The Permanent Maxillary Premolars

A. Introduction:

Maxillary premolars possess a number of general characteristics which aid in differentiating them from other posterior teeth, especially from the premolars in the mandibular arch.

1. Maxillary first and second premolars are much more similar to each other than are the mandibular premolars.

2. In the maxillary arch, the first premolar is generally a little larger than the second premolar, while in the mandible the first premolar is considerably smaller.

3. The crowns of maxillary premolars are normally wider buccolingually than mesiodistally, while the mandibular premolars' buccolingual and mesiodistal crown dimensions are approximately equal.

4. Maxillary premolars possess two cusps of nearly equal size. The mandibular premolars may have more than two cusps, and the lingual cusps are normally less prominent than the facial cusps.

5. When viewed from either proximal surface, the crown profile of the maxillary premolars shows virtually no lingual inclination, and thus is pretty much centered over the root. In contrast, the crowns of the mandibular premolars are heavily inclined and offset toward the lingual.

6. The maxillary first premolar is the only premolar which normally exhibits two root branches.

B. The Permanent Maxillary First Premolar:

1. General characteristics:

a. Arch position - The maxillary first premolar is the fourth permanent tooth from the midline. It has a mesial contact with the permanent maxillary canine, and a distal contact with the second premolar. It replaces the deciduous maxillary first molar, and hence is a succedaneous tooth.

b. Universal number:

Maxillary right first premolar - #5 Maxillary left first premolar - #12

c. General form and function - The outline from the occlusal aspect roughly resembles a hexagonal, or six-sided figure, while the general shape from the proximal aspects is trapezoidal. From the facial aspect, the shape is pentagonal and quite similar to that of a maxillary canine. The first premolar exhibits two very similar cusps, plus two root branches in the majority of specimens.

In mastication, the first premolar functions basically as a grinding tooth, and contributes to the esthetics and phonetics roles as well.

2. Development Table: (Maxillary first premolar)*

Initiation of calcification 11/2-13/4 yrs.

Completion of enamel 5-6 yrs.

Eruption 10-11 yrs.

Completion of root 12- 13 yrs.

Buccal aspect:

a. General considerations - From the facial aspect, the pentagonally shaped crown bears a close resemblance to those of both the maxillary canine and second premolar. However, the canine crown is somewhat larger in size, with a more prominent cusp tip, and the crown of the second premolar is smaller, with a less prominent cusp tip. The occlusocervical dimension of the crown is less than for any anterior tooth, but greater than that of the second premolar or any molar.

b. Mesial margin - The mesial margin joins the mesio-occlusal slope to create an obtuse mesio-occlusal angle. The contour of the mesial outline is shallowly concave from the contact area to the cervical line. The crest of curvature at the contact area is located near the junction of the occlusal and middle thirds.

c. Distal margin - The distal is slightly shorter, but otherwise is much the same as the mesial margin, but the disto-occlusal angle is a little less prominent, and the cervical concavity is not as deep. The crest of curvature is also slightly more cervically located.

d. Occlusal outline - The occlusal margin of this tooth is, similar to the incisal margin of the maxillary canine. The facial cusp tip is pronounced, although it is not as prominent as is the maxillary canine's. The cusp tip divides the occlusal outline into two unequal portions. The mesio-occlusal slope is longer and straighter, while the disto-occlusal slope is shorter and more curved. The cusp tip is thus offset slightly toward the distal. This relationship of the occlusal slopes normally exists prior to attrition, and of course wear may alter it.

Occasionally, the developmental depressions pass over the occlusal margin, with a resultant concavity, or notch in the outline of each of the occlusal slopes.

e. Cervical outline - The CEJ is evenly convex toward the apex, but the depth of curvature is generally less than that found in the anterior teeth.

f. Other considerations - The most notable feature on the buccal surface is the buccal ridge. It extends about halfway along the surface from the tip of the buccal cusp toward the cervical line, and is the result of the greater development of the middle buccal lobe. It is comparable to the labial ridge of the canines.

Mesiobuccal and distobuccal developmental depressions are present on each side of the buccal ridge, and appear to divide the occlusal portion of the buccal surface into vertical thirds, corresponding to the three buccal lobes. In the cervical third of the surface, imbrication lines are also a common finding.

The height of contour is located in the cervical third of the surface. Lingual aspect:

a. General considerations - The lingual surface of the crown is smoothly convex in all directions. There is no clearly defined lingual ridge.

The crown tapers toward the lingual, so the tooth is narrower mesiodistally at the lingual than at the buccal. In fact, the lingual surface is smaller than the buccal surface in all dimensions.

Since the lingual cusp is shorter than the buccal cusp, the tips of both are visible from the lingual aspect. However, the two cusp tips do not fall on the same line, since the lingual cusp tip is noticeably offset to the mesial, which is opposite to the distal placement of the buccal cusp tip.

b. Mesial and distal outlines - The proximal outlines are normally somewhat convex, and shorter than the same outlines of the buccal surface. However, the mesial outline may be concave if the mesial concavity is severe.

c. Occlusal outline - The lingual cusp tip is not as sharply pointed as the buccal cusp tip. It is offset toward the mesial, making the mesio-occlusal slope shorter than the disto-occlusal slope. It is shorter than the buccal cusp, usually by as much as one millimeter, or occasionally even more. In fact, it is the shortest of the four maxillary premolar cusps.

d. Cervical outline - The cervical line is curved symmetrically toward the apex.

e. Other considerations - No developmental depressions, grooves, or pits are normally found on this surface.

The lingual height of contour is normally located in the middle third. Mesial aspect:

a. General considerations - The general shape of the mesial surface is trapezoidal, with the longer parallel side located at the cervical.

b. Buccal margin - The buccal outline is generally convex, with the height of contour in the cervical third.

c. Lingual margin - Lingually, the outline takes the form of an even arc, with the height of contour in the middle third.

d. Occlusal margin - The occlusal margin is irregularly concave, and the majority of it is made up of the mesial marginal ridge. A prominent mesial marginal groove is usually present indenting the occlusal margin almost two-thirds of the way from the buccal to the lingual outline.

e. Cervical margin - The cervical line is most often irregularly convex toward the occlusal, due to the mesial concavity, but on occasional specimens it has an even convexity. The depth of curvature is less than that found on any anterior tooth except the distal of the canine, where the two are equal.

f. Other considerations - From this aspect, it is easy to observe the difference in height between the two cusp tips.

Mesial concavity - A unique feature of the mesial surface of the maxillary first premolar is the mesial concavity. This depressed area is variable in its extent. Most often, it is limited to the middle portion of the cervical third, but some specimens exhibit an extension which may reach as far as the middle portion of the mesiobuccal line angle area. This landmark is a relatively consistent way to distinguish the maxillary first premolar from the second premolar, which usually lacks it.

The mesial height of contour is associated with the contact area, near the junction of the middle and occlusal thirds. The contact area is roughly circular in shape and is offset to the buccal.

Distal aspect:

a. General considerations - The distal is remarkably similar to the mesial surface, although it is slightly shorter occlusocervically.

b. Buccal margin - The buccal outline is convex throughout its length, with the crest of curvature in the gingival third.

c. Lingual margin - The lingual margin is almost symmetrical, and is quite convex, especially in the middle third, where the height of contour is located.

d. Occlusal margin - Occlusally, the distal is similar to the mesial aspect, except that the marginal ridge is located at a more cervical level, allowing more of the occlusal surface to be visible. There is normally no marginal groove. In the rare instances when it is present, it is indistinct.

e. Cervical margin - The curvature occlusally is less than on the mesial.

f. Other considerations - The distal contact area is larger than the mesial, and is located at a slightly more cervical level, but still at the junction of the occlusal and middle thirds. Its outline is ovoid, and is wider buccolingually than occlusogingivally.

The distal surface is generally convex in all directions, and does not exhibit the concavity which is present on the mesial surface, although there may sometimes be a flattening in the same area.

Occlusal aspect:

a. General considerations - From the occlusal aspect, the outline of the crown can be described as hexagonal, or six-sided, and it is wider buccolingually than mesiodistally.

b. Buccal outline - The prominent buccal ridge is the primary contributor to the generally convex buccal outline. If the buccal developmental depressions are deep, they may create slight concavities in the outline on either side of the buccal ridge.

c. Lingual margin - The lingual margin is evenly convex, almost in a semicircle.

d. Mesial and distal margins - The two proximal margins are relatively straight, and they converge toward the lingual. Thus, the lingual portion of the tooth is narrower mesiodistally than the buccal portion. When the mesial marginal groove is prominent, it may create a dip in the mesial outline.

e. Boundaries - The occlusal surface, or occlusal table, is bounded on the mesial and distal by the marginal ridges, and on the buccal and lingual by the mesial and distal cusp ridges of the buccal and lingual cusps.

Components of the Occlusal Table:

a. Cusps - There are two cusps, named by location, buccal and lingual. The buccal cusp is normally sharper, longer, and bulkier.

i. Buccal cusp - The buccal cusp tip is located well toward the buccal, and is offset to the distal. It is wider and higher than the lingual cusp. The buccal cusp has four cusp ridges, and they are named according to the direction they extend from the cusp tip:

Buccal cusp ridge - The buccal cusp ridge extends cervically from the cusp tip on the buccal surface, and corresponds to the previously described buccal ridge.

Lingual cusp ridge - It extends lingually from the cusp tip to the central groove. This cusp ridge is also one of two triangular ridges found on the tooth, so it can be said that the lingual cusp ridge of the buccal cusp is synonymous with the buccal triangular ridge of the tooth. In addition, it may be called the buccal portion of the transverse ridge. Mesial cusp ridge - The mesial cusp ridge extends mesially from the cusp tip to the mesiobucco-occlusal point angle area.

Distal cusp ridge - It extends distally from the cusp tip to the distobucco-occlusal point angle area. The mesial and distal cusp ridges correspond to the mesio-occlusal and disto-occlusal slopes, which compose the occlusal outline, when the tooth is viewed from the buccal aspect.

Lingual Cusp Ridge

Inclined Planes and Cusp Ridges of a Buccal Cusp (premolar)

The buccal cusp has four inclined planes, which are the sloping areas located between two adjacent cusp ridges. They take the name of the two cusp ridges which they lie between, as follows: Mesiobuccal inclined plane (non-functional)

Distobuccal inclined plane

(non-functional) Mesiolingual inclined plane

(functional) Distolingual inclined plane (functional)

In active occlusion, the buccal cusps of the maxillary posterior teeth are functional only on their lingual side. Hence, the only functional inclined planes of the buccal cusp are those on the lingual, the mesiolingual and the distolingual.

ii. Lingual cusp - The lingual cusp tip is located well to the lingual, and is offset toward the mesial. It is generally smaller and rounder than the buccal cusp. It is the shortest of all the maxillary premolar cusps. It also has four cusp ridges and four inclined planes, which are located and named in the same manner as those of the buccal cusp. Since the lingual cusp is in function on both buccal and lingual sides, it would seem that all four of its inclined planes would be functional. However, as will be pointed out in the next unit, the entire lingual cusp of the mandibular first premolar is normally non-functional. This means that because of the normal manner by which the first premolars of the two arches occlude, the mesiolingual inclined plane of the lingual cusp of the maxillary first premolar is not in function. Therefore, this tooth has only three functional inclined planes associated with its lingual cusp rather than the expected four.

b. Transverse ridge - The buccal and lingual triangular ridges of the tooth meet in the area of the central groove, thus forming a transverse ridge.

c. Marginal ridges - Unlike the marginal ridges of anterior teeth, those of posterior teeth form the mesial and distal borders of the occlusal surface. They are linear ridges which run from the bucco-occlusal point angle to the linguo-occlusal point angle, and are named mesial and distal marginal ridges by their location. The mesial marginal ridge is normally slightly shorter, and its continuity is interrupted by the mesial marginal groove near its midpoint.

d. Fossae - Fossae are the general depressed areas on the occlusal surfaces of posterior teeth, and the maxillary premolars normally display two of them.

i. Mesial triangular fossa - This fossa is roughly triangular in shape, and is bounded by the mesial marginal ridge, the transverse ridge, and the mesial cusp ridges of the two cusps.

M ii. Distal triangular fossa - It has a shape and boundaries which are similar to those of the mesial triangular fossa, although it is not quite so deep.

e. Pits and Grooves:

The occlusal surface of the maxillary first premolar normally exhibits two pits, which are located in the deepest portion of the two fossae. They are named by location:

i. Mesial pit - The mesial pit is located in the mesial triangular fossa just inside the mesial marginal ridge about midway buccolingually. The mesial pit is the point of union of four primary or developmental grooves:

Mesiolingual triangular groove - This groove extends a short distance from the mesial pit in a mesiolingual direction, where it fades out.

Mesiobuccal triangular groove - It is similar to the ML triangular groove, except that it runs in a mesiobuccal direction.

Central groove - The central groove has a mesiodistal direction and connects the mesial pit and the distal pit.

Mesial marginal groove - The mesial marginal groove extends from the mesial pit in a mesial direction, crossing over the marginal ridge a short distance onto the mesial surface, where it fades out.

ii. Distal pit - The distal pit is located just inside the distal marginal ridge, midway buccolingually, and is the point of union of three primary grooves:

DB triangular groove PL triangular groove Central groove se^ar,

Note: All the grooves described are primary or developmental grooves. Other grooves are sometimes present, as well, and they are normally not given a specific name. They are simply known as supplemental or secondary grooves. On this tooth, the most consistent and easily observable secondary grooves are those which outline the triangular ridges on their mesial and distal borders. This is true of other posterior teeth as well. The maxillary first premolar normally has less secondary grooves than the second premolar.

Distolingu Triqnguloi Groove

Distal Pit

Distolingu Triqnguloi Groove

Distal Pit

Secondary Grooves

Pits and Grooves of Maxillary Right First Premolar

Secondary Grooves

Pits and Grooves of Maxillary Right First Premolar

The root structure of the maxillary first premolar is unique among premolars, since there are two branches in a majority of cases, while all other premolars are normally single rooted. Even though two roots are most commonly found in this tooth, there are three identifiable root types, as follows:

The single root is quite straight, and tapers fairly evenly from the cervical line to an apex which is rather blunt. It is wider buccolingually than mesiodistally. Both buccal and lingual surfaces are convex, and the buccal portion of the root is slightly wider than the lingual.

The mesial concavity of the crown is usually continuous with a concavity sj forming a longitudinal groove, or root concavity on the mesial surface of the root. A longitudinal groove is often found on the distal surface as well, but it is not normally as pronounced. Therefore, both mesial and distal surfaces are normally concave, but the mesial surface is much more so.

In cross section at mid root, the outline is most often somewhat kidney shaped. The buccal and lingual outlines are convex, but the mesial surface is quite indented, reflecting the mesial root concavity. The distal surface is flat to slightly concave.

b. Type II - Bifurcated root:

The root trunk divides into a buccal and a lingual root branch. Root trunk is defined as that portion of the root situated between the cervical line and the point of furcation (branching). Thus, a root trunk is found only in multirooted teeth. A type II root is usually bifurcated for at least half its length.

All surfaces of both root branches are convex, and taper to apices which are sharp. The buccal root branch is normally larger in general size, although the two roots are about equal in length.

In cross section at the mid root level, both branches are more or less round in outline, with the buccal root outline slightly greater in circumference. This is the most common root form of maxillary first premolars.

c. Type III - Laminated root:

This type resembles Type II, except the buccal and lingual branches are M joined wholly, or in part, by a lamination, which is defined as a thin connection between the main portions of the root structure.

Many variations of the laminated type may be found. The typical hourglass outline of a mid root cross section is similar in all respects to that of the single root, except for the distal outline which is greatly indented, or concave, like the mesial outline, thus leaving a thin connection, or lamination, between the two portions.

TYPE III

10. Variations and anomalies:

a. Crown form generally does not differ widely, although the mesial concavity exhibits considerable variability in its area and depth.

b. Root form is variable, as evidenced by the three common types. Deflected roots and abnormal curvatures are fairly common. Occasionally, a three rooted specimen is found, with two buccal branches, and one lingual branch.

c. The root(s) may, on rare occasions, penetrate the anterior portion of the maxillary sinus, also known as the antrum.

The Permanent Maxillary Second Premolar: 1. General characteristics:

a. Arch position - The permanent maxillary second premolar is the fifth tooth from the midline. It shares a mesial contact with the maxillary first premolar and a distal contact with the maxillary first molar. It is a succeda-neous tooth, replacing the deciduous maxillary second molar.

b. Universal number:

Maxillary right second premolar - #4 Maxillary left second premolar - #13

c. General form and function - The two maxillary premolars are functionally alike. Structurally, the second premolar closely resembles the first premolar, with some general exceptions:

i. The crown of the second premolar is slightly smaller in all dimensions than that of the first premolar.

ii. The second premolar is generally less blocky, thus exhibiting a more rounded crown form.

iii. The buccal and lingual cusps are of nearly equal height in the second premolar.

iv. There is normally no mesial concavity or marginal groove found on the crown of the second premolar.

v. The second premolar is normally a single rooted tooth.

vi. More variations from normal are observed with second premolar specimens.

2. Development Table: (Maxillary second premolar)*

Initiation of calcification 2 to 2 1/4 years

Completion of enamel 6 to 7 years

Eruption 11 to 12 years

Completion of root 12 to 14 years

3. Buccal aspect:

The buccal aspect is similar to that of the maxillary first premolar, with the following exceptions:

a. The buccal cusp of the second premolar is not as long or pointed.

b. The cusp tip is offset to the mesial, thus the mesio-occlusal slope is M slightly shorter than the disto-occlusal slope. The reverse is true of the first premolar.

c. The mesio-occlusal and disto-occlusal line angles are not as prominent, and the mesial outline is not quite so concave.

4. Lingual aspect:

The lingual aspect is similar to that of the maxillary first premolar, with the following exceptions:

a. The lingual cusp is relatively longer, making the crown longer on the lingual side, and so less of the occlusal surface is visible from this aspect.

D b. The lingual cusp tip is not quite so far offset to the mesial.

5. Mesial aspect:

The mesial aspect is similar to the mesial of the maxillary first premolar, with the following exceptions:

a. The two cusps are nearly the same length.

b. There is no mesial concavity, and instead this portion of the crown is slightly flattened or convex.

c. A mesial marginal groove is usually absent.

d. Both the contact area and marginal ridge are located at a slightly more cervical level than on the mesial of the first premolar.

6. Distal aspect:

The distal aspect is similar to that of the maxillary first premolar, with the following exceptions:

a. The two cusps are approximately the same length.

b. The contact area is slightly larger in size, when compared to the first premolar, since the second premolar's distal contact is with the first molar.

c. Both the distal contact area and marginal ridge are found at a slightly more cervical level than on the distal of the first premolar.

7. Occlusal aspect:

The occlusal aspect differs from the maxillary first premolar in the following ways:

a. The line angles of the crown are more rounded, and consequently the crown appears less angular. This makes the hexagonal outline more difficult to visualize.

b. The central groove is often shorter, and may be more irregular, sometimes displaying multiple supplemental grooves. Because of the shorter central groove, the mesial and distal pits are located closer to each other and more to the middle of the occlusal table.

c. The mesial marginal groove is normally absent, but even if present, it is quite indistinct.

d. The lingua] cusp tip is normally not quite as far offset to the mesial.

e. On the lingual cusp, there are four functional inclined planes, whereas the first premolar exhibited only three.

a. The root is normally single, and tapers rather evenly from the cervical line to a relatively blunt apex.

b. Root length is normally as great, or slightly greater, than the root structure of the first premolar.

c. The root is wider buccolingually than mesiodistally, with the buccal portion slightly wider mesiodistally than the lingual. Buccal and lingual

M surfaces are convex, and mesial and distal surfaces are either convex or flat.

d. In cross section views, the root outline is normally ovoid, or a flattened ovoid, wider buccolingually.

e. It is often deflected slightly to the distal in its apical portion. Variations and anomalies:

a. Crown form varies more than in the first premolar. A central groove may be absent, so that only one centrally located pit is present on the occlusal surface.

b. Root variations occur, and distal deflections of the apical third are not uncommon. On occasion, there are two roots, buccally and lingually positioned, similar to those of the type II first premolar.

c. As with the other maxillary posterior teeth, the root occasionally penetrates the antrum.

Maxillary Right First Premolar

OCCLUSAL

Maxillary First Premolar Root Variations Mesial View

Bifurcated mm

Bifurcated

Mid-Root Section

Maxillary Right Second Premolar

I. Reading Assignment:

Unit # 6 (The Permanent Mandibular Premolars)

II. Specific Objectives:

At the completion of this unit, the student will be able to:

A. List the appropriate age(s) concerning developmental chronology of the mandibular premolars found in the development tables, or select the appropriate age(s) from a list, when given a certain developmental feature. The student should also be able to compare these ages between the mandibular premolars.

B. Demonstrate a knowledge of the morphology of each surface of the crown, as well as the root, of each permanent mandibular premolar by:

1. describing,

2. selecting the correct information from a list,

3. or interpreting a diagram to identify or name any of the following features:

a. Contours of any surface or margin of any surface.

b. Structural entities such as grooves, pits, ridges, inclined planes, cusps, fossae, lobes etc.

c. Height of contour and contact areas.

d. Relative dimensions and shape.

e. Any other surface feature.

Furthermore, the student will be able to make comparisons of any of these features between the mandibular premolars.

C. Make comparisons between mandibular premolars, and other permanent teeth, where appropriate, by selecting the correct response from a list.

D. Make comparisons between the general characteristics of the mandibular premolars, including function, arch position, distinguishing features, etc., by describing them, or selecting the correct response from a list, when given the tooth (teeth), or a description of the general characteristic(s).

E. Determine from a diagram or description whether a given mandibular premolar is first or second, or right or left.

F. Determine the correct universal number, or Palmer notation, for a given diagram or description of any mandibular premolar.

G. Demonstrate a knowledge of any of the new terms in this unit by defining them, or selecting the correct definition or application thereof from a list, when given the term, or any of its applications.

H. Demonstrate a knowledge of any of the variations or anomalies in this unit by describing them, or selecting the correct response from a list, when given the particular tooth (teeth), the anomaly, or any of its features or applications.

The student is also responsible for any material which was to have been mastered in previous units.

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