Root caries

29-03-2010
Root caries
According to Hix and O’Leary (1976), root surface caries is defined as “a cavitation
or softened area in the root surface which might or might not involve adjacent enamel
or existing restorations (primary and recurrent lesions).” Nyvad and Fejerskov (1987)
introduced the definitions of active and inactive carious lesions of the root. Root
caries may be classified as primary or secondary, cementum or dentin, active or
inactive, and with or without cavitation (see Table 15). The lesions can also be
classified according to the texture (soft, leathery, or hard) and the color (yellow, light
brown, dark brown, or black).
Development
The initial conditions necessary for development of carious lesions at the root are:
1. A root surface accessible to a cariogenic microflora
2. Exposure of the root surface to cariogenic plaque (biomass) until the lesions
develop
Root surfaces inevitably are exposed by gingival recession resulting from poor oral
hygiene and gradual loss of periodontal attachment with age. Even in populations
with adequate oral hygiene, some recession occurs, with a highly characteristic
pattern of distribution in elderly populations. Another typical pattern is frequently
seen on the buccal surfaces of several teeth in adolescents, attributed to inappropriate
plaque control procedures, ie, iatrogenic effects of horizontal toothbrushing.
When root surfaces are exposed to the oral environment as a result of gingival
recession, there is an increase in areas of potential plaque retention, particularly in the
large interproximal areas and along the gingival margin and the cementoenamel
junctions, which represent stagnant areas for accumulation of plaque (Figs 182 and
183). In addition, compared to the enamel surface, the intact root surface is very
rough and retentive to plaque. Therefore, the primary carious lesion of the root has a
greater horizontal than vertical dimension, because of greater plaque buildup along
the gingival margin.
Initial active root lesions are soft on probing, have a leathery consistency, and are
normally covered with plaque. The color is yellow or light brown. However, Lynch
and Beighton (1994) reported that, irrespective of the color, soft active lesions are
closest to the gingival margin and hard inactive lesions are the most distant; leathery
lesions occupy an intermediate position.
Experimental studies have shown that carious lesions develop very rapidly on root
surfaces continuously covered with plaque (Nyvad et al, 1989). Figure 184 shows a
microradiogram, illustrating the depth and shape of the root carious lesion after 1, 2,
and 3 months. There is a gradual increase in mineral content in the surface zone,
despite progressive loss of subsurface mineral.
The surface of the radicular carious lesion is infiltrated by microorganisms at a very
early stage. The bacteria seem to split the collagen fibers of the cementodentinal
junction, and microorganisms may be found in the many exposed dentinal tubules
even in initial root lesions. The response by the dentin is similar to that described for
coronal caries; ie, the pulpodentinal organ corresponding to the involved areas of the
root responds with increased mineralization deep within the tissue, resulting in a zone
of higher mineral content in the involved areas. Likewise, tertiary, reactive dentin is
frequently observed at the pulpal surface of the dentin, corresponding to the involved
tubules.
If the exposed root surface is still covered by a layer of cementum, the early stages in
caries development normally involve a haphazard demineralization of this layer (Fig
185), because of acid formed by the acidogenic bacteria colonizing the root surface.
Because of the much higher organic content in the hard tissue of the root, species
other than those initiating enamel caries may sometimes be involved in the
development of root lesions.
For example, in teeth with periodontitis, scaling and root planing may in places
completely remove the hypermineralized cementum. In such areas, the combination of
acidogenic and proteolytic bacteria will result in wide root dentin lesions beneath the
remaining root cementum (Fig 186). The root cementum is only 0.03 to 0.10 mm
thick on the coronal third of the root: 10 to 20 strokes with a sharp curette or a 0.10-
second application of a 15-um diamond-coated rotating tip can completely remove
such a thin layer, exposing the dentinal tubules of the root, which will immediately be
invaded by microorganisms. A nonaggressive approach to scaling and debridement is
therefore important.
Although root lesions do not usually exhibit cavities, it is very important that the
surface zone of active radicular carious lesions not be iatrogenically damaged by
gentle probing or by scaling. As with the surface zone of active carious lesions in
enamel, damage to the surface of a root lesion may initiate the development of
localized cavities.
Arrest
Despite the invasion of microorganisms into dentinal tubules in most carious lesions
of the root, it is possible to arrest active lesions through improvement in oral hygiene
and use of fluoride toothpaste. Studies by Nyvad and Fejerskov (1986) in elderly
patients with active root lesions showed that improved oral hygiene converted active
lesions to inactive lesions. Figure 187 illustrates how, with improved oral hygiene, an
active, plaque-covered root lesion on the buccal surface of a maxillary left canine
gradually underwent changes in color and surface structure as the lesion became
inactive. In a more recent study by Nyvad et al (1997), carious lesions were
experimentally developed in situ on root specimens borne in partial dentures and then
arrested by cleaning with fluoride toothpaste for 3 months.
Even root lesions with deep cavities can successfully be converted to inactive lesions
by improved plaque control and use of fluoride. Figure 188 by Nyvad and Fejerskov
(1997) shows active, plaque-covered root caries with a typical yellow color and a soft
surface. After improved plaque control and topical use of fluoride, 10 years later the
cavities were inactive, with a typical dark brown to black color and a semihard
surface

 

 
 
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Dentin caries
29-03-2010
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