OBJECTIVES

Unlike incisors where there are two types (a central and a lateral), there is only one type of canine. Therefore, type traits do not apply to canines, but arch traits are useful to distinguish maxillary from mandibular canines.

Have Appendix pages 3 and 4 available, and ideally have several extracted canines or models to study, and refer to Figure 3-8 as you read this section. Hold maxillary canines with crowns down and mandibular canines with crowns up. This is the way they are oriented in the mouth.

A. CANINES FROM THE LABIAL VIEW

1. Canine Morphology (Labial View)

The facial side of any canine crown is formed from three labial lobes like the incisors. (The cingulum on the lingual side of the crown forms from the fourth lobe.) The middle lobe on the facial forms the labial ridge (Appendix 3c), which can be quite prominent on the maxillary canine. The labial ridge runs cervicoincisally near the center of the crown in the middle and incisal thirds. Shallow depressions may be evident mesial and distal to the labial ridge (recall Fig. 3-6). See Table 3-1 for a summary of the number of lobes that form canines.

TABLE 3-1

Guideline for Determining the Number of Lobes for Canines

Rule: Number of lobes = 3 facial lobes + 1 lingual lobe for the cingulum, the same as for incisors.

The labial surface of a mandibular canine is more smooth and convex. A labial ridge may be present but not as pronounced as on the maxillary canines. In the incisal third, the labial crown surface is convex but slightly flattened mesial to the labial ridge and even a little more flattened distal to the ridge (best seen from the incisal view, but can be felt on the labial surface).

2. Canine Shape and Size (Labial View)

When viewed from the labial, the mesial outline of the maxillary canine crown is broadly convex in the middle third, becoming nearly flat in the cervical third (Appendix 4b). The outline of the distal portion of the maxillary canine crown may have a shallow S shape, being convex in the middle third (over the height of contour or proximal contact area) and slightly concave in the cervical third (Fig. 3-7).

The mandibular canine crown appears longer and narrower than does the crown of the maxillary canine^D (Appendix 4a). When viewed from the facial, the mesial outline of the mandibular crown is almost flat to slightly convex, nearly in line with the mesial outline of the root, and may not bulge or project beyond the mesial root outline (Appendix 4b and Fig. 3-9A and B). This conspicuous feature is also quite evident in most mandibular canines in Figure 3-8 but is not seen on maxillary canines. The distal side of the crown may be slightly concave in the cervical third (Fig. 3-9B); it is convex in the incisal two thirds. There is noticeably more of the crown distal to the root axis line than mesial to it. This often makes the lower canine crown appear to be tilted or bent distally when the root is held in a vertical position (similar to the mandibular lateral incisor just mesial to it).

3. Canine Cusp Tip and Incisal Ridges (Labial View)

Recall that the mesial cusp ridges are normally shorter than the distal ridges for all canines. The cusp and cusp ridges of the maxillary canine make up nearly one third of the cervicoincisal length of the crown, because the angle formed by the cusp ridges is relatively sharp, slightly more than a right angle (105 degrees) (Appendix 4c). Compare this to the cusp tip of the mandibular canine, where cusp ridges form a less sharp, more obtuse (blunt) angle (120 degrees) (Appendix 4c). Sharper maxillary canine cusps and less sharp mandibular cusps are evident in almost all canines in Figure 3-8. The mesial cusp ridge of the mandibular canine is also almost horizontal compared to its longer distal cusp ridge, which slopes more steeply in an apical direction. Shorter, more horizontal mesial cusp ridges are seen clearly in Figure 3-9A and B and on most mandibular canines in Figure 3-8.

4. Canine Proximal Contact Areas (Labial View)

The mesial contact area of the maxillary canine is located at the junction of the incisal and middle thirds. The distal contact area of the maxillary canine, like all anterior teeth, is in a more cervical location on the distal side than on the mesial side. It is located in the middle third, often just cervical to the junction of the incisal and middle thirds (recall Appendix 3g and Fig. 3-7). This is the only canine proximal contact area (mesial or distal) located in the middle third, and it is the most cervical contact of all anterior teeth.

The mesial contact area of the mandibular canine is in a more incisal position than on the maxillary canine due to the more incisal, nearly horizontal mesial cusp ridge on the mandibular canine. It is in the incisal third just cervical to the mesioincisal angle. The distal contact area is, as expected, more cervical than is the mesial, at the junction of the middle and incisal thirds (Fig. 3-9B). See Table 3-2 for a summary of the location of contact areas on canines.

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