upper premolars (2)

THE PREMOLARS

General features

- The term "bicuspid" is often used for of premolar, but this is inaccurate since the mandibular second premolar may show three cusps.

- There are eight premolars-two in each quadrant .They are successors for the deciduous molars.

- The premolars are neighbored mesially by the canines and distally by the molars. They erupts following the shedding of their predecessors(deciduous molars).

- The premolars are developed from four lobes, three buccal lobes ( the three form the buccal cusp) and one lingual ( for the single lingual cusp), except the mandibular second premolar (the three cusp form) in which it develops from five lobes, three buccal and two lingual( as it has two lingual cusp).

- Usually the first premolars assist the canines in their function of tearing.While the second premolars assist the molars in their grinding function.

- Premolars resembles canine yet the main differences are:

Ass. Prof. /Reham Magdy1

It resembles the canine from the buccal aspect, but differs in that:

Premolars Canine

Less curvature of the cervical line mesially and distally.

Cervical line is more curved mesially and distally

The contact areas are about the same level.

Contact areas with different levels

They have occlusal surface . They have incisal ridges

Greater relative buccolingual measurement as compared with the mesiodistal measurement than that of the canine. Premolars has shorter crown cervico-occlusal .

Marginal ridge is found mesial and distal to the occclusal surface.

Marginal ridge is found mesial and distal to the lingual surface

The mesial slope of the buccal cusp of the first premolars is longer than the distal slope

The distal slope of the canines is longer than the mesial slope

The root is shorter The roots are longer


THE MAXILLARY FIRST PREMOLAR

* This tooth is the usually has two roots (about 80%) a buccal and a lingual with two pulp canals. While in (20%) of the cases it has single root.

- The maxillary first premolar has two well developed cusps , buccal and lingual. The buccal cusp is longer than the lingual cusp by about 1 m.m.

Chronology:

Appearance of dental organ 7 m.I.U.

First evidence of calcification 1 - 1 year

Enamel completed 5-6 years

Eruption 10-11 years

Root completed 12-13 years

Buccal aspect

*Geometrical outline : The crown is roughly trapezoid with the smallest uneven sides directed cervically.

*Outline:

The mesial outline of the crown is slightly concave from the cervical line to the mesial contact area which is present slightly cervical to the occlusal third ( about junction level) . Also mesial cusp slope is concave and longer than distal one.


The distal outline is less concave till the contact area. The contact distally is broader than the mesial, and tends to be more occlusal.The distal slope is slightly convex.

The buccal cusp is long and located distal to the midline ( as the mesial slop is longer)

*The cervical line :The cervical line is curved rootwise.

*Surface anatomy:

The buccal surface has a cervical ridge present in the cervical third of the buccal surface. The crown surface is convex, with a continuous ridge from the cusp tip to the cervical margin which is called the buccal ridge. This ridge denotes strong development of the middle buccal lobe.

Two developmental grooves, the mesiobuccal and distobuccal, are located on both sides of the buccal ridge and mark the union of the developmental lobes.

*Roots: The buccal root outline resembles that of the maxillary canine but is shorter .

Lingual aspect

-The crown converges lingually . The lingual cusp is shorter and narrower mesiodistally than the buccal cusp. Since the lingual cusp is shorter than the buccal cusp, the tips of both cusps with their mesial and distal slopes may be seen from this aspect.

-The mesial and distal outlines , as well as mesial and distal slopes of the lingual cusp are convex.

-The tip of the lingual cusp is pointed and located slightly mesial.


-The mesial slope of the lingual cusp is shorter than the distal slope.

-The crown is smooth and convex with no definite lingual ridge and no developmental grooves.

The lingual height of contour is located at the middle third.

The cervical line lingually is slightly curved with the crest of curvature on the center of the root.

The lingual root is smooth convex with the apex directed distally . As the lingual root is narrower so buccal root outline appears from this aspect.

*In single rooted teeth, the root tapers till a pointed apex.

Mesial aspect :

* Geometric form:

It is trapezoidal in shape; however the longest of the uneven sides is toward the cervical portion and the shortest toward the occlusal portion.

*Outline:

The buccal outline of the crown is convex with the crest of curvature within the cervical third (The cervical ridge). It continues less convex to the tip of the buccal cusp. The tip of the buccal cusp is located directly below the center of the buccal root.


The lingual outline is curved smoothly from the cervical line to the tip of the lingual cusp. The crest of this curvature is near the center of the middle third.

The tip of the lingual cusp is on a line with the lingual border of the lingual root.

The lingual cusp is always shorter than the buccal cusp by about 1 m.m. The mesial marginal ridge is convex and is located at about the level of the junction of the middle and occlusal third.

The mesial contact area is circular in shape, located at the junction of the middle and occlusal thirds and slightly near the buccal.

The distinguishing features of this tooth from the mesial aspect are:

1- The canine fossa: The presence of the Mesial developmental depression which extends cervically from the contact area and continues up to include the cervical line then joins a deep developmental depression between the root bifurcation .

2- The mesial marginal developmental groove : The presence of well defined developmental grooves in the enamel of the


mesial marginal ridge. The marginal groove extend from the central groove of the occlusal surface of the crown, crossing the marginal ridge just lingual to the contact area and terminating a short distance cervical to the mesial marginal ridge. groove is called the

3- The root trunk is long on the distal than mesial. Thus the furcation on the mesial side is found on the middle third, while disatally in the apical third.

4- The mesial surface of the root trunk with a deep developmental groove and depression. In case of one rooted tooth, this depression is noticeable for most of the root length.

Distal aspect:

It resemble the mesial except for:

-The distal contact area is larger and more occlusally located than the mesial contact area and also slightly near to the buccal.

- The curvature of the cervical line is less on the distal than on the mesial surface ( it may be straight line).

-There is no deep developmental groove crossing the distal marginal ridge as in the mesial .

- The root trunk with no developmental depression.

- The bifurcation of the root is near the apical third .


Occlusal aspect

Geometrical outline: The occlusal aspect is roughly a six-sided or hexagonal figure (two equal buccal sides, Mesial side, shorter than distal and the mesiolingual is shorter than the distolingual side).

Outline:

It is wider buccolingually than mesiodistally.

Narrower lingually than buccally.

Elevations:

- The occlusal surface shows two well-developed cusps. The buccal cusp is larger than the lingual one.

Each cusp has distal cusp ridge and mesial cusp ridge. Also cusps triangular ridges extend from cusp ridge to the central groove oclussaly.

The buccal ridge descends from the cusp tip cervically onto the buccal surface.

Also there are two marginal ridges ( mesial and distal) found on both sides of the occlusal surface.

Depressions:

- Just inside the mesial and distal marginal ridges are the mesial and distal triangular fossae.

- The mesial and distal developmental pit are present on he depth of the triangular fossea..

- A well-defined central developmental groove divides the tooth mesiodistally. It extends from a point just mesial to the distal marginal ridge to the mesial marginal ridge where it joins the mesial


marginal developmental groove. This latter crosses the mesial marginal ridge and ends on the mesial surface of the crown.

Two grooves join the central groove extending on both sides of the mesial and distal triangular fossae. These are called the mesiobuccal and distobuccal developmental grooves.

* No supplemental grooves are present in most cases.

The pulp cavity

The buccolingual section

The pulp chamber is broad buccolingually with well developed pulp horns in its roof. The wide pulp chamber presents and leading into the root canals.

The premolars double rooted have two pulp canals. The single rooted could have one or two root canals. The lingual root canal is larger than the buccal. The root canals taper evenly from the floor of the pulp chamber to the apical foramen.

The Mesiodistal section : is similar to the pulp cavity of the maxillary canine. It is relatively narrow with an even taper from the pulp chamber to the root end.

A transverse section at the cemento-enamel junction shows the characteristic kidney shaped root trunk. The root form cervically is wider buccolingually than mesiodistally.


MAXILLARY SECOND PREMOLAR

The maxillary second premolar supplements the maxillary first premolar in function and resemble it except of the following variations:

� It is single rooted (85%) with less angular and rounded crown from all aspects.

� The crown of the second premolar is shorter cervico-occlusally. The root, however, is little longer.

� The maxillary second premolar is generally smaller in size comparing the maxillary first premolar.

Chronology

Appearance of dental organ 8 m .I.U.

First evidence of calcification 2- 2 years

Enamel completed 6-7 years

Eruption 10-12 years

Root completed 13-15 years

Buccal aspect

-The buccal cusp of the second premolar is shorter and appears less pointed.

-The mesial slope of the buccal cusp is usually shorter than the distal slope, which is the opposite for the first premolar.


Lingual aspect

The lingual cusp is almost the same length as the buccal cusp ( which differs than the first premolar).

Mesial aspect

-The buccal and lingual cusps are nearly the same length.

-There may be greater distance between the cusp tips which widens the occlusal surface buccolingually.

-The crown surface is convex with no developmental depression. Only a shallow developmental groove appears on the single tapered root.

-There is no deep developmental groove crossing the mesial marginal ridge.

Distal aspect

There is no variation noted except for the root variations.


Occlusal aspect

-The outline of the crown is more rounded or oval, rather than angular.

-There is a wide distance between the cusp tips buccolingually, and the lingual cusp is almost as wide as the buccal cusp.

-The central developmental groove is shorter mesiodistally and with multiple supplemental grooves radiating from the central groove.

-The mesial and distal triangular fossae are nearer to each other.

-The marginal ridges are thicker. .


THE PULP CAVITY

Buccolingual section

There is a wide pulp chamber with two well defined pulp horns.

There are two pulp canals, one buccal one lingual. The pulp cavity is very broad at its junction with the pulp chamber, then it narrows gradually until reaching the mid-root, then constricts rapidly to the apex.

A characteristic feature of the pulp cavity from this section is that it may show single broad pulp canal divided at mid-root into two canals by Dentin Island, and then the canals join again near the apical foramen.

Mesiodistal section

Similar to that of the maxillary first molar.

Cervical cross section

A cervical cross section may display an oval root trunk instead of the kidney shaped root trunk of the first premolar.


upper premolars (2)

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