Recent Aids in diagnosis of dental caries
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Transcript of Recent Aids in diagnosis of dental caries
Recent Aids in Diagnosis of Dental Caries
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.
7] Transillumination with Near-Infrared light.
8] Near-Infrared reflectance imaging.
9] Terahertz Pulse Imaging.
10] Multiphoton Imaging.
11] Time-Correlated Single- Photon counting fluorescence
Lifetime Imaging
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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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Recent Aids in Diagnosis of Dental Caries
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.
Therefore, caries detection methods employing wavelengths
in the visible range of the electromagnetic spectra (400 nm
to 700 nm) are highly limited by scattering. An early
enamel lesion looks whiter than the surrounding healthy
enamel because of strong scattering of light within the
lesion. Methods measuring lesion severity are based on
differences in scattering between sound and carious
enamel29.
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ABSORPTION WITH FLUORESCENCE: Absorption is
the process in which photons are stopped by an object and
the wave energy is taken in by the object. The energy lost is
mostly converted into heat or into another wave which has
less energy and hence longer wavelengths. In physical terms
absorption is also regarded as a material property. The
previous analogy of the glass of milk appearing white can
be extended to a cup of tea; the tea is seen as transparent
because it does not scatter light, but it looks brown because
much of the light is absorbed by the tea. Likewise, mud and
pollution in white snow can be seen as dark spots because
certain wavelengths are absorbed by these polluted spots.
Absorption of light in tissue is strongly dependent on the
wavelength. Water is an example of a strong absorber in the
infrared range. After absorption the energy can be released
by emission of light at a longer wavelength, through the
process of fluorescence. Fluorescence occurs as a result of
the interaction of the wavelength illuminating the object
and the molecule in this object. The energy is absorbed by
the molecule with subsequent electronic transition to the
next state, to a higher level state where the electrons remain
for a short period of time. From here the electrons may fall
back to the ground state and release the gained energy in
terms of longer wavelength and colour, which is related to
the energy given off and fluorescent light can be emitted.
Autofluorescence, the natural fluorescence of dental hard
tissue without the addition of other luminescent substances
has been known for a long time. Demineralisation will
result in loss of autofluorescence which can be quantified
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using caries detection methods based on the differences in
fluorescence between sound and carious enamel. 29
[A] OPTICAL COHERENCE TOMOGRAPHY (OCT):
OCT can be defined as optical inferometric technique
to create cross sectional images of scattering media. There
are various functional techniques developed in OCT.
They are 1) Polarisation sensitive Optical coherence
tomography (PSOCT)
2) Doppler OCT
3) Wave length dependent OCT
Among these PS-OCT is popular. Studies of light
propagation in dental tissue using PS-OCT revealed strong
birefingence in enamel and anisotropic light propagation
through dentinal tubules. Amaechi et al used the area under
the LCI signal as a measure of the degree of reflectivity of
the tissue and showed that this area is related to the amount
of mineral loss, and increases with increasing
demineralization time. Hence, OCT could possibly be used
to quantitatively monitor the mineral changes in a caries
lesion. In the early investigations, birefringence induced
artefacts in the enamel OCT image. These were eliminated
by measuring the polarization state of the returned light.
Birefringence detected by PS-OCT, however, has been
shown to be useful as a contrast agent indicating precarious
or carious lesions in both enamel and dentin 29.
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Baumgartner et al showed that PS-OCT can provide
additional information related to the mineralization status
and/or the scattering properties of the dental materials. The
studies demonstrated that PS-OCT is well suited for the
imaging of interproximal and occlusal caries, early root
caries, and for imaging decay under composite fillings.
Longitudinal measurements of the reflected light intensity
in the orthogonal polarization state from the area of
simulated caries lesions linearly correlated with the square
root of time of demineralization indicating that PS-OCT is
well suited for monitoring changes in enamel mineralization
over time. OCT provides high resolution morphological
depth imaging of incipient caries. With OCT, early lesions
can be readily identified as regions of high light
backscattering with depth into the enamel as compared to
healthy sound enamel. From the OCT images, the lesion
depth can be approximated to provide clinically useful
information to guide treatment decisions. In addition, there
is a derived parameter known as the optical attenuation
coefficient in order to distinguish sound from carious
enamel non-subjectively. OCT is being combined with
Polarized Raman Spectroscopy (PRS) since regions of high
light backscattering not related to caries development can
lead to false-positive results. PRS provides biochemical
specificity along with molecular structural/orientational
information. With PRS, the Raman depolarization ratio
calculated from the main phosphate vibration at ~959 cm-1
from parallel- and crosspolarized Raman spectra allows
discrimination between sound and early developing caries.
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In combination, OCT and PRS have potential for detecting
and monitoring early lesions with high sensitivity and high
specificity. 29
[B] POLARIZED RAMAN SPECTROSCOPY (PRS):
OCT imaging in regions of hypocalcification can
sometimes show increased light back-scattering at the
surface, which could be misinterpreted as signs of early
caries. To help rule out such false-positive readings and
increase the specificity of this method, OCT and PRS have
been coupled to obtain biochemical information for
confirmation of caries. PRS provides details on the
molecular composition (e.g., collagen in dentin vs.
predominantly inorganic apatite in enamel) and molecular
structure of cells and tissues. Like OCT, PRS measures
light scattering. Although most scattered photons have the
same energy and wavelength as the incoming excitation
light, about 1 in 107 photons scatter at energy different
from that of the incoming light. This energy difference is
proportional to the vibrational energy of the scattered
molecules within the sample and is known as the Raman
Effect. As with other emerging optical methods, the
properties of the scattered light within sound or porous
carious regions are being explored to determine their use in
caries detection. In fluorescence-based techniques, there are
a limited number of intrinsic fluorophores that can provide
diagnostic information without the addition of external
dyes. In contrast, PRS can provide information not only
about bacterial porphyrins leached into carious regions, but
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also about the primary mineral matrix and, thus, the state of
demineralization or remineralisation of the tooth. This
information is gathered without the need to add extrinsic
dyes or agents. PRS provides information on the
composition, crystallinity and orientation of the mineral
matrix, all of which are affected in caries formation or
remineralization. 4
[5] ENHANCED VISUAL TECHNIQUES
[A] FIBRE OPTIC TRANSILLUMINATION (FOTI):
The basis of visual inspection of caries is based upon
the phenomenon of light scattering. Sound enamel is
comprised of modified hydroxyapatite crystals that are
densely packed, producing an almost transparent structure.
The colour of teeth, for example, is strongly influenced by
the underlying dentin shade. When enamel is disrupted, for
example in the presence of demineralisation, the penetrating
photons of light are scattered (i.e. they change direction,
although do not loose energy) which results in an optical
disruption. In normal, visible light, this appears as a
‘whiter’ area—the so called white spot. This appearance is
enhanced if the lesion is dried; the water is removed from
the porous lesion. Water has a similar refractive index (RI)
to enamel, but when it is removed, and replaced by air,
which has a much lower RI than enamel, the lesion is shown
more clearly. This demonstrates the importance of ensuring
the clinical caries examinations are undertaken on clean,
dry teeth. Fibre optic transillumination takes advantage of
these optical properties of enamel and enhances them by
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using a high intensity white light that is presented through a
small aperture in the form of a dental hand piece. Light is
shone through the tooth and the scattering effect can be
seen as shadows in enamel and dentine, with the device’s
strength the ability to help discriminate between early
enamel and early dentine lesions (see Fig. 7). A further
benefit of FOTI is that it can be used for the detection of
caries on all surfaces; and is particularly useful at proximal
lesions27.
The diagnosis of approximal carious lesions has been
primarily through visual clinical examination. However, in
situations where the teeth are normally in anatomical
contact with others, it is a very difficult task for the dentist
to detect caries in posterior teeth by that exam, resulting in
a high proportion of false negative decisions. Conventional
bitewing radiography remains the most common diagnostic
aid because it has been shown to enhance the detection of
approximal lesions. However, there are some problems
associated with this technique, for example, if the
horizontal angulation is incorrect, overlapping of
approximal surfaces will occur on the radiograph. Other
problem is the incapacity of method to distinguish
noncavitated from cavitated lesions. Fibre-optic
transillumination (FOTI) has been investigated as an
alternative method for the detection of approximal carious
lesions. In this method, a white light from a cold-light
source is passed through a fibre to an intraoral fibre-optic
light probe that is placed on the buccal or lingual side of
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the tooth and the surfaces are examined through transmitted
light, which is viewed from the occlusal surface. A carious
lesion has a lowered index of light transmission and so
appears as a darkened shadow when transilluminated. FOTI
is a simple, non-invasive, and painless procedure that can
be used repeatedly with no risk to the patient. In the
literature, the validity of diagnoses made with FOTI has
usually been assessed by comparison with the radiographic
diagnosis of the same surface, although it is well known
that radiography itself is not an accurate method 29.
Fibre optic consists of a halogen lamp and a rheostat
to produce a light of variable intensity. Two attachments
are used; a plane mouth mirror mounted on a steel cuff and
a fibre optic probe of 0.5 mm diameter so that it can be
placed in embrasure region. It produces a narrow beam of
light for transillumination. The rheostat is set to give a light
of maximum intensity. For examination the tip of the probe
is placed in the embrasure immediately beneath the contact
point of the proximal surface to be examined either on the
buccal or lingual surface depending on the tooth. The
marginal ridge is viewed from the occlusal surface. A
shadow extending to the dentinoenamel junction beneath the
marginal ridge may be evident if there is a break in the
integrity of the enamel of marginal ridge. 4
One would expect that FOTI would enable
discrimination of occlusal lesions to be improved
(particularly dentine lesions), as well as detection of
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proximal lesions (in the absence of radiographs) to be
higher. As a technique FOTI is an obvious choice for
translation into general practice; the equipment is
economical, the learning curve is short and the procedure is
not time consuming. However with the simplicity of the
FOTI system come limitations; the system is subjective
rather than objective, there is no continuous data outputted
and it is not possible to record what is seen in the form of
an image. In order to address some of these concerns, an
imaging version of FOTI has been developed; digital
imaging FOIT (DiFOTI). 27
[B] DIGITAL IMAGING FIBER OPTIC
TRANSILLUMINATION (DIFOTI)
This is a relatively new methodology that was adopted
in an attempt to reduce the perceived shortcomings of FOTI
by combining FOTI and a digital charge-coupled device
(CCD) camera. Digital Imaging Fiber-Optic
TransIllumination (DIFOTI) has been introduced to improve
early detection of carious surfaces. DIFOTI uses fiber-optic
transillumination of safe visible light to image the tooth.
DIFOTI uses visible light and not the ionising radiation and
is approved by US food and drug administration for caries
detection on approximal smooth and occlusal surface as
well as recurrent caries. DIFOTI uses scattering of light by
carious tissue as a method of distinguishing it from healthy
enamel the carious part of the tooth appears to be dark
against the light background of healthy tooth. 29
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Schneiderman et al.24 found that DIFOTI technique
has superior sensitivity over conventional radiographic
methods for detection of approximal, occlusal, and smooth
surface caries, and specificity was slightly less in general.
It has all the advantages of FOTI and also it has overcome
the disadvantage of FOTI as images in this technique can be
stored for future reference. 29
FIG. 8.7: FOTI EQUIPMENT
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Light delivered by a fiber-optic is collected on the other side of the tooth by a mirror system and fed to a digital electronic CCD.
Then the acquired data are sent to a computer for analysis with dedicated algorithms, which produce digital images that can be viewed by the clinician
and patient in real time or stored for later use.
Recent Aids in Diagnosis of Dental Caries
FIG. 8.8: EXAMPLE OF FOTI ON A TOOTH. (A)
NORMAL CLINICAL VISION, (B) WITH FOTI.
[6] FLUORESCENT TECHNIQUES
[A] VISIBLE LIGHT FLUORESCENCE—QLF:
Quantitative light-induced fluorescence (QLF) is a
visible light system that offers the opportunity to detect
early caries and then longitudinally monitor their
progression or regression. Using two forms of fluorescent
detection (green and red) it may also be able to determine if
a lesion is active or not, and predict the likely progression
of any given lesion. Fluorescence is a phenomenon by
which an object is excited by a particular wavelength of
light and the fluorescent (reflected) light is of a larger
wavelength. When the excitation light is in the visible
spectrum, the fluorescence will be of a different colour. In
the case of the QLF the visible light has a wavelength (l) of
370 nm, which is in the blue region of the spectrum. The
resultant auto-fluorescence of human enamel is then
detected by filtering out the excitation light using a band
pass filter at l > 540 nm by a small intra-oral camera. This
produces an image that is comprised of only green and red
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channels (the blue having been filtered out) and the
predominate colour of the enamel is green.
Demineralisation of enamel results in a reduction of this
auto-fluorescence. This loss can be quantified using
proprietary software and has been shown to correlate well
with actual mineral loss. The source of the auto-
fluorescence is thought to be the enamel dentinal junction—
the excitation light passes through the transparent enamel
and excites fluorophores contained within the EDJ. Studies
have shown that when underlying dentine is removed from
the enamel, fluorescence is lost, although only a small
amount of dentine is required to produce the fluorescence
seen. Decreasing the thickness of enamel results in a higher
intensity of fluorescence. The presence of an area of
demineralised enamel reduced the fluorescence for two
main reasons. The first `is that the scattering effect of the
lesion results in less excitation light reaching the EDJ in
this area, and the second is that any fluorescence from the
EDJ is back scattered as it attempts to pass through the
lesion.27
The QLF equipment is comprised of a light box
containing a xenon bulb and a hand piece, similar in
appearance to an intraoral camera, [see Fig. 8]. Light is
passed to the hand piece via a liquid light guide and the
hand piece contains the band pass filter. Live images are
displayed via a computer and accompanying software
enables patient’s details to be entered and individual images
of the teeth of interest to be captured and stored. QLF can
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image all tooth surfaces except inter- proximally. [See
Fig.8.9] for an example of QLF images that have been
merged to create a montage on the anterior teeth
demonstrating resolution of buccal caries over a 1 month
period following supervised brushing. Once an image of a
tooth has been captured, the next stage is to analyse any
lesions and produce a quantitative assessment of the
demineralisation status of the tooth. This is undertaken
using proprietary software and involves using a patch to
define areas of sound enamel around the lesion of interest.
Following this the software uses the pixel values of the
sound enamel to reconstruct the surface of the tooth and
then subtracts those pixels which are considered to be
lesion. This is controlled by a threshold of fluorescence
loss, and is generally set to 5%. This means that all pixels
with a loss of fluorescence greater than 5% of the average
sound value will be considered to be part of the lesion.
Once the pixels have been assigned ‘‘sound’’ or ‘‘lesion’’
the software then calculates the average fluorescence loss in
the lesion, known as %DF, and then the total area of the
lesion in mm2, a the multiplication of these two variables
results in a third metric output, DQ. See Fig. 8.10 for an
example of the analysis and the resultant lesion. When
examining lesions longitudinally, the QLF device employs a
video repositioning system that enables the precise
geometry of the original image to be replicated on
subsequent visits. QLF has been employed to detect a range
of lesion types. Smooth surfaces, secondary caries and
demineralisation adjacent to orthodontic brackets have all
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been examined. The reliability of both stages of the QLF
process; i.e. the image capture and the analysis; have been
examined and has been shown to be substantial. The QLF
system offers additional benefits beyond those of very early
lesion detection and quantification. The images acquired
can be stored and transmitted, perhaps for referral purposes,
and the images themselves can be used as patient motivators
in preventative practice.
FIG. 8.8: QLF EQUIPMENT. (A) THE QLF UNIT LIGHT
BOX, DEMONSTRATING THE HANDPIECE AND
LIQUID LIGHT GUIDE; (B) A CLOSE-UP OF THE
INTRA-ORAL CAMERA FEATURING A DISPOSABLE
MIRROR TIP THAT ALSO ACTS AS AN AMBIENT
LIGHT SHIELD.
For clinical research use, the ability to remotely
analyse lesions enables increased legitimacy in trials;
permitting, for example, a repeat of the analyses to be
conducted by a third-party. QLF is one of the most
promising technologies in the caries detection stable at
present, although further research is required to
demonstrate its ability to correctly monitor lesion changes
over time. There is also a great deal of interest in red
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fluorescence, and whether or not this can be a predictor of
lesion activity and again, research is currently being
undertaken in this area. 27
FIG.8.9: EXAMPLE OF QLF IMAGES. (A) WHITE LIGHT
IMAGE OF EARLY BUCCAL CARIES EFFECTING THE
MAXILLARY TEETH, (B) QLF IMAGE TAKEN AT THE
SAME TIME AS (A), NOTE THE IMPROVED
DETECTION OF LESIONS AS A RESULT OF THE
INCREASED CONTRAST BETWEEN SOUND AND
DEMINERALISED ENAMEL, (C) 6 MONTHS AFTER THE
INSTITUTION OF AN ORAL HYGIENE PROGRAMME,
THE LESIONS HAVE RESOLVED. 27
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FIG. 8.10: AN EXAMPLE OF LESION ANALYSIS USING
QLF. (A) LESION ON THE OCCLUSAL SURFACE OF A
PREMOLAR IS IDENTIFIED AND THE ANALYSIS
PATCH PLACED ON SOUND ENAMEL, (B) THE
RECONSTRUCTION DEMONSTRATES CORRECT
PATCH PLACEMENT AS THE SURFACE NOW LOOKS
HOMOGENOUS, (C) THE ‘SUBTRACTED’ LESION IS
DEMONSTRATED IN FALSE COLOUR INDICATING
THE SEVERITY OF THE DEMINERALISATION, (D) THE
QUANTITATIVE OUTPUT FROM THIS ANALYSIS AT A
VARIETY OF FLUORESCENT THRESHOLD LEVELS. 27
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[B] LASER FLUORESCENCE—DIAGNODENT:
The DIAGNODent (DD) instrument (KaVo, Germany)
is another device employing fluorescence to detect the
presence of caries. Using a small laser the system produces
an excitation wavelength of 655 nm which produces a red
light. This is carried to one of two intra-oral tips; one
designed for pits and fissures, and the other for smooth
surfaces. The tip both emits the excitation light and collects
the resultant fluorescence. Unlike the QLF system, the DD
does not produce an image of the tooth; instead it displays a
numerical value on two LED displays. The first displays the
current reading while the second displays the peak reading
for that examination. A small twist of the top of the tip
enables the machine to be reset and ready for another site
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examination and a calibration device is supplied with the
system. There has been some debate over what exactly the
DD is measuring; it is not employing the intrinsic changes
within the enamel structure in the same way as QLF; this
has been demonstrated by the inability of DD to detect
artificial lesions in in-vitro settings. Instead the system is
thought to measure the degree of bacterial activity; and this
is supported by the fact that the excitation wavelength is
suitable for inducing fluorescence from bacterial
porphyrins; a by product of metabolism (Fig 8.11). Initial
evaluations of the device suggest that it may be a promising
tool for clinical use. However, the device is not without its
confounders, and, like many novel caries detection devices,
requires teeth to be clean and dry. The presence of stain,
calculus, plaque and, when used in the laboratory, the
storage medium, have all be shown to have an adverse
effect on the DD readings. Most confounders tend to cause
an increase in the DD reading, leading to false-positives.
The literature surrounding the DD device was recently
assessed in a systematic review. The authors found that, for
dentinal caries, the DD device performed well, although
there was a great deal of heterogeneity in the studies and
they were all undertaken in vitro. The authors stated that
these results could not be extrapolated into the clinical
setting and then detected a worrying trend for the device to
produce more false-positives than traditional diagnostic
systems. Their conclusion was therefore that there was
insufficient evidence to support the use of the device as a
principle means of caries diagnosis in clinical practice. It
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should be noted that the DD device has not been employed
in a clinical trial, so there are no data indicating that the
system can detect a dose response. 27
FIG 8.11: THE DIAGNODENT DEVICE.
[C] INFRARED FLUORESCENCE:
In theory, the tooth is exposed to light (irradiation)
with a wavelength of between 700 and 15,000 nm. Barrier
filters are used to observe any resulting fluorescence.
Studies by Alfano et al. mention exposure of teeth to
wavelengths exceeding 700 nm, but the results were not
presented. Unpublished reports commented upon by
Longbottom suggest that the technique is able to
discriminate between sound and carious enamel and dentin.
Further work is required to determine if the fluorescence
signal from exposure to infrared irradiation is greater than
that from other wavelengths. Additionally, any heating
effects from absorption of infrared irradiation may have
potentially damaging effects on the dental pulp, given the
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increased penetration and decreased scattering of the longer
wavelength. Specific coherent sources of such irradiation
have been relatively difficult to acquire, and detection
involves the use of infrared-sensitive detectors as CCDs or
film29.
[7] TRANSILLUMINATION WITH NEAR-INFRARED
LIGHT:
The caries lesion may also be examined by shining
white light through the tooth. Wavelengths in the visible
range (400–700 nm) are limited by strong light scattering,
making it difficult to image through more than 1 mm or 2
mm of tooth structure. Therefore, methods employing
wavelengths in the visible range of the electromagnetic
spectra (400–700 nm) such as QLF (λ > 520 nm), LF (λ =
655 nm), and Digital Imaging Fibre-Optic Transillumination
(DIFOTI) which uses high intensity white light, are highly
limited by scattering. Methods that use longer wavelengths,
such as in the NIR spectra (780-1550 nm), can penetrate the
tissue more deeply. This deeper penetration is crucial for
the transillumination (TI) method. Research has shown that
enamel is highly transparent in the NIR range (750 nm-1500
nm) due to the weak scattering and absorption in dental
hard tissue at this wavelengths. 29
FIG 8.12: TRANSILLUMINATION (TI) WITH NEAR-
INFRARED (NIR) LIGHT. EXPERIMENTAL SET-UP OF
THE TI SYSTEM. THE TOOTH IS ILLUMINATED WITH
NIR LIGHT. POLARIZERS ARE USED TO
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EXPERIMENTALLY BLOCK OUT THE AMBIENT LIGHT
FROM SATURATING THE DETECTOR, A CHARGE
COUPLE DEVICE (CCD). 30
[8] NEAR-INFRARED REFLECTANCE IMAGING:
In this technique, the tooth is exposed to light
(irradiation) with a wave length of between 700 and 1500
nm. Light scattering in sound dental enamel decreases
markedly in the NIR region and studies have shown that
enamel has the highest transparency near 1310 nm. At this
wavelength, the attenuation coefficient is only 2 to 3 cm−1,
which is a factor of 20 to 30 times lower than in the visible
region. At longer wavelengths, water absorption increases
significantly and reduces the penetration of the NIR light.
Even though the light scattering for sound enamel is at a
minimum in the NIR, the light scattering coefficient of
enamel increases by 2-3 order of magnitudes upon
demineralization due to the formation of pores on a similar
size scale to the wavelength of the light that act as Mie
scatterers. Therefore, caries lesions can be imaged with
optimal contrast at 1310 nm. And detection is done by
infrared sensitive detectors as CCD or film. According to
Christian Zakian et al a sensitivity of > 99% and a
specificity of 87.5% for enamel lesions and a sensitivity of
80% and a specificity > 99% for dentine lesions. The nature
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of the technique offers significant advantages, including the
ability to map the lesion distribution rather than obtaining
single point measurements, it is also non-invasive,
noncontact, and stain insensitive. These results suggest that
NIR spectral imaging is a potential clinical technique for
quantitative caries diagnosis and can determine the presence
of occlusal enamel and dentin lesions. 29
[9] TERAHERTZ PULSE IMAGING:
This method uses waves with tetrahertz frequency
(=1012 Hz or a wavelength of approximately 30μm) for an
image to be obtained by tetrahertz irradiation, the object is
placed in the path of the beam. It is possible to record
tetrahertz images using CCD detector. It has no adverse
thermal effects, it is non ionising low signal to noise ratio,
but the cost of equipment is high, and careful interpretation
is required. Dental Applications for this technique have
been limited but promising. Longitudinal sections through
three teeth have demonsrated increased terahertz absorption
by early occlusal caries and an apparent ability to
discriminate dental caries from idiopathic enamel
hypomineralisation. Work in progress to image intact teeth
with early carious lesion. 29
[10] MULTIPHOTON IMAGING:
Infra red light of 850 nm has been used for
multiphoton imaging of teeth. In conventional fluorescence
imaging (QLF), a single blue photon is used to excite a
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fluorescent compound in the tooth. In the multiphoton
technique two infrared photons (with half the energy of blue
photon) are absorbed simultaneously. With this technique,
sound tooth tissue fluoresces strongly, whereas carious
tooth tissue fluoresces to a much lesser extent. In practice,
by using motors with micron accuracy, one can move the
plane of focus through the tissue and record the sectional
images from the tooth to form a 3D image. Caries will
appear as a dark form with in a brightly fluorescing tooth.
To highlight the diseased tissue, the image may be
displayed in its negative form so that caries appear bright
with in dark tooth. 29
[11] TIME-CORRELATED SINGLE-PHOTON
COUNTING FLUORESCENCE: LIFETIME IMAGING:
It has also been demonstrated that fluorescence
lifetime imaging microscopy (FLIM) has the ability to
distinguish the carious region from sound dental tissue.
Optical band pass interference filters were then applied to
this broad-bandwidth source to select the 488 nm excitation
wavelength required to perform TCSPC FLIM of dental
structures. The white-light generation source provides a
flexible method of producing variable-bandwidth visible
and ps-pulsed light for TCSPC FLIM. The results from the
dental tissue indicate a potential method of discriminating
diseased tissue from sound, but stained tissue, which could
be of crucial importance in limiting tissue resection during
preparation for clinical restorations. 29
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