A. Introduction and comparison of terms:.
1. In the preceding unit, the cervical line, or cemento-enamel junction, was defined as the line around the tooth where the enamel and the cementum meet. It is a stable entity, in contrast to the gingival line, which may be ever changing.
2. The gingival line, also called the gingival margin or gingival crest, is the imaginary line which marks the level of termination of the nonattached soft tissue surrounding the tooth. The gingival line level is variable, and usually is above the cervical line early in life, often receding to a lower level as the individual becomes older. The gingival line separates the clinical crown and root, whereas the cervical line separates the anatomical crown and root. The gingival line is always observable clinically, while the cervical line is observable only when not covered by soft tissue, which is in a limited number of teeth.
3. The epithelial attachment is the actual attachment of the soft tissue of the mouth to the tooth. The epithelial attachment can be distinguished from the previously described periodontal ligament even though both structures are components of the tooth's attachment apparatus. The epithelial attachment serves as the connection for the soft (gingival) tissue and is limited in comparative area (but not importance), while the periodontal ligament provides the attachment of the hard tissue (bone) to the tooth's root structure, and is much more extensive in area. Since there is usually a sulcus between the gingival margin and the epithelial attachment, these two entities are not normally located at the same level on the tooth. However, like the gingival margin, the epithelial attachment may be variable in its location, and has a tendency to migrate apically during a person's lifetime, especially in the presence of periodontal disease. The epithelial attachment is normally found close to the level of the CEJ. However, as has been pointed out, the epithelial attachment has a tendency to move apically, so that it is possible for it to be located on the enamel of the cervical third of the crown in young persons, but on the cementum of the root in older individuals.
4. On any individual tooth, the amount (depth) of curvature of the cervical line seems to be related to the widths and lengths of the crown, as well as the location of the contact areas proximally.
B. Some general rules concerning cervical line contours in normal dentitions are as follows:
1. The cervical line is normally curved (convex) or bulges toward the apical on the facial and lingual surfaces of teeth.
2. The cervical line is normally curved (convex) toward the incisai (occlusal) on the mesial and distal surfaces of teeth.
DIRECTION OF CURVATURE
3. The amount (depth) of cervical line curvature on any individual tooth is normally greater on the mesial, as compared to the distal surface.
DEPTH OF CURVATURE
4. Cervical lines on adjacent proximal surfaces of adjacent teeth have approximately the same depth of curvature.
5. The depth of the curvature on all surfaces is greatest on central incisors, and decreases posteriorly.
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