Exposure of root surfaces
In the young, healthy adult, root surfaces, like the cementoenamel junctions, are not exposed to the oral cavity. At the population level, the prevalence of exposed root surfaces is strictly age related and is attributed to the long-term effects of trauma from toothbrushing (buccal surfaces) and gingival recession associated with periodontal disease. With the decline in prevalence and severity of enamel caries, and hence the preservation of an intact dentition into old age, root caries is becoming an increasing problem in clinical practice. A discussion of tooth resistance must therefore include possible predictors of the development of root caries in the individual tooth.
Morphologically, the surface of intact cementum and the cementoenamel junction are very rough, compared to the enamel surface (Fig 122). Because the rough surface is highly retentive to plaque¾both supragingival and subgingival (Fig 123)so-called root planing is emphasized as an important phase of scaling procedures in periodontal therapy. The roughness of the intact root cementum may vary from individual to individual as well as between different tooth surfaces.
The prevalence of cementum hypoplasia may also differ, not only between populations and individuals, but also symmetrically between different teeth. For example, subjects with localized early-onset periodontitis have a high prevalence (Lindskog and Blomlof, 1983) of cementum hypoplasia in first molars and central incisors (Fig 124). Such disturbances of cementum formation should be symmetric, because the cementum of all first molars and central incisors forms during the same period. It may be speculated that excessive doses of, for example, fluoride result not
only in enamel hypoplasia (fluorosis) but also in cementum hypoplasia.
If root dentin is exposed by cementum hypoplasia or by aggressive removal of root cementum by scaling, bacteria may migrate via the dentinal tubules into the pulp (Adriaens et al, 1986, 1988a, b). Other studies have shown that if the root cementum is absent, bacteria from infected root canals may migrate to the root surface, initiating or maintaining local periodontitis (Jansson et al, 1995; Ehnevid et al, 1995a).
It should also be noted that root cementum and dentin are quite different from enamel in chemical composition: organic components constitute less than 1% of enamel but 35% to 40% of the total volume of root cementum and dentin. Not only the etiology but also the histopathology of root caries is therefore different from enamel caries: A synergistic effect of acidogenic bacteria and bacteria that produce proteolytic enzymes (mainly collagenases) has been proposed.
