Detailed Description of Each Primary Tooth
MAXILLARY CENTRAL INCISOR
Labial Aspect
In the crown of the primary central incisor, the mesiodistal diameter is greater than the cervicoincisal length (Figures 3-10 and 3-11, A). (The opposite is true of permanent central incisors.)
Figure 3-8 Permanent central incisor. A, Pulp canal; B, pulp horns. This figure represents a sectioned central incisor of a young person. Although the pulp canal is rather large, it is smaller than the pulp canal shown in Figure 3-9, and it becomes more constricted apically. Note the dentin space between the pulp horns and the incisal edge of the crown.
Figure 3-9 Primary central incisor. A, Pulp canal; B, pulp horns. This figure represents a sectioned primary central incisor. The pulp chamber with its horns and the pulp canal are broader than those found in Figure 3-8. The apical portion of the canal is much less constricted than that of the permanent tooth. Note the narrow dentin space incisally.
Figure 3-10 Primary maxillary central incisors (first incisors). 1, Labial aspect. Note the lack of character in the mold form; also note the mesiodistal width compared with the shorter crown length. A little of the crown length was lost through abrasion before the date of extraction. 2, Mesial aspect. The cervical ridges are quite prominent labially and lingually, with the bulge much greater than that found on permanent incisors. This characteristic is common to each primary tooth to a varied degree. Normally, these curvatures are covered by gingival tissue with epithelial attachment. 3, Incisal aspect.
The labial surface is very smooth, and the incisal edge is nearly straight. Developmental lines are usually not seen. The root is cone-shaped with even, tapered sides. The root length is greater in comparison with the crown length than that of the permanent central incisor. It is advisable when studying both the primary and permanent teeth to make direct comparisons between the table of measurements of the primary teeth (Table 3-1) and that of permanent teeth (see Table 1-1).
Lingual Aspect
The lingual aspect of the crown shows well-developed marginal ridges and a highly developed cingulum (Figure 3-12, A). The cingulum extends up toward the incisal ridge far enough to make a partial division of the concavity on the lingual surface below the incisal edge, practically dividing it into a mesial and distal fossa.
The root narrows lingually and presents a ridge for its full length in comparison with a flatter surface labially. A cross section through the root where it joins the crown shows an outline that is somewhat triangular in shape, with the labial surface making one side of the triangle and mesial and distal surfaces making up the other two sides.
Mesial and Distal Aspects
The mesial and distal aspects of the primary maxillary central incisors are similar (Figure 3-13, A; see also Figure 3-10). The measurement of the crown at the cervical third shows the crown from this aspect to be wide in relation to its total length. The average measurement is only about 1 mm less than the entire crown length cervicoincisally. Because of the short crown and its labiolingual measurement, the crown appears thick at the middle third and even down toward the incisal third. The curvature of the cervical line, which represents the cementoenamel junction (CEJ), is distinct, curving toward the incisal ridge. However, the curvature is not as great as that found on its permanent successor. The cervical curvature distally is less than the curvature mesially, a design that compares favorably with the permanent central incisor.
Figure 3-11 Primary right anterior teeth, labial aspect. A, Maxillary central incisor. B, Maxillary lateral incisor. C, Maxillary canine. D, Mandibular central incisor. E, Mandibular lateral incisor. F, Mandibular canine.
Figure 3-12 Primary right anterior teeth, lingual aspect. A, Maxillary central incisor. B, Maxillary lateral incisor. C, Maxillary canine. D, Mandibular central incisor. E, Mandibular lateral incisor. F, Mandibular canine.
Table 3-1 Table of Measurements of the Primary Teeth of Man (Averages Only) (in Millimeters)
Length Overall |
Length of Crown |
Length of Root |
Mesiodistal Diameter of Crown |
Mesiodistal Diameter of Crown at Cervix |
Labiolingual Diameter of Crown |
Labiolingual Diameter of Crown at Cervix |
|
Upper Teeth |
|||||||
Central incisor |
16.0 |
6.0 |
10.0 |
6.5 |
4.5 |
5.0 |
4.0 |
Lateral incisor |
15.8 |
5.6 |
11.4 |
5.1 |
3.7 |
4.0 |
3.7 |
Canine |
19.0 |
6.5 |
13.5 |
7.0 |
5.1 |
7.0 |
5.5 |
First molar |
15.2 |
5.1 |
10.0 |
7.3 |
5.2 |
8.5 |
6.9 |
Second molar |
17.5 |
5.7 |
11.7 |
8.2 |
6.4 |
10.0 |
8.3 |
Lower Teeth |
|||||||
Central incisor |
14.0 |
5.0 |
9.0 |
4.2 |
3.0 |
4.0 |
3.5 |
Lateral incisor |
15.0 |
5.2 |
10.0 |
4.1 |
3.0 |
4.0 |
3.5 |
Canine |
17.5 |
6.0 |
11.5 |
5.0 |
3.7 |
4.8 |
4.0 |
First molar |
15.8 |
6.0 |
9.8 |
7.7 |
6.5 |
7.0 |
5.3 |
Second molar |
18.8 |
5.5 |
11.3 |
9.9 |
7.2 |
8.7 |
6.4 |
Figure 3-13 Primary right anterior teeth, mesial aspect. A, Maxillary central incisor. B, Maxillary lateral incisor. C, Maxillary canine. D, Mandibular central incisor. E, Mandibular lateral incisor. F, Mandibular canine.
Although the root appears more blunt from this aspect than it did from the labial and lingual aspects, it is still of an even taper and the shape of a long cone. However, it is blunt at the apex. Usually the mesial surface of the root will have a developmental groove or concavity, whereas distally, the surface is generally convex.
Note the development of the cervical ridges of enamel at the cervical third of the crown labially and lingually.
Incisal Aspect
An important feature to note from the incisal aspect is the measurement mesiodistally compared with the measurement labiolingually (Figure 3-14, A; see also Figure 3-10, 3). The incisal edge is centered over the main bulk of the crown and is relatively straight. Looking down on the incisal edge, the labial surface is much broader and also smoother than the lingual surface. The lingual surface tapers toward the cingulum.
The mesial and the distal surfaces of this tooth are relatively broad. The mesial and distal surfaces toward the incisal ridge or at the incisal third are generous enough to make good contact areas with the adjoining teeth, although this facility is used for a short period only because of rapid changes that take place in the jaws of children.
Maxillary lateral Incisor
In general, the maxillary lateral is similar to the central incisor from all aspects, but its dimensions differ (Figure 3-15; see also Figures 3-11, B; 3-12, B; 3-13, B; and 3-14, B). Its crown is smaller in all directions. The cervicoincisal length of the lateral crown is greater than its mesiodistal width. The distoincisal angles of the crown are more rounded than those of the central incisor. Although the root has a similar shape, it is much longer in proportion to its crown than the central ratio indicates when a comparison is made.
Figure 3-14 Primary right anterior teeth, incisal aspect. A, Maxillary central incisor. B, Maxillary lateral incisor. C, Maxillary canine. D, Mandibular central incisor. E, Mandibular lateral incisor. F, Mandibular canine.