresenting the complete union/fusion of lobes, found on theocclusal surfaces of posterior teeth)

Mesial and Distal Triangular Fossae (small depression or

concavity found on the occlusal surfaces of posterior teeth

mesial and distal to the marginal ridges)


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Mesial Marginal developmental groove (linear depressionfound on the mesial side of upper first premolars due to thecentral developmental groove crossing the mesial marginalridge)

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Maxillary First Premolar