July 1st, 2009 by admin

Secondary or recurrent caries is
primary caries at the margin of a
restoration
. The clinical diagnostic criteria are thus identical to those for
primar y caries as described above
Ditched
amalgam restorations.
Clinical-visual examination
A particular problem, with amalgam restorations is marginal breakdown or
fracture, often called
ditching
(Figure 3.15). This has long been regarded
with suspicion by clinicians, and restorations replaced as a preventive meas-
ure to avoid plaque stagnation in this area. There are a number of reasons
why this approach is incorrect:
• Ditching occurs occlusally in an area that is easy to clean. Recurrent
caries usually occurs approximally and cervically in areas of plaque
stagnation.
• Clinical study has shown ditching does not reliably predict infected
dentine beneath the ditched area unless the ditch is an obvious cavity that
would admit the tip of a periodontal probe (over 0.4 mm).
• When dentists remove ditched fillings, they overcut cavities by as much as
0.6 mm. The dentist may also perpetuate the error of cavity preparation
and restoration which caused the ditching problem. This is often too sharp
an amalgam–margin angle, which makes the edge of the filling prone to
fracture. The tooth is thus in danger of entering a repetitive restorative
cycle until the dentist literally runs out of tooth tissue.
Discoloration
around restorations with clinically intact margins also
does not reliably predict new caries beneath the restoration (Figure 3.16).
Sometimes discoloration around an amalgam can be caused by corrosion
products from the amalgam or by light re ecting from the amalgam itself
through the relatively translucent enamel. Discoloration around amalgam
may also indicate demineralized, stained dentine, but this is residual caries
left by the dentist who placed the filling. If these restorations are removed, the
dentine is discoloured but either hard or crumbly and dry and not heavily
infected. This does not indicate new disease. Staining around an amalgam
restoration should not trigger its replacement unless a carious cavity, or a
very wide ditch that traps plaque, is also present (Figure 3.17).
Colour changes around tooth-coloured filling materials may come in a
number of forms. An active white spot lesion may be present and preventive
treatment is indicated. A line of stain at the junction of the filling and the
 CARIES DIAGNOSIS
tooth may indicate leakage around the filling, but unless the patient requests
its replacement because of poor appearance, operative treatment is not
required (Figure 3.18).
Stain around a tooth-coloured filling can also present as grey or brown dis-
coloured dentine shining up through intact enamel (Figure 3.19). This appear-
ance probably represents residual caries left when the cavity was originally
repaired. Clinical study indicates that this appearance does not reliably indicate
CARIES DIAGNOSIS
infected dentine (and presumably active demineralization) beneath the filling. If
the margin of the filling is clinically intact it is unlikely that active caries is
present beneath and the filling does not need to be replaced.
Bitewing radiographs
Bitewing radiographs are important in the diagnosis of recurrent caries
because this usually occurs cervically in the area of plaque stagnation
(Figure 3.20). It follows, therefore, that restorative materials should be
radio-opaque.
Sometimes a radiolucency on radiog raph indicates residual caries left when
the restoration was placed. Figure 3.21 shows a bitewing radiograph of an
amalgam restoration in a lower first molar with areas of radiodense dentine
beneath the restoration. This appearance represents residual demineralized
dentine left when the filling was originally placed. Tin and zinc ions from the
amalgam have passed into the demineralized area to give the radiodense
appearance. This restoration does not need to be replaced.