Dental caries is one of the most prevalent chronic diseases of humans worldwide. When
different stages of the disease are taken into account, from the initial to the clinically
manifest lesion, very few individuals are truly unaffected. In most industrialized countries
60%–90% of school-aged children are affected. The prevalence among adults is even higher and
in most countries the disease affects nearly 100% of the population .
During the last thirty years, however, major changes have occurred in the pattern of the
disease. Progression of enamel caries is now slower , allowing time for preventive
intervention before irreversible destruction of tooth substance occurs. During the early
stages of the disease the process is reversible and can be arrested: noninvasive intervention
can convert a lesion from an active to an inactive state [3, 4]. Appropriate diagnostic
techniques are necessary to support such decisions about management of the individual lesion.
The clinician needs to be able to monitor the outcome of noninvasive measures and in cases
where there is evidence of lesion progression, make a timely decision to intervene, using
minimally invasive techniques and restoring damaged tooth structure without weakening the
tooth. Applying strategies to control, arrest, or reverse the disease process can reduce the
economic burden, pain, and suffering of placing and replacing restorations .
This modern, conservative approach to clinical management of dental caries, which has been
evolving during the past twenty years, has necessitated a critical appraisal of methods used
today for clinical detection of carious lesions.
Complementing traditional diagnostic methods with advanced, more sensitive methods will
improve caries diagnostic routines and hence the dental care and treatment of patients. The
application of such complementary methods should offer objective information about the
presence and severity of a lesion, to complement the clinician’s subjective interpretation,
providing evidence-based clinical caries diagnosis. In this context, there is also a place
for more sensitive caries detection methods in clinical caries research. Clinical trials in
which lesions are monitored in thousands of subjects over several years are no longer
commercially viable. A quantitative method capable of measuring small changes would allow
trials of much shorter duration and fewer subjects [6, 7].
Conventional examination for caries detection is based primarily on subjective interpretation
of visual examination and tactile sensation, aided by radiographs. The clinician makes a
dichotomous decision (absence or presence of a lesion) based on subjective interpretation of
color, surface texture, and location, using rather crude instruments such as a dental
explorer and bitewing radiographs . Studies based on these methods often show low
sensitivity and high specificity, that is, a large number of lesions may be missed [9–13].
Sensitivity and specificity are widely used measures to describe and quantify the diagnostic
ability of a test . In the context of caries research, sensitivity is a measure of the
method’s ability to correctly identify all surfaces damaged by caries, and specificity the
measure of correctly identified all sound surfaces. Sensitivity and specificity are expressed
as values between 0 and 1 (100%), values closer to 1 indicating a high quality result. For
caries diagnostic methods, values should be at least 0.75 for sensitivity and over 0.85 for
Diagnostic techniques are also evaluated in terms of validity and reliability. To determine
validity, the outcome as measured by the method is compared with a reference standard, a
‘‘true’’ situation. Reliability expresses the consistency of a set of measurements performed
with the method. High validity is considered to confirm the absence of systematic errors and
high reliability the absence of random errors of the method. The generalisability of a
diagnostic technique is also described in terms of external and internal validity. The
external validity reflects the extent to which the results of a study can be extrapolated to
other subjects or settings, whereas internal validity reflects the degree to which
conclusions about causes or relationships are likely to be true, in view of the measures
used, the research setting, and the overall study design. Good experimental design will
filter out the most confounding variables, which could compromise the internal validity of an
A wide variation in terms of sensitivity and specificity for conventional caries detection
methods are found in the literature [9, 16, 17]. An overall low sensitivity of less than 0.50
is reported, which means that a guess would provide the same result when we correctly want to
identify a caries lesion. A recently published comprehensive review  stated that the
evaluations of diagnostic performance are based on limited numbers of studies of questionable
internal and external validity attributable to incomplete descriptions of selection and
diagnostic criteria and observer reliability. The quality of published studies is further
compromised by the use of small numbers of observers, nonrepresentative teeth, samples with
high lesion prevalence, a variety of reference standards of unknown reliability, and
variations in statistical analysis of the reported results.
It is apparent that conventional methods for the detection of dental caries do not fulfill
the criteria for an ideal caries detection method. These methods rely on subjective
interpretation and are insensitive to early caries detection. It is widely recognised that
the current methods cannot detect caries lesions until a relatively advanced stage, involving
as much as one-third or more of the thickness of enamel .
The shortcomings of conventional caries detection methods and the need for supplementary
methods have long been acknowledged. The series of published proceedings from the three
“Indiana Conferences on Early Detection of Dental Caries” contains a wealth of detail of work
in this area [19–21]. Over the past twenty years there has been intensive research into more
sophisticated methods for early detection of dental caries [5, 7–9, 16, 17, 22–34]. There are
a number of optical caries detection methods and some are summarized in Table 1. Several are
in their infancy and there is significant work involved in developing these techniques.
Therefore, validation studies are essential to determine their clinical utility before
implementation in clinical practice.
Table 1: Summary of optical caries detection methods.
An initial effect of the caries disease process, increased porosity, results in a distinct
change in the optical properties of the affected dental tissue, providing objective evidence
of a caries-induced change. Caries detection methods based on changes in a specific optical
property are referred to in the literature as optically based methods, optical methods, or
dental tissue optics. The methods are based on the measurement of a physical signal, derived
from the interaction of light with dental hard tissue. The following section presents a brief
description of the principles underlying these methods.
Copyright © 2010 Lena Karlsson. This is an open access article distributed under the Creative
Commons Attribution License, which permits unrestricted use, distribution, and reproduction
in any medium, provided the original work is properly cited.