Prof. A. El-sahn

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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

GENERAL CHARACTERISTICS

They have usually two cusps, buccal and lingual, so they are called bicuspid.

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This term, which is widely used, is misleading, since mandibular premolars may show a variation in the number of cusps from one to three.

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Prof. A. El- Sahn

The lingual cusp developed from the lingual lobe, which is represented by the cingulum in anterior teeth.

Prof. A. El- Sahn

The middle buccal lobe of the premolars is highly developed.

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.

It corresponds to the middle labial lobe of the canine.

The premolars differ from the anterior teeth in the following:a) The premolars are wider

bucco-lingually than mesio-distally.

b) They have occlusal surfaces with well-developed cusps instead of incisal edges. Prof. A. El- Sahn

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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

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

g) Their cervical line is less curved proximally.

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.

Prof. A. El- Sahn

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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 mouth and cheeks to keep them from sagging.

Prof. A. El- Sahn

FUNCTION OF PREMOLARS

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MAXILLARY PREMOLAR

SProf. A. El- Sahn

first second

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. Prof. A. El- Sahn

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The maxillary first and second premolars are more alike than the mandibular premolars.

Prof. A. El- Sahn

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

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

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The cusps of maxillary and mandibular first premolars are more sharp than the second premolars.

Prof. A. El- Sahn

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MAXILLARY FIRST

PREMOLAR

Prof. A. El- Sahn

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

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It has a mesial depression extending from the root area to the cervical half of the crown, which is called the "canine fossa".

Prof. A. El- Sahn

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Prof. A. El- Sahn

Its crown is angular with prominent buccal line angles.

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Prof. A. El- Sahn

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

Initial Calcification18 – 21

months after birth

Completion of Crown

5 – 6 years

Eruption 10 – 11 years

Completion of Root 12 – 13 years

CHRONOLOGY

Prof. A. El- Sahn

BUCCAL ASPECT

The CrownIts geometric outline is roughly trapezoidal with the smallest of the uneven sides is cervically. Prof. A. El- Sahn

Mesial outline

is slightly concave from the cervical line to the mesial contact area.

Distal outline

is nearly straight from the cervical line to the distal contact areas.

BUCCAL ASPECT

Prof. A. El- Sahn

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Prof. A. El- Sahn

The junction of mesial and distal surfaces and cusp slopes is more broad, bulging and angular, and more than the second premolars.

Mesial:

Is relatively broad. It is usually in the middle third just cervical to the junction of the occlusal and middle thirds.

Prof. A. El- Sahn

Contact Areas

Distal: Is broader than the mesial contact area. It is in the middle third, slightly more cervically than the mesial contact area. The two contact areas are nearly at the same level more than those found on anterior teeth.

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. Prof. A. El- Sahn

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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

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

Cervical Line

It shows little curvature towards the root. Prof. A. El- Sahn

This ridge is due to strong development of the middle lobe.

Morphology of the buccal surface

The buccal surface is convex.

Prof. A. El- Sahn

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.

The one on the mesial side is deeper.

Two shallow vertical developmental depressions mesial and distal to the buccal ridge (B.R.).

Prof. A. El- Sahn

The mesio-buccal and disto-buccal line angles are prominent. The cervical ridge ( C.R.) occupies the cervical third of the buccal surface..

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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

DDD MMMThe Root

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.

The Lingual Aspect

Prof. A. El- Sahn

The Crown

Occlusal Outline

The lingual cusp is shorter than the buccal cusp by about 1 mm.

The mesial and 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.Prof. A. El- Sahn

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The slopes of the lingual cusp are continuous with the convex proximal outlines of the crown lingually.

Prof. A. El- Sahn

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The lingual surface is convex in all directions.

The mesial slope is shorter than the distal and the cusp tip is mesial to the buccal cusp tip.

Cervical Line

It shows slight curvature towards the root.

Prof. A. El- Sahn

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 narrower mesio-distally than the buccal portion.

The Root

The lingual root (if two roots are present) is shorter than the buccal root by about 0.8 mm.

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The apex of the lingual root tends to be more blunt than the buccal root apex.

The apical end of the lingual root may bend mesially or distally.

The Root ( cont.)

Prof. A. El- Sahn

Cont. will be … next Wednesday !!!.

Geometrically, the crown is roughly trapezoidal with the small uneven side occlusally.

The Mesial Aspect

Prof. A. El- Sahn

The Crown

The buccal cusp tip 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.

Prof. A. El- Sahn

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The buccal and lingual cusps are long and sharp.

The buccal cusp is longer than the lingual cusp by about 1 mm.

Buccal Outline

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

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Lingual Outline

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

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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-lingual measurement at the cervix.

Prof. A. El- Sahn

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Both cusp tips are located well within the boundary of the root contour.

Prof. A. El- Sahn

This is an important relationship for good support for large chewing area.

It is more occlusally positioned than the distal marginal ridge.

The mesial marginal ridge is horizontally concave from buccal to lingual and forms the occlusal border of the mesial surface.

Prof. A. El- Sahn

The mesial marginal ridge is at about the level of the junction of the middle and occlusal thirds.

Distal aspect

The mesial marginal ridge is usually crossed by a developmental groove.

Prof. A. El- Sahn

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.

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Prof. A. El- Sahn

This groove is continuous with the central groove of the occlusal surface.

The marginal ridge groove serves as a spillway for food during mastication

Cervical Line

It slightly curves occlusally in a curvature averaging about 1 mm.

Prof. A. El- Sahn

Morphology Of The Mesial Surface On the mesial surface of

the crown a mesial developmental depression is found.

This depression is cervical to the mesial contact area and is centered on the mesial surface between the two mesial line angles.

Prof. A. El- Sahn

This depression is continuous with the developmental depression on the mesial surface of the root (or root trunk) forming what is sometimes called "canine fossa".

Prof. A. El- Sahn

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This depression is a distinguishing feature of the maxillary first premolar, which is not found on any other premolar.

The Mesial Contact Area

It is relatively broad.

It lies in the middle third just cervical to the junction of the occlusal and middle thirds.

Bucco-lingually, it lies buccal to the junction of the buccal and middle thirds. Prof. A. El- Sahn

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Most maxillary first premolars have two roots (about 61%), one buccal and one lingual which are distinguishing characteristic of this tooth.

The Root

Prof. A. El- Sahn

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In the two-rooted type

The root trunk is long in this tooth, making up about half of the tooth length.

The bifurcation mesially begins at a more occlusal point than distally.

Prof. A. El- Sahn

The mesial surface of the roots is smoothly convex.

Prof. A. El- Sahn

The root trunk shows a deep developmental depression on its mesial surface, at or below the bifurcation, which is continuous with the mesial depression on the crown.

In single-rooted teeth

(about 38%), the relatively straight buccal and lingual outlines of the root end in a blunt apex above the center of the crown.

The mesial surface of the root portion is convex buccally and lingually with prominent developmental depression for most of the root length. Prof. A. El- Sahn

Distal Aspect

The distal aspect of this tooth is similar to its mesial aspect, with the following differences:

Prof. A. El- Sahn

The Crown The distal surface is

convex except for a small flat area just cervical to the contact area and buccal to the center of the distal surface.

There is no deep developmental groove crossing the distal marginal ridge. If a groove is found, it is shallow and insignificant.

Prof. A. El- Sahn

The distal contact area is slightly buccal to the mesial contact area. The distal contact area is broader than the mesial one.

The cervical line is less curved on the distal than on the mesial surface.

The distal marginal ridge is slightly more cervically than the mesial one.

The bifurcation of the roots is near the apical third, so the root trunk is longer distally and the divided part of the root is shorter (about the apical third) than mesially. Prof. A. El- Sahn

The Root

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On the middle third of the root trunk or root (on both double - and single - rooted teeth) there is a depression less deep than those on the mesial side.

Prof. A. El- Sahn

The distal surface of the root near the cervix is usually convex or flat.

Occlusal Aspect

The geometric outline of the occlusal surface is roughly hexagonal (six-sided).

The six sides are made up of two buccal, two lingual and two proximal sides.

Prof. A. El- Sahn

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than the distal side and

the mesio-lingual side is shorter than the disto-lingual side.

The two buccal sides (mesio-buccal and disto-buccal) are nearly equal, the mesial side is shorter

Prof. A. El- Sahn

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The bucco-lingual dimension of the crown is much greater than the mesio-distal

The rounded hexagonal shape is not equilateral.

The crown is wider on the buccal than

on the lingual due to lingual convergence of the proximal sides.

dimension.

Both the buccal and lingual cusps have mesial and distal cusp ridges (or slopes) which meet at the cusp tip and merge with the marginal ridges.

Prof. A. El- Sahn

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The lingual cusp ridges are curved, forming a semi-circular outline, and the crest of curvature is at the tip of the lingual cusp, which is mesially placed in relation to the buccal cusp.

The two cusps are sharper than those of the maxillary second premolar and the buccal cusp is larger than the lingual.

Prof. A. El- Sahn

Buccal and lingual triangular ridges extend from the buccal and lingual cusp tips respectively to the central developmental groove.

maxillary second

The buccal triangular ridge is more prominent than the lingual triangular ridge.

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The mesial marginal ridge is shorter bucco-lingually than the more convex distal marginal ridge, and is usually crossed by the mesial marginal ridge groove.

Prof. A. El- Sahn

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Marginal ridges:

Central developmental groove: The central developmental

groove runs across the central part of the occlusal surface.

This groove is longer than that of the maxillary second PM.

The central groove ends mesially and distally in-pits in the mesial and distal triangular fossa, where it meets the supplemental grooves of the fossae.

Prof. A. El- Sahn

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The mesial marginal groove connects the central developmental groove in the mesial triangular fossa and is considered a mesial extension of that groove.

Triangular Fossae There are two

triangular depressions or fossae just distal and mesial to the mesial and distal marginal ridges, which form their bases.

Prof. A. El- Sahn

DM

The Mesial Triangular Fossa :

Is slightly smaller and less deep than the distal one.

In this fossa (M), the mesial end of the central groove meets two collateral supplemental grooves, which are called the mesio-buccal and mesio-lingual supplemental grooves.

The point of union is called the mesial developmental pit.

Prof. A. El- Sahn

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The Distal Triangular Fossa:

Is just mesial to the distal marginal ridge.

In this fossa the central developmental groove meets its two collateral supplemental grooves at the distal developmental pit.

Prof. A. El- Sahn

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The disto-lingual supplemental groove of the distal triangular fossa is very short.

The distal marginal ridge may be crossed by a marginal groove similar to that of the mesial marginal ridge.

Contact areas from the occlusal aspect

Mesial contact area is buccal to the junction of the buccal and middle thirds. Distal contact area is slightly buccal to the mesial contact area (the opposite of second premolars). Prof. A. El- Sahn

Variations The buccal root may be

divided into a mesio and disto-buccal root giving a total of three roots (and three root canals).

There may be just a single longitudinally grooved root.

Prof. A. El- Sahn

Maxillary 1st PremolarsPertinent DataUniversal CodeUniversal Code

International CodeInternational Code

Palmer NotationPalmer Notation

Number of RootsNumber of Roots

5

14

4

12

24

4

1 (40%) 2 (60%)

Right

Left

Number of Root CanalsNumber of Root Canals 2

Number of pulp HornsNumber of pulp Horns

Number of Developmental Lobes

Number of Developmental Lobes

2

4

Number of Cusps 2

Maxillary First PremolarsPertinent Data

MesialMesial Middle thirdMiddle third

DistalDistal

Location of proximal contact areas:

FacialFacial Jun. of Middle & Cervical third

Jun. of Middle & Cervical third

LingualLingual

Center of Middle thirdCenter of Middle third

Height of contour:

Middle thirdMiddle third