Diagnosis of secondary caries
Definition and prevalence
Secondary caries has been reported to be eight times more common than primary lesions in adults, particularly in those older than 50 years (Goldberg et al, 1981).
However, prevalence may vary markedly in different countries, depending on the total caries prevalence in the population and the level of development of the dental care system. In developing countries with low caries prevalence in the adult population and poor dental care resources, secondary caries may be almost negligible. On the other hand, the prevalence of secondary caries is very high in industrialized countries with high caries prevalence among adults (particularly many filled surfaces) and a dental care system with emphasis on restorative rather than preventive dentistry.
In a cross-sectional study in randomized samples of 35, 50, 65, and 75 year olds in the county of Varmland, Sweden, examined by a combination of meticulous clinical visual examination and complete-mouth radiographs, 1.0 secondary lesion per individual was found, on average, in the 50, 65, and 75 year olds. The number of primary coronal lesions was 0.4, 0.3, and 0.2, respectively, in the three older age groups. The number of root lesions was 0.3 in 50, 65, and 75 year olds. The 35 year olds exhibited 0.7 secondary lesions and 0.7 primary coronal lesions, but no root
lesions (Axelsson et al, 1990). In a 15-year longitudinal preventive study based on mechanical plaque control, the subjects developed only one new carious lesion per individual per 15 years, even though the oldest age group was 65 to 85 years old at reexamination. However, 90% of the lesions were secondary caries (Axelsson et al, 1991).
With the exception of the occlusal surfaces, secondary caries occurs most frequently on the surfaces most frequently restored, ie, the approximal surfaces of the posterior teeth (mostly subgingivally), followed by the buccal surfaces of the posterior teeth and the lingual surfaces of the mandibular molars. According to a recent review, secondary caries is the major reason for the failure of restorations (Kidd et al, 1992).
Diagnostic methods
The diagnosis of secondary caries is usually based on clinical examination, including gentle probing, and may not be correct. For example, it is generally considered that the wider the gap at defective margins of restorations, the greater the likelihood of recurrent caries. Two studies in which extracted teeth were examined visually and by probing revealed these methods to have poor validity, predictive value, and specificity for detection of actual secondary caries, as determined after the removal of the restoration (Soderholm et al, 1989) or sectioning of the tooth. In fact, in more than 50% of cases in which replacement of the filling was recommended, this was not justified on the basis of true secondary caries.
There are, however, other indications for replacing restorations with faulty margins.
In a study attempting long-term elimination of mutans streptococci from the mouths of adults by use of chlorhexidine varnish, treatment was unsuccessful in one third of the subjects, because of retentive areas that served as a reservoir for the organisms (Sandham et al, 1988).
The difficulties involved in diagnosis of secondary caries are only in some respects similar to those in primary lesions. As with primary lesions, there is the problem of differentiating active caries from a chronic, static lesion. If a lesion is not progressing, it may not require operative intervention. Unfortunately there are currently no clinical variables with which to differentiate active from inactive secondary caries. Secondary caries may be located on the crown as well as on the root and is frequently located cervically, involving both crown and root along the cementoenamel junction. It may be noncavitated or cavitated (see Table 15).
The diagnosis of secondary caries is also associated with other problems. First, lesions
on the occlusal surface, between the restoration and the enamel (the so-called wall
lesion) cannot be detected until they have reached an advanced stage. Such lesions
spread more in the dentin than in the enamel. The color next to amalgam is not always
predictive, because gray or blue discoloration could be due to corrosion products as
well as to secondary caries.
Second, lesions at the cervical approximal margin, the most frequent site of secondary
lesions (about 94% of amalgam and 62% of composite restorations) (Mjor, 1985), can
be detected only on radiographs, by careful comparison with previous bitewing
radiographs. Dark shadows at the margin of the restoration indicate secondary caries
(Fig 228). However, the lesion may not always be detectable on the radiograph: For
example, a limited secondary lesion on the mesiolingual margin of a restoration may
be obscured by a more apically located mesiobuccal margin. Radiographs should,
therefore, be used in combination with meticulous clinical examination, including
probing, to determine whether the lesion is cavitated or not. Accessibility for probing
the cervical margins of approximal restorations is not a problem.
Figure 229 shows, in chronologic order, a Norwegian five-grade system for scoring
secondary caries on the approximal surfaces (Espelid and Tveit, 1986):
· Grade 1: noncavitated white spot or light, discolored lesion and/or radiographically
detectable lesion in the outer half of the enamel
· Grade 2: superficial cavitation and/or radiographic lesion in the inner half of the
enamel
· Grade 3: small cavity and/or radiographic lesion in the outer third of the dentin
· Grade 4: substantial cavity and/or radiographic lesion into the middle third of the
dentin
· Grade 5: advanced cavitation and/or radiographic lesion into the inner third of the
dentin
