The Permanent Maxillary Incisors

A. Introduction:

When compared to the mandibular incisors, those in the maxillary arch have crowns which are generally larger in all dimensions, but especially mesiodistally. The crown area of the maxillary central incisor is normally much greater than that of the maxillary lateral incisor. The lateral incisor crown is similar in form to the crown of the central incisor, only on a smaller size scale in all dimensions.

B. Permanent Maxillary Central Incisor:

1. General characteristics:

a. Arch position - The maxillary central incisors are the two teeth which are adjacent to the midline in the upper arch. They share a mesial contact area with each other, and have a distal contact with the lateral incisors.

b. Universal number: Maxillary right central incisor - #8 Maxillary left central incisor - #9

c. General form and function - As viewed from the labial or lingual aspects, the crown is trapezoidal in shape, and the widest mesiodistally of any anterior tooth. As viewed from either proximal aspect, the crown is triangular in shape. The general crown size exceeds that of any other incisor in either arch.

The central incisors' functions in mastication are biting, cutting, incising and shearing. They also play an important role in the esthetics and phonetics functions of the human teeth.

2. Development Table: (Maxillary central incisor)*

Initiation of calcification 3 to 4 months

Completion of enamel 4 to 5 years

Eruption 7 to 8 years

Completion of root 10 years

3. Labial aspect (of the crown):

a. General considerations - The basic geometric shape of the labial surface is trapezoidal, with the longer parallel side at the incisal, and the shorter side at the cervical. Although the crown is longer (incisocervically) than it is wide (mesiodistally), these two dimensions are more nearly equal than for any other permanent incisor. In the maxillary lateral, and even more so in the mandibular incisors, the crown is considerably longer than it is wide.

The labial surface is generally convex in both dimensions, mesiodistally M and incisogingivally. The convexity is normally greatest in the cervical third, and tends to more closely approach flatness toward the incisal third.

b. Mesial outline (margin) - The mesial outline of the crown is slightly convex but can be nearly straight, with the crest of curvature at the contact area in the incisal third near the mesioincisal angle. The mesioincisal angle is rather sharp.

c. Distal outline - This outline is also convex, but more rounded than on the mesial, as is the distoincisal angle. The crest of curvature is associated with the contact area, which is located in the incisal third very near the junction of the incisal and middle thirds, and so is farther cervically than it is on the mesial. Although the cervical half of the mesial and distal outlines is normally convex, either outline can be nearly straight, in comparison to the almost always convex incisal half.

d. Incisal outline - The incisal outline may exhibit mamelons. Without mamelons, the outline is generally straight, and nearly perpendicular to the long axis of the tooth.

e. Cervical margin (or CEJ) - The CEJ curves evenly toward the root. The crown is narrower mesiodistally at the cervical margin than at the incisal.

f. Other considerations:

Developmental depressions - Two straight, shallow depressions, which extend from the incisal edge toward the gingival, and fade out in the middle third. They are termed, mesiolabial and distolabial developmental depressions. and as has already been pointed out, they represent the division of the three labial lobes.

Imbrication lines - Faint, curved lines which roughly parallel the CEJ in the cervical third of the surface. They are not always present. Height of contour - The height of contour of the labial surface is located in the cervical third.

Lingual aspect:

a. General considerations - The lingual surface is also roughly trapezoidal. It is slightly narrower mesiodistally than is the labial, since both mesial and distal surfaces converge slightly toward the lingual, a feature which is also true of all other anterior teeth. It has both convexities and a concavity. The incisal half to two-thirds of the surface is a large, usually shallow, concavity, termed the lingual fossa, while the convex structure in the cervical portion is known as the cingulum.

b. Mesial and distal outlines - These two margins are similar to their labial counterparts, except that they converge slightly more toward the gingival.

c. Incisal margin - The incisal margin is also similar to that of the labial aspect.

d. Cervical margin - The cervical outline has a slightly greater depth of curvature apically than on the labial surface, and is asymmetrical, with its area of maximum curvature offset to the distal.

Maxillary Central Incisor Labial View

Maxillary Central Incisor Labial View

Imbrication Lines

Labial

Developmental Depressions

Mamelons

Imbrication Lines

Labial

Developmental Depressions

Mamelons e. Other considerations:

Lingual fossa - The lingual fossa is the shallow concavity found in the incisal half to two-thirds of the crown, which includes the largest area of the lingual surface. It. is bounded by four convexities; on the mesial and distal by the mesial and distal marginal ridges, on the incisal by the incisal edge, and on the cervical by the cingulum. The fossa is most often smooth. However, there are occasionally rather poorly defined ridges which extend into the cervical portion of the lingual fossa from the cingulum. When present, these ridges may form a "W" shaped pattern. Cingulum - The cingulum is the bulky convexity located in the cervical portion of the lingual surface. It is generally smooth. Sometimes there is a groove, the linguogingival groove, which separates the cingulum and the lingual fossa. On occasion, there may also be a lingual pit located between the cingulum and fossa. The pit may be found near the center of the linguogingival groove, if that structure is present. The linguogingival groove and lingual pit are much more commonly found on maxillary laterals than on maxillary centrals. However, neither structure is a usual finding on the crown of any permanent incisor.

Marginal ridges - The marginal ridges mark the mesial and distal borders of the lingual fossa, as well as the lingual surface. They are linear, and extend from their respective incisal angles to the cingulum. They are named, by location, mesial and distal marginal ridges.

Height of contour - The lingual crest of curvature is located in the cervical third, at the greatest convexity of the cingulum.

Mesial aspect:

a. General considerations - From this aspect, the central incisor crown is roughly triangular in shape, and the incisal edge, at the apex of the triangle, lies over the long axis of the tooth. The mesial surface is generally convex in both dimensions, incisocervically and labiolingually.

b. Labial outline - The labial outline is convex, with the height of contour and the greatest convexity located in the gingival third. Some specimens may exhibit a flat outline incisal to the crest of curvature.

c. Lingual outline - The lingual margin is somewhat concave in the incisal portion, and convex in the gingival portion, due to the respective contours of the lingual fossa and cingulum. The entire outline may be described as a shallow "S". The crest of curvature of the lingual outline is found in the cervical third at the prominence of the cingulum.

d. Cervical margin - The CEJ curves evenly toward the incisal. It exhibits the greatest depth of curvature of any tooth surface in the mouth.

e. Incisal outline - It is usually pointed, or slightly rounded, in newly erupted incisors, due to the convergence of the labial and lingual surfaces. In teeth with incisal wear, the outline is straight, but slopes from labial to lingual.

Incisai Ridge

Newly Erupted

Incisor

Older Maxillary

Incisor

Incisai Ridge

Incisai Edge'

Newly Erupted

Incisor

Older Maxillary

Incisor

Older Mandibular

Incisor

Before proceeding, the difference between two similar terms should be clarified. The incisal ridge is the projection of enamel on newly erupted teeth, which is the incisal termination of the tooth. In a proximal view, it is normally pointed, or slightly rounded. After the tooth enters into occlusion, this ridge is blunted and flattened, resulting in a sloping, straight outline from the proximal aspect. This flattened area is termed the incisal edge.

f. Other considerations:

Height of contour - The mesial height of contour is located in the incisal third at the contact area.

Contact area - The mesial contact area is located in the incisal third, near the incisal margin, and is centered labiolingually. It is roughly ovoid, long incisogingivally, and narrow labiolingually. It is the only proximal area in the maxillary arch where mesial surface contacts mesial surface.

The distal surface closely resembles the mesial surface, with the following exceptions:

a. The distal surface is generally smaller than the mesial surface, because the incisocervical dimension is shorter.

b. The distal surface is more convex incisogingivally.

c. The cervical margin does not curve as far incisally.

d. Because it contacts the lateral incisor, which is a smaller tooth, the distal contact area is accordingly smaller in size. Its shape is still ovoid, but it is more nearly round than on the mesial. It is also located farther gingivally, still in the incisal third, but very near the junction of the incisal and middle thirds.

7. Incisal aspect:

a. From the incisal aspect, the central incisor's outline is roughly triangular. The incisal edge is relatively straight mesiodistally, and is roughly centered over the root. From this aspect, it can be seen that the lingual surface is narrower mesiodistally than the labial surface. It is also apparent that this tooth and its incisal edge are the widest mesiodistally of any of the permanent incisors.

M

b. The labial and lingual outlines are convex to differing extents. The labial outline is only slightly convex, while the lingual outline is quite convex, due to the prominence of the cingulum. The labial line angles are more distinct than the lingual line angles. Portions of the lingual fossa and cingulum are visible. Most often, the greatest contour of the cingulum is offset to the distal.

M a. The root is single, conical, relatively straight, and tapers to a rounded apex.

b. A horizontal cross section of the root near the cervical line shows a rounded triangular outline. Normally, the root is wider at the labial, which is the base, of the triangle, and narrower at the lingual which is the apex. A mid root cross section usually reveals a somewhat ovoid outline, which is wider labiolingually than mesiodistally. I c. The root length is approximately one and a half times the crown length.

9. Variations and Anomalies:

a. Of all the crown surfaces, the lingual exhibits the greatest variation. As previously mentioned, a pit may occasionally be present, and the depth of the fossa has a considerable range.

b. When viewed from the labial or lingual aspects, a wide variation occurs in the amount of convergence of the mesial and distal surfaces toward the cervical. When there is little convergence, the outline of the surface resembles a rectangle, but when great convergence is present, it is more nearly triangular.

c. Root length may vary considerably, but deflections of the root are relatively rare. When the root is exceptionally short, in conjunction with an abnormal contour of the crown, this anomalous condition is referred to as dwarfed root, and the lack of root support may endanger the tooth's longevity in the mouth.

d Hutchinson's incisors - Congenital syphilis sometimes manifests itself in the central incisor by producing a screwdriver shaped crown, when it is viewed from the labial aspect.

e. Talon cusp - A large accessory cusp on the lingual surface of maxillary incisors characterizes this anomaly. Involved teeth often bear a resemblance to a Phillips screwdriver.

f. The alveolar bone between the roots of the two central incisors is occasionally the site of supernumerary teeth, or extra teeth, known as mesiodens. Cysts may also be found in this area.

C. Permanent Maxillary Lateral Incisor: 1. General characteristics:

a. Arch position - The maxillary lateral incisor is the tooth in each maxillary quadrant of the permanent dentition which is second from the midline. Contact is shared with the permanent central incisor on the mesial, while the distal contact is with the deciduous canine until its exfoliation at about age 12, and then with the permanent canine.

b. Universal number:

Maxillary right lateral incisor - #7 Maxillary left lateral incisor - #10

c. General form and function - The lateral incisor supplements the central incisor in function.

It resembles the central incisor in all aspects, but on a smaller scale. In fact, it is smaller in all measurements, except root length, which is roughly the same. Its relative crown dimensions, and hence its shape, differ slightly from the central, however. It is relatively longer incisocervically and narrower mesiodistally. It also is generally a more round tooth than the central incisor.

The upper lateral incisors display greater variation in form than any other permanent tooth, except the third molars. Development Table: (Maxillary lateral incisor)*

Initiation of calcification 1 year

Completion of enamel 4 to 5 years

Eruption 8 to 9 years

Completion of root 11 years

Labial aspect:

a. Mesial outline - This margin resembles that of the central incisor, but usually is more convex and has a more rounded mesioincisal angle. The crest of curvature, at the contact area, is located farther gingivally in the incisal third, quite near its junction with the middle third.

b. Distal outline - The distal margin is always more rounded than the distal outline of the central incisor, with a more cervically placed crest of curvature, usually at the junction of the incisal and middle thirds. The distoincisal angle is noticeably more rounded than its central incisor counterpart, and also more rounded than its own mesioincisal angle. In fact it is the most rounded incisal angle of any incisor in either arch.

c. Incisal outline - The incisal outline resembles the central incisor, but it is not so straight, partially because of the greater rounding of the two incisal angles. It exhibits the greatest rounding of any incisor. The number and prominence of mamelons is variable, but two are the most common finding.

d. Cervical outline - The cervical line curves in a regular arc apically, with only slightly less depth than in the central incisor.

e. Other considerations - The labial surface itself is more convex both mesiodistally and incisogingivally than the maxillary central.

Labial developmental depressions and imbrication lines are often present, similar to those of the central incisor.

The labial height of contour is located in the cervical third.

Lingual aspect:

a. Mesial margin - The mesial outline is similar to that of the central incisor.

b. Distal margin - This margin is also similar to its central incisor counterpart, and the distoincisal angle is much more rounded than is the mesioincisal angle.

c. Incisal outline - The incisal margin is similar to the labial aspect.

d. Cervical outline - The CEJ curves toward the apical, but is offset to the distal.

e. Other considerations:

The mesial and distal marginal ridges, as well as the cingulum, are relatively more prominent, and the lingual fossa is deeper, when compared to the same structures of the central incisor.

A linguogingival groove is a more common finding in maxillary lateral incisors than in central incisors. A lingual pit, near the center of this groove, is also more common, and when present, is a potential site for caries. Another groove, which is sometimes found on the lateral, but very rarely on the central incisor, is the linguogingival fissure. This groove usually originates in the lingual pit and extends cervically, and slightly distally, onto the cingulum. It might be helpful to think of the linguogingival fissure as running in a more or less vertical direction, while the linguogingival groove extends in a roughly horizontal direction.

Incisai Edge

Mesial

Marginal

Ridge

Incisai Edge

Mesial

Marginal

Ridge

'Cingulum

The height of contour is associated with the greatest curvature of the cingulum in the cervical third. Mesial aspect:

a. The mesial aspect is very similar to the central incisor, with lessened dimensions.

b. The contact area is also similar in shape to the contact of the central incisor. It is found in the incisal third very near the junction of the incisal and middle thirds.

c. The cervical line exhibits less depth of curvature than it does on the mesial of the central incisor.

Distal aspect:

a. The distal surface is smaller and more convex in all dimensions than the mesial surface.

b. The contact area is shorter and not as incisally placed, when compared to the mesial contact. It is normally located at the junction of the incisal and middle thirds.

c. The cervical line shows less curvature incisally than on the mesial surface. ,

Incisal aspect:

a. From the incisal aspect, the lateral generally resembles the central incisor. except the cingulum is often more prominent.

b. The lateral incisor also exhibits relatively more convexity labially and lingually than the central incisor, and its outline may approach the rhom-bo appearance of the canine.

a. The lateral incisor root is single, and wider labiolingually than mesiodistally.

b. In comparison to the central, the root is longer in relation to the crown length. In actual length, the root is the same length or slightly shorter than that of the central.

c. The apex is relatively sharper than that of the central, and the apical third may be deflected, and if so it is most often toward the distal.

d. In both cervical and midroot cross sections, the outline is roughly ovoid, wider labiolingually than mesiodistally. The labial dimension is wider mesiodistally than is the lingual.

9. Variations and Anomalies:

a. The incisal portion of the cingulum may exhibit a tubercle.

b. The previously described linguogingival fissure may extend all the way onto the root surface from the adjacent cingulum.

c. Distorted crowns and unusual root curvatures are more commonly seen than with any other incisor.

d. Peg lateral - A diminutive peg-shaped crown form, which is relatively common, and is due to a lack of development of the mesial and distal eg Crown portions of the crown.

e. Maxillary laterals sometimes are congenitallv missing, i.e.: tooth buds do not form (agenesis).

f. The lingual pit of the maxillary lateral may be the entrance site where — enamel and dentin have become invaginated in the tooth's pulp cavity, due to a developmental aberrancy called dens in dente.

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  • Jackson
    Are marginal ridge of maxillary centrals sharper than maxillary laterals?
    2 days ago

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