Protecting Against Root Caries

The dental caries process begins with the loss of calcium ions from the
surface apatite crystals that form the bulk of the three calcified dental
tissues. Under normal circumstances, this loss of calcium (demineralization)
is compensated by the uptake of calcium (remineralization) from the tooth’s
microenvironment. This dynamic process of demineralization and
remineralization takes place more or less continually and equally in a
favourable oral environment. In an unfavourable environment, the
remineralization rate does not sufficiently neutralize the rate of
demineralization and caries occurs.
The natural history of dental caries can be viewed as a continuum, a series
of stages, from microscopic demineralization of apatite to an active,
cavitated, progressively enlarging lesion (Dodds & Wefel, 1995) 
The latter part of this continuum has been divided arbitrarily into stages and
assigned labels such as early, white spot, incipient and advanced that assist
us when making decisions regarding clinical management. Diagnosis of caries
involves primarily visual-tactile methods but radiographs are also extensively
used.
There is a general consensus among clinicians that for coronal caries,
restorative treatment is indicated if the lesion is cavitated and extends into3
the dentine (Community Dental Health Research Unit, 1995). There is nno such
consensus regarding root caries. Root caries can involve the cementum first
but, in most situations, it begins in the dentine (Figure 2). There is no whitespot lesion associated with root caries and the clinical stages of the disorder
have been arbitrarily divided into stages based on the texture and the depth
of the surface defect (Billings et al, 1985; Billings 1986).
Clinical studies have convincingly demonstrated that the caries process,
whether it involves the crown (enamel) or the root (cementum, dentine) of
the tooth can be reversed or, at least, arrested, even if the tooth surface is
cavitated. Reversing the caries process (remineralization) is probably
dependent more on the microenvironment surrounding the tooth or adjacent
to a particular tooth surface than on the size or extent of the existing
lesion. However, while the caries process can be interrupted at virtually any
point, any loss of structure cannot be replaced. For coronal caries involving
the enamel, loss of structure implies loss of mineral. For coronal caries
involving the dentine and for root caries, there is both loss of mineral and
loss of protein (proteolysis). Remineralization involving the dentine has been
shown to take place on the remaining mineral content rather than on the
protein infrastructure (Wefel et al, 1985).
It is not known exactly how long it takes for a coronal caries lesion to
develop because our diagnostic tools are not yet sensitive enough to pick up
sub-clinical lesions or the very early clinical stages of the disease. However,
once a carious lesion is diagnosed clinically, it is possible to trace its
development or progression. In general, caries progression within the enamel
of permanent teeth is a slow process, requiring an average of three or four
years to reach dentine (Community Dental Health Services Research Unit,
1993). Within dentine, caries progression is not as well documented as most
caries that reaches the dentine is treated with a restoration before it
progresses deeply into the dentine. The progression of root caries, being
essentially dentinal caries, is also largely undocumented.
It will be possible, with the use of emerging technology, to shift the
diagnostic decision regarding the presence of decalcification (dental caries)
further to the left- to the area of very early lesion development or, inn fact,
to a point beyond our ability to visualize the disease in the mouth. This ability
to diagnose dental caries earlier in its natural history at a point even before
we can visualize it clinically has several attractions. It would allow clinicians
to manage the caries process at an earlier stage and initiate preventive
rather than treatment measures. And, it will obviate the need to surgically4
correct the disorder thereby introducing cost savings, assuming that
medical treatment is less costly than surgical treatment.
Since this Consensus Conference has been charged with the task of
determining the “best methods for detecting early-stage and late-stage
dental caries”, this presentation will discuss the clinical diagnosis of root
caries by examining the validity and reliability of traditional visual-tactile
methods and the use of existing diagnostic tests to supplement visual-tactile
assessments.
Epidemiology of Root Caries
There is little disagreement in the literature regarding the distribution of
root caries lesions. Root caries, by definition, occurs on the root of the
tooth. Some investigators have made a distinction between root caries that
originates wholly on the root surface and caries that spreads from the
coronal surface onto the root surface. Lynch (1994) refers to caries that
begins on the root surface as “primary root caries”. The term “primary” as
it is used with root caries refers to new dental caries occurring in the
absence of a restoration. Secondary (recurrent) root caries refers to caries
occurring adjacent to an existing restoration. There is already general
agreement on this terminology.
Clinical researchers agree that root caries can occur anywhere on the root
surface. But, there are conflicting views about root lesions in the area of the
cemento-enamel junction (CEJ) as to whether the initial caries occurred on
the crown or the root of the tooth. With location, the issue is whether or not
to classify caries in the area of the CEJ as root caries extending onto the
crown, as coronal caries extending onto the root or both. This, however, is a
measurement issue more than a diagnostic issue.
Root caries occurs supragingivally, most often at or close to (i.e. within
2mm) the cemento-enamel junction. This phenomenon has been attributed to
the location of the gingival margin at the time conditions were favorable for
caries to occur (Banting, 1976; Banting et al, 1985; Lynch and Beighton,
1994). The location of root caries has been positively associated with age
and gingival recession and this is consistent with the concept that root
caries occurs in a location adjacent to the crest of the gingiva where dental
plaque accumulates. Root caries occurs predominently on the proximal5
(mesial and distal) surfaces, followed by the facial surface (Banting et al,
1985; Schaeken et al, 1991, Fure, 1997; Banting et al, 2001).
Early root caries tends to be diffuse (spread out) and track along the
cemento-enamel junction or the root surface. More advanced root lesions
begin to progress toward the pulp much like dentinal caries in the tooth
crown.
Several reviews of root caries have been published in the past decade (Beck,
1990; Hellyer and Lynch, 1991; Titus, 1992; Billings and Banting, 1993;
Ravald, 1994) and readers are directed to them for further information.
Similarities and Differences between Coronal and Root Caries that
Influence Diagnosis and Management
There are many similarities and a few differences between coronal and root
caries that necessitate different approaches to and criteria for clinical
diagnosis (Table 1).
Coronal and root caries share common risk factors (mutans Streptococci,
Lactobacilli), common predisposing factors and appear to share a similar
process of dentine destruction and remineralization (Wefel et al, 1985;
Frank, 1990; Schupbach et al, 1989,1990; Zambon and Kasprzak, 1995).
There are, however, subtle differences related to the pH at which
demineralization begins, the role of proteolytic enzymes in the destruction of
the initial target tissue and the rate of lesion progression.
Some investigators, nevertheless, consider coronal and root caries to be
similar disorders (Billings and Banting, 1993).
The diagnostic criteria for coronal and root caries differ primarily because
of the composition of the tissues forming the outer layer of the crown and
root respectively (Scott and Symons, 1974; Provenza, 1988). Coronal caries
almost always begins in highly mineralized enamel. Root caries, however may
involve the less mineralized cementum first or, more likely, the dentine which
is also contains much less mineral than enamel. The cemento-enamel junction
can have cementum overlapping enamel (60-65%), cementum abutting
enamel (25-30%) or a space between the cementum and the enamel where
dentine is exposed (10%) and even all three situations on the same tooth
(Scott and Symons, 1974; Provenza, 1988). Because of the thinness of the
cementum in this region of the root, and the extent to which scaling and root6
planing procedures are routinely applied in developed countries, there is a
high probability that the cementum has been removed in the area of the
cemento-enamel junction and the coronal third of the root. Therefore, root
caries is, for all intents and purposes, dentinal caries.
Clinical Signs of Root Caries
Clinical diagnosis is the process of recognizing diseases by their
characteristic signs and symptoms. It is an imperfect process because there
is considerable variation both in the signs and symptoms of disease in
individual subjects and in the interpretation of those signs and symptoms by
clinicians. Nevertheless, clinical observations are extensively relied upon for
diagnosis in the absence of more definitive methods.
The clinical investigators who first studied root caries provided clinical
descriptions of the signs and symptoms of root caries lesions (Hazen et al.,
1973; Sumney et al., 1973; Hix and O’Leary, 1976; Banting et al., 1980; Katz
et al., 1982; Vehkalahti et al., 1983; Beck et al., 1985; NIDR, 1987). The
most commonly used clinical signs to describe root caries utilized visual
(color, contour, surface cavitation) and tactile (surface texture)
specifications (Banting, 1993). There are no reported clinical symptoms of
root caries although pain may be present in advanced lesions. (Table 2).
There are intriguing contrasts in the description of the contour, cavitation
and color aspects of a root caries lesion. Sumney et al. (1973) found root
caries lesions to be "shallow and ill-defined". Hix and O’Leary (1976) describe
root caries lesions as "well-established". Banting et al. (1980), in direct
contrast to Sumney et al. (1973), consider root caries lesions to be
"discrete” and “well-defined" lesions. Several investigators describe the root
caries lesion as "discolored" or "darker" while others indicate that there is a
specific color change to "yellow/orange", "tan" or "light brown" associated
with the root caries process. Although no correlation has been demonstrated
between the color of root lesions and caries activity (Hellyer et al, 1990;
Shaeken et al, 1991, Lynch and Beighton, 1994), it is unanimously agreed
that discoloration of the root surface is indicative of the presence of caries.
Although root caries is referred to as a "lesion", it is not at all clear whether
a cavity (or loss of surface continuity) must necessarily be present in the
early stages of the disease. Whether a probe needs to be used to confirm
loss of surface continuity has generated considerable debate for coronal7
caries diagnosis and the arguments would likely apply equally well for root
caries diagnosis. Nevertheless, clinical investigators are in agreement about
active root caries being "soft" when gently probed with an explorer.
The presence of cavitation is often difficult to determine visually and thus
probes are used to detect surface defects. On enamel, it is possible to run
the probe across the surface and detect a roughness that is indicative of
cavitation. On cementum or dentine, however, this is not as easy to do. The
lower degree of mineralization of cementum and dentine does not permit the
probe tip to glide freely over the surface when the surface is intact.
Tactile diagnosis of caries has used probe “tug back” as a sign of the
presence of caries. This has served the clinician well in coronal caries where
the caries extends into the dentine. Dentine caries is soft, relative to the
enamel and the presence of this softness, as evidenced by a “tug back” on
the probe has been used to indicate dentinal caries. However, non-carious
dentine and cementum are “soft” calcified tissues and can produce some
“tug back’ on the probe in the absence of caries. Assuming that the probing
pressure used is the same, the presence of “tug back” on the root surface
is, therefore, more likely to result in a false positive diagnosis of dental
caries. Nevertheless, texture, is used extensively used by clinicians to aid in
the determination of root caries.
The traditional methods of visual-tactile diagnosis for root caries can
produce a correct diagnosis but usually not until the lesion is at an advanced
stage. Because of the fundamental differences in coronal and root caries,
coronal caries is more likely to be confidently diagnosed at an earlier stage
than root caries using visual-tactile methods. Setting aside the argument
that probing can hasten the development of caries, the disadvantage of
diagnosing root caries using visual-tactile methods is that a larger or more
advanced surface defect needs to be present before a positive diagnosis can
be made.
Clinical investigators have advocated expanded categories for visual-tactile
root caries diagnosis (Fejerskov et al, 1991) (Table 3). These provide the
clinician with additional information regarding the root lesion that can be
helpful for describing the physical characteristics of the lesion. Although
these expanded criteria are useful for research purposes, their usefulness
to the clinician is limited for determining whether or not root caries may be
present. These expanded criteria, however, have been used to classify root
lesions according to their activity (Table 4). Unfortunately, color has not8
been found to be well correlated with root caries activity and probing
pressure can be highly variable.
Combinations of signs have been related to potential treatment protocols for
root caries (Beighton et al, 1993; Lynch and Beighton, 1994) (Table 5). This
can provide a guideline for clinicians regarding the most appropriate
treatment to provide for a given root lesion.
Although more categories of signs and symptoms can provide more
information and, therefore, for more precision in the diagnostic process,
they also generate more variability in the diagnosis.