Detailed Description of the Maxillary Lateral Incisor From All Aspects
Labial Aspect
Although the labial aspect of the maxillary lateral incisor may appear to favor that of the central incisor, usually it has more curvature, with a rounded incisal ridge and rounded incisal angles mesially and distally (see Figures 6-13 and 6-19). Although the crown is smaller in all dimensions, its proportions usually correspond to those of the central incisor.
FIGURE 6-15 Maxillary right lateral incisor, mesial aspect. (Grid = 1 sq mm.)
FIGURE 6-16 Maxillary right lateral incisor, distal aspect. (Grid = 1 sq mm.)
FIGURE 6-17 Maxillary right lateral incisor, incisal aspect. (Grid = 1 sq mm.)
Figure 6-18 Maxillary lateral incisor, incisal aspect. Ten typical specimens are shown.
Figure 6-19 Maxillary lateral incisor, labial aspect. Ten typical specimens are shown.
Figure 6-20 Maxillary lateral incisor, mesial aspect. Ten typical specimens are shown.
The mesial outline of the crown from the labial aspect resembles that of the central incisor, with a more rounded mesioincisal angle. The crest of contour mesially is usually at the point of junction of the middle and incisal thirds; occasionally, in the so-called square forms, the mesioincisal angle is almost as sharp as that found on most maxillary central incisors (see Figure 6-19, 4 and 5). However, a more rounded mesioincisal angle is seen more often. The distal outline of the crown from the labial aspect differs somewhat from that of the central incisor.
The distal outline is always more rounded, and the crest of contour is more cervical, usually in the center of the middle third. Some forms describe a semicircular outline distally from the cervix to the center of the incisal ridge (see Figure 6-19, 3 and 7).
The labial surface of the crown is more convex than that of the central incisor except in some square and flat-faced forms.
This tooth is relatively narrow mesiodistally, usually about 2 mm narrower than the central incisor. The crown on the average measures from 2 to 3 mm shorter cervicoin-cisally than that of the central incisor, although the root is usually as long, if not somewhat longer, than that of the central incisor.
In general, its root length is greater in proportion to its crown length than that of the central incisor. The root is often about 1.5 times the length of the crown.
The root tapers evenly from the cervical line to a point approximately two thirds of its length apically. In most cases, it curves sharply from this location in a distal direction and ends in a pointed apex. Although the curvature distally is typical, some roots are straight (see Figure 6-19, 4, 7, and 9), and some may be found curving mesially. As mentioned previously, this tooth may show considerable variance in its crown form; the root form may be more characteristic.
Lingual Aspect
From the lingual aspect, mesial and distal marginal ridges are marked, and the cingulum is usually prominent, with a tendency toward deep developmental grooves within the lingual fossa, where it joins the cingulum (see Figure 6-14). The linguoincisal ridge is well developed, and the lingual fossa is more concave and circumscribed than that found on the central incisor. The tooth tapers toward the lingual,resembling a central incisor in this respect. It is not uncommon to find a deep developmental groove at the side of the cingulum, usually on the distal side, which may extend up on the root for part or all of its length. Faults in the enamel of the crown are often found in the deep portions of these developmental grooves (see Figure 6-21, 3 and 4).
FIGURE 6-21 Maxillary lateral incisor. Ten specimens with uncommon variations are shown. 1, Odd twist to crown and root. 2, Malformed generally. 3, Deep developmental (palatoradicular) groove distally; note pit in lingual fossa. 4, Same as specimen 3 with pit and groove connected. 5, Deep concavity above contact area of the crown. 6, Abnormally large but well formed. 7, Single-cusp development and malformed root called peg lateral incisor. 8, Same as specimen 7, except root is straight. 9, Same as specimen 5, with deep lingual pit in addition. 10, Resemblance to a small maxillary central incisor more marked than the average.
Table 6-2 Maxillary Lateral Incisor
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First evidence of calcification |
|
10-12 mo |
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Enamel completed |
4-5 yr |
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Eruption |
8-9 yr |
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Root completed |
11 yr |
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Measurement Table |
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Cervicoincisal Length of Crown |
Length of Root |
Mesiodistal Mesiodistal Diameter of Diameter Crown at of Crown Cervix |
Labio- or Buccolingual Diameter of Crown |
Labio- or Buccolingual Diameter of Crown at Cervix |
Curvature of Cervical Line—Mesial |
Curvature of Cervical Line—Distal |
|
Dimensions* suggested for carving technique |
9.0 |
13.0 |
6.5 5.0 |
6.0 |
5.0 |
3.0 |
2.0 |
Mesial Aspect
The mesial aspect of the maxillary lateral incisor is similar to that of a small central incisor except that the root appears longer (see Figures 6-15 and 6-20). The crown is shorter, the root is relatively longer, and the labiolingual measurement of the crown and root is a millimeter or so less than that of the maxillary central incisor of the same mouth.
The curvature of the cervical line is marked in the direction of the incisal ridge, although because of the small size of the crown the actual extent of curvature is less than that found on the central incisor. The heavy development of the incisal ridge accordingly makes the incisal portion appear somewhat thicker than that of the central incisor.
The root appears as a tapered cone from this aspect, with a bluntly rounded apical end. This varies in individuals, with the apical end sometimes being quite blunt, while at other times, it is pointed. In a good many cases, the labial outline of the root from this aspect is straight. As in the central incisor, a line drawn through the center of the root tends to bisect the incisal ridge of the crown.
Distal Aspect
Because of the placement of the crown on the root, the width of the crown distally appears thicker than it does on the mesial aspect from marginal ridge to labial face (see Figure 6-16). The curvature of the cervical line is usually a millimeter or so less in depth than on the mesial side. It is not uncommon to find a developmental groove distally on this crown extending on the root for part or all of its length.
Incisai Aspect
The incisal aspect of this tooth sometimes resembles that of the central incisor, or it may resemble that of a small canine (see Figures 6-17 and 6-18). If the tooth conforms in development to its central incisor neighbor in other respects, it will, from the incisal aspect, resemble a central incisor except in size (see Figure 6-18, 5 and 9). However, the cingulum may be large, as is the incisal ridge. In addition, the labio-lingual dimension may be greater than usual in comparison with the mesiodistal dimension. If these variations are present, the tooth has a marked resemblance to a small canine (see Figure 6-18, 3 and 10).
All maxillary lateral incisors exhibit more convexity labi-ally and lingually from the incisal aspect than do the maxillary central incisors.
