RECENT AIDS IN DIAGNOSIS OF DENTAL CARIES Various methods are being used for diagnosis of dental caries 1] Radiographic techniques a) Digital b) Xeroradiography 2] Electronic caries monitor (ECM) 3] Detection systems based on electrical current measurement 4] Optical caries detection techniques a) Optical coherence tomography (OCT) b) Polarized Raman Spectroscopy (PRS) 5] Enhanced visual techniques a) Fiber-Optic TransIllumination (FOTI) b) Digital Imaging Fiber-Optic TransIllumination (DIFOTI) 6] Fluorescent techniques a) Visible light fluorescence - QLF b) Laser fluorescence—DIAGNODent c) Infrared fluorescence. Current Concepts In Cariology Page 121
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Caries diagnosis is the art or act of identifying a disease
from its signs and symptoms.
TO DIAGNOSE OR TO DETECT?
The art of diagnosis rests on the assumption that
diseases can be identified from their signs and symptoms.
Diagnostic reasoning is an extremely complex process that
involves elements of simple pattern recognition,
probabilistic considerations and hypothetico-deductive
thinking. Diagnostic decision making is a balancing act.
The clinician must not overlook diseases in need of
treatment, and, at the same time, he must not make a
diagnosis when it is not warranted. The inherent complexity
of the diagnostic process explains why nobody has ever
been able to unveil how clinicians think when they examine
their patients and seek the right diagnosis. During the
diagnostic process the clinician attempts to assign a label to
a set of signs and symptoms brought together from various
sources (e.g. interview, clinical examination and
supplementary tests). This information is used to assess the
probability that the patient has a certain condition. In
medicine the diagnosis is a pivotal step for making
treatment decisions. Therefore, the diagnostic step has
sometimes been referred to as ‘a mental resting place on the
way to intervention’. Figure 8.1 illustrates the classical
diagnostic decision process as outlined above. 26
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FIG 8.1: THE CLASSICAL DIAGNOSTIC DECISION
PROCESS
Our understanding of the caries process has continued
to advance, with the vast majority of evidence supporting a
dynamic process which is affected by numerous modifiers
tending to push the mineral equilibrium in one direction or
another, i.e. towards remineralisation or demineralisation.
With this greater understanding of the disease, comes an
opportunity to promote ‘preventative’ therapies that
encourage the remineralisation of non-cavitated lesions
resulting in inactive lesions and the preservation of tooth
structure, function and aesthetics. Central to this vision is
the ability to detect caries lesions at an early stage and
correctly quantify the degree of mineral loss, ensuring that
the correct intervention is instigated. The failure to detect
early caries, leaving those detectable only at the deep
enamel, or cavitated stage has resulted in poor results and
outcomes for remineralisation therapies. A range of new
detection systems have been developed and are either
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currently available to practitioners or will shortly be made
so. These detection systems are therefore aimed at
augmenting the diagnostic process by facilitating either
earlier detection of the disease or enabling it to be
quantified in an objective manner.
Visual inspection, the most ubiquitous caries detection
system, is subjective. Assessment of features such as colour
and texture are qualitative in nature. These assessments
provide some information on the severity of the disease but
fall short of true quantification. They are also limited in
their detection threshold and their ability to detect early,
non cavitated lesions restricted to enamel is poor. It is this
ability to quantify and/or detect lesions earlier that the
novel diagnostic systems offer to the clinician.
Novel diagnostic systems are based upon the
measurement of a physical signal—these are surrogate
measures of the caries process. Examples of the physical
signals that can be used in this way include X-rays, visible
light, laser light, electronic current, ultrasound, and
possibly surface roughness. For a caries detection device to
function, it must be capable of initiating and receiving the
signal as well as being able to interpret the strength of the
signal in a meaningful way. Table 2 demonstrates the
physical principles and the detection systems that have
taken advantage of them. 27
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CLINICAL METHODS:
Visual detection of caries was described as early as
1801, in a book entitled “Skinner: A Treatise of Human
Teeth.” One of the most important early contributions to
diagnosis of dental caries came from G.V. Black. Black was
among the first to describe, in explicit detail, methods of
visual and tactile detection of dental caries as part of an
oral examination, including the cleaning and drying of teeth
and the use of explorers, that still are in use 100 years later.
For detection of proximal caries, Black described the use of
separators to directly visualize areas of concern and the use
of ligatures (dental floss) passed through the contact point
to detect surface roughness and breakdown. Black’s
diagnostic methods laid the groundwork for future criteria
for the detection of dental caries. Radike described detailed
criteria for the visual and tactile detection of dental caries
that until recently were used widely in epidemiologic and
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clinical research. They relied heavily on an explorer “catch”
for detection of caries on occlusal surfaces and recorded
cavitated lesions, but not noncavitated lesions. Since the
days of Black, our diagnostic understandings have been far
more advanced than simply diagnosing caries at the level of
cavitation. The latest contribution to visual diagnostic
criteria for caries is the International Caries Detection and
Assessment Criteria (ICDAS), the development of which
involved a joint effort of international cariologists. ICDAS
was designed to facilitate the standardized diagnosis of
caries on all tooth surfaces at all stages of severity. An
updated version of ICDAS (ICDAS II) has been well
accepted and been used in clinical studies with good
intraexaminer and interexaminer agreement, as well as
satisfactory sensitivity and specificity 28.
[1] RADIOGRAPHIC METHODS:
Less than six months after W.C. Roentgen’s discovery
of the x-ray, William J. Morton, a New York physician, was
one of the first to report that x-rays could have dental
applications. More recent developments include higher-
speed film and digital radiography. Current digital imaging
technologies generate images whose diagnostic yield may
equal, but not necessarily exceed, that of images obtained
by using conventional film 28.
A] DIGITAL RADIOGRAPHS
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Digital radiography has offered the potential to
increase the diagnostic yield of dental radiographs and this
has manifested itself in subtraction radiography. A digital
radiograph (or a traditional radiograph that has been
digitised) is comprised of a number of pixels. Each pixel
carries a value between 0 and 255, with 0 being black and
255 being white. The values in between represent shades of
grey, and it can be quickly appreciated that a digital
radiograph, with a potential of 256 grey levels has
significantly lower resolution than a conventional
radiograph that contain millions of grey levels. This would
suggest that digital radiographs would have a lower
diagnostic yield than that of traditional radiographs.
Research has confirmed this; with sensitivities and
specificities of digital radiographs being significantly lower
than those of regular radiographs when assessing small
proximal lesions.
However, digital radiographs offer the potential of
image enhancement by applying a range of algorithms, some
of which enhance the white end of the grey scale (such as
Rayleigh and hyperbolic logarithmic probability) and others
the black end (hyperbolic cube root function). When these
enhanced radiographs are assessed their diagnostic
performance is at least as good as conventional radiographs,
with reported values of 0.95 (sensitivity) and 0.83
(specificity) for approximal lesions. See Fig. 8.2 for an
example of this enhancement. When these findings are
considered, one must remember that digital radiographs
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offer a decrease in radiographic dose and thus offer
additional benefits than diagnostic yield. Digital images can
also be archived and replicated with ease. 27
FIG 8.2: COMPARISON OF REGULAR AND ENHANCED
DIGITAL RADIOGRAPHS. (A) DIGITAL RADIOGRAPH,
(B) ENHANCED RADIOGRAPH WHERE THE
INTERPROXIMAL LESIONS BETWEEN FIRST MOLAR
AND SECOND PREMOLAR CAN BE SEEN MORE
CLEARLY.
As described above, using digital radiographs offers a
number of opportunities for image enhancement, processing
and manipulation. One of the most promising technologies
in this regard is that of radiographic subtraction which has
been extensively evaluated for both the detection of caries
and also the assessment of bone loss in periodontal studies.
To perform subtraction radiography the images should be
taken using either a geometry stabilising system (i.e. a
bitewing holder) or software has been employed to register
the images together, then any differences in the pixel values
must be due to change in the object.
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Subtraction images therefore emphasise this change
and the sensitivity is increased. It is clear from this
description that the radiographs must be perfectly, or as
close to perfect as possible, aligned. Any discrepancies in
alignment would result in pixels being incorrectly
represented as change. Several studies have demonstrated
the power of this system, with impressive results for
primary and secondary caries. However, uptake of this
system has been low, presumably due to the need for well
aligned images. Recent advances in software have enabled
two images with moderate alignment to be correctly aligned
and then subtracted. This may facilitate the introduction of
this technology into mainstream practice where such
alignment algorithms could be built into practice software
currently used for displaying digital radiographs. An
example of a subtraction radiograph is shown in Fig. 8.3. 27
FIG. 8.3: EXAMPLE OF A SUBTRACTION OF TWO
DIGITAL BITEWING RADIOGRAPHS. (A) RADIOGRAPH
SHOWING PROXIMAL LESION ON MESIAL SURFACE
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Two radiographs of the same object can be compared using their pixel values.
The value of the pixels from the first object is subtracted from the second image.
If there is no change, the resultant pixel will be scored 0; any value that is not 0 must be attributable to either the onset or progression of demineralisation, or regression.
Recent Aids in Diagnosis of Dental Caries
OF FIRST MOLAR, (B) FOLLOW UP RADIOGRAPH
TAKEN 12 MONTHS LATER, (C) THE AREAS OF
DIFFERENCE BETWEEN THE TWO FILMS ARE SHOWN
AS BLACK, I.E. IN THIS CASE THE PROXIMAL LESION
HAS BECOME MORE RADIOLUCENT AND HENCE HAS
PROGRESSED
B] XERORADIOGRAPHY:
Mechanism: Xeroradiography is an electrostatic
process which uses an amorphous selenium photoconductor
material, vacuum deposited on an aluminium substrate, to
form a plate. The plate, enclosed in light tight cassette, may
be likened to films used in halide-based technique. The key
functional steps in the process involve the sensitization of
the photoconductor plate in the charging station by
depositing a uniform positive charge on its surface with a
corona-emitting device called scorotron. That is, the
uniform electrostatic charge placed on a layer of selenium
is in electrical contact with a grounded, conductive backing.
In the absence of electromagnetic radiation, the
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photoconductor remains nonconductive and with its uniform
electrostatic charge when radiation is passed through an
object which will vary the intensity of the radiation,
observed Rawls and Owen. The photoconductor will then
conduct its electrostatic charge into the grounded base in
proportion to the intensity of the exposure. After charging,
the cassette is inserted into a thin polyethylene bag to
protect the cassette and plate from saliva. The generated
latent image is developed through an electrophoretic
development process using liquid toner. The process
involves the migration to and subsequent deposition of
toner particles suspended in a liquid onto an image
reception under the influence of electrostatic field forces.
That is, by applying negatively charged powder (toner)
which is attracted to the residual positive charge pattern on
the photoconductor, the latent image is made visible and the
image can be transferred to a transparent plastic sheet or to
paper. The toner is thereafter fixed to a receiver sheet onto
which a permanent record is made. The plate is then cleaned
of toner for reuse. 30
POSSIBLE ADVANTAGES OF XERORADIOGRAPHY
ELIMINATION OF ACCIDENTAL FILM EXPOSURE :
the reasons being that large light intensity is required for
photoconduction and even when there is exposure, the
charged area intrinsically gets erased. As a result, there is
minimal need for storage for film protection during
processing.
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HIGH RESOLUTION : Xeroradiography has excellent
characteristics of the forces around the electrostatic charges
which form the latent image. The strengths of the fields are
smaller at the centre of charged ones than at the edge,
resulting in a greater number of powder particles
collections peripherally than in central charged areas. This
greatly enhances local contrast which, in turn, improves
resolution and image quality.
SIMULTANEOUS EVALUATION OF MULTIPLE
TISSUES
EASE OF REVIEWING USE OF REFLECTED OR
TRANSMITTED LIGHT is allowed by xeroradiography.
This is because the image can be mounted either in a
transparent plastic sheet or on opaque paper.
HIGHER LATITUDE OF EXPOSURE FACTORS: little
image quality change in xeroradiography will require large
kilo-voltage variations. The end point is that chances of
incorrect exposure and retakes are highly slim.
BETTER EASE AND SPEED OF PRODUCTION
EECONOMIC BENEFIT
REDUCED EXPOSURE TO RADIATION HAZARDS
WIDE APPLICATIONS
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POSSIBLE DISADVANTAGES OF
XERORADIOGRAPHY:
TECHNICAL DIFFICULTIES : Both the amount of
radiation exposure and the thickness of xeroradiographic
plate are linearly proportional. An increased thickness of
the plate will increase the speed, because of the greater
likelihood that the x-rays passing through the photo
conducting layer will interact.
FRAGILE SELENIUM COAT : the amorphous selenium
photoconductor is a highly electrically stable layer.
However, the layer is quite easily scratched.
Notwithstanding, it has been observed that the surface
shows good resistance to scratching, chipping and abrasion.
As a result, placement and retention in confined area like
the mouth would possibly be difficult.
SLOWER SPEED : comparatively, xeroradiography has a
lower speed than halide radiographs. This can be significant
when dealing with intraoral films. 30
[2] ELECTRONIC CARIES MONITOR (ECM):
MECHANISM: The ECM device employs a single, fixed-
frequency alternating current which attempts to measure the
‘bulk resistance’ of tooth tissue (see Fig. 5). This can be
undertaken at either a site or surface level. When measuring
the electrical properties of a particular site on a tooth, the
ECM probe is directly applied to the site, typically a
fissure, and the site measured. During the 5 s measurement
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cycle, compressed air is expressed from the tip of the probe
and these results in a collection of data over the
measurement period, described as a drying profile that can
provide useful information for characterising the lesion. An
example of this is shown in Fig. 8.4 While it is generally
accepted that the increase in porosity associated with caries
is responsible for the mechanism of action for ECM, there
are some points to consider:
(1) Do electrical measurements of carious lesions measure
the volume of the pores, and if so, is it the total pore
volume or just a portion, perhaps the superficial portion,
that is measured? (2) Do electrical measurements measure
pore depth? If this is the case, what happens during
remineralisation where the superficial layer may
remineralise, leaving a pore beneath?
(3) Is the morphological complexity of the pores a factor in
the measurement of conductivity?
There are also a number of physical factors that will affect
ECM results. These include such things as the temperature
of the tooth, the thickness of the tissue, the hydration of the
material (i.e. one should not dry the teeth prior to use) and
the surface area. 27
FIG. 8.4: A DEMONSTRATION OF AN ECM PROFILE
OBTAINED FROM A PRIMARY ROOT CARIES LESION
IN VITRO DEMONSTRATING THE SITES ASSESSED.
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FIG.8.5 – THE ECM DEVICE (VERSION 4) AND ITS
CLINICAL APPLICATION. (A) THE ECM MACHINE, (B)
THE ECM HANDPIECE, (C) SITE SPECIFIC
MEASUREMENT TECHNIQUE, (D) SURFACE SPECIFIC
MEASUREMENT TECHNIQUE.
The reproducibility of the device has been assessed in
a number of publications and has been rated as good to
excellent for both measurement techniques. A clinical trial
has been undertaken using the ECM device on root caries,
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and the successful outcome of this study suggests that
dentine may be a more suitable tissue for ECM. The study
assessed the effect of 5000 ppm fluoride dentifrice against
1100 ppm on 201 subjects with at least 1 root caries lesion.
These were site specific measurements taken using the
airflow function of the ECM unit. After 3 and 6 months,
there was statistical difference between the two groups,
with the higher fluoride group showing a better
remineralising capability than the lower fluoride paste
users21 (see Fig 8.6). This is good evidence to suggest that
ECM is capable of longitudinal monitoring and that
clinicians may be able to employ the device to monitor
attempts at remineralising, and thus potentially arresting,
root caries lesions in their patients. 27
FIG. 8.6: ECM VALUES FROM A ROOT CARIES STUDY
USING HIGH AND LOW CONCENTRATIONS OF
FLUORIDE DENTIFRICES. THE INCREASING ECM
VALUES RELATE TO A REDUCTION IN POROSITY
AND INCREASE IN ELECTRICAL RESISTANCE.
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A further application of electronic monitoring of
caries is that of Electrical Impedance Spectroscopy or EIS.
Unlike ECM which uses a fixed frequency (23 Hz), EIS
scans a range of electrical frequencies and provides
information on capacitance and impendence among others.
This process provides the potential for more detailed
analysis of the structure of the tooth to be developed,
including the presence and extent of caries. 27
[3] DETECTION SYSTEMS BASED ON ELECTRICAL
CURRENT MEASUREMENT :
Every material possesses its own electrical signature;
i.e. when a current is passed through the substance the
properties of the material dictate the degree to which that
current is conducted. Conditions in which the material is
stored or physical changes to the structure of the material
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will have an effect on this conductance. Biological
materials are no exception and the concentration of fluids
and electrolytes contained within such materials largely
govern their conductivity 27.
For example, dentine is more conductive than enamel.
In dental systems, there is generally a probe, from which
the current is passed, a substrate, typically the tooth, and a
contra-electrode, usually a metal bar held in the patient’s
hand. Measurements can be taken either from enamel or
exposed dentine surfaces. In its simplest form, caries can be
described as a process resulting in an increase in porosity of
the tissue, be it enamel or dentine. This increased porosity
results in a higher fluid content that sound tissue and this
difference can be detected by electrical measurement by
decreased electrical resistance or impedance 27.
[4] OPTICAL CARIES DETECTION TECHNIQUES:
Optical caries detection methods are based on
observation of the interaction of energy which is applied to
the tooth, or the observation of energy which is emitted
from the tooth. Such energy is in the form of a wave in the
electromagnetic spectrum. In its simplest form, caries can
be described as a process resulting in structural changes to
the dental hard tissue. The diffusion of calcium, phosphate,
and carbonate out of the tooth, the demineralisation
process, will result in loss of mineral content. The resultant
area of demineralised tooth substance is filled mainly by
bacteria and water. The porosity of this area is greater than
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that of the surrounding structure. Increased scattering of
incident light due to this structural change appears to the
human eye as a so called white spot. Hence, the caries
process leads to distinct optical changes that can be
measured and quantified with advanced detection methods
based on light that shines on and interacts with the tooth 29.
SCATTERING : Scattering is the process in which the
direction of a photon is changed without loss of energy. The
incident light is forced to deviate from a straight path when
it interacts with small particles or objects in the medium
through which the light passes. In physical terms scattering
is regarded as a material property. A glass of milk is seen
as white because incident light on the milk is scattered in
all directions, leaving the milk without absorption. Snow
appears white because light incident in the snow is scattered
in all directions by the small ice crystals. Light of all
visible wavelengths exits snow without suffering
absorption. Scattering is highly wavelength sensitive,
shorter wavelengths scatter much more than longer ones.