Review
Caries detection and diagnosis: Novel technologies
Iain A. Pretty *
Dental Health Unit, 3A Skelton House, Lloyd Street North, Manchester Science Park, Manchester M15 6SH, UK
j o u r n a l o f d e n t i s t r y 3 4 ( 2 0 0 6 ) 7 2 7 – 7 3 9
a r t i c l e i n f o
Article history:
Received 30 January 2006
Received in revised form
30 May 2006
Accepted 1 June 2006
Keywords:
Caries
Detection
QLF
ECM
Accuracy
Reliability
Sensitivity
Specificity
a b s t r a c t
Recent years have seen an increase in research activity surrounding diagnostic methods,
particularly in the assessment of early caries lesions. The drive for this has come from two
disparate directions. The first is from the dentifrice industry who are keen to develop
techniques that would permit caries clinical trials (CCTs) to be reduced in duration and
subject numbers to permit the investigation of novel new anti-caries actives. The second is
from clinicians who, armed with the therapies to remineralise early lesions are now seeking
methods to reliably detect such demineralised areas and implement true preventative
dentistry. This review examines novel technologies and the research supporting their
use. Techniques based on visual, optical, radiographic and some emerging technologies
are discussed. Each have their benefits although systems based on the auto-fluorescence
(such as QLF) of teeth and electrical resistance (such as ECM) seem to offer the most hope for
achieving reliable, accurate detection of the earliest stages of enamel demineralisation.
# 2006 Elsevier Ltd. All rights reserved.
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1. Introduction
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.1
All of these interactions are taking place in the complex
biofilm overlaying the tooth surface which comprises of the
pellicle as well as the oral microflora of the plaque.2 The
modifiers of this system are well known and are summarised
in Table 1 with Fig. 1 presenting an overview of the dynamics
of the caries process.2 With this greater understanding of the
disease, comes an opportunity to promote ‘preventative’
therapies that encourage the remineralisation of non-cavi-
* Tel.: +44 161 226 1211; fax: +44 161 232 4700.E-mail address: [email protected].
0300-5712/$ – see front matter # 2006 Elsevier Ltd. All rights reserveddoi:10.1016/j.jdent.2006.06.001
tated 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.3,4 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 currently available to
practitioners or will shortly be made so.
It is a crucial distinction that the systems described within
this review are correctly classified as caries detection systems,
rather than diagnostic systems. Diagnosis is a decision process
that rests with the clinician and is informed by, initially,
detection of a lesion and should be followed by an assessment
.
j o u r n a l o f d e n t i s t r y 3 4 ( 2 0 0 6 ) 7 2 7 – 7 3 9728
Table 1 – Risk and modifying factors for caries
Primary risk factors
Saliva
(1) Ability of minor salivary glands to produce saliva
(2) Consistency of unstimulated (resting) saliva
(3) pH of unstimulated saliva
(4) Stimulated salivary flow rate
(5) Buffering capacity of stimulated saliva
Diet
(6) Number of sugar exposures per day
(7) Number of acid exposures per day
Fluoride
(8) Past and current exposure
Oral biofilm
(9) Differential staining
(10) Composition
(11) Activity
Modifying factors
(12) Past and current dental status
(13) Past and current medical status
(14) Compliance with oral hygiene and dietary advice
(15) Lifestyle
(16) Socioeconomic status
of the patient’s caries risk which may include the number of
new caries lesions, past caries experience, diet, presence or
absence of favourable or unfavourable modifying factors
(salivary flow, mutans streptococci counts, oral hygiene) and
qualitative aspects of the disease such as colour and
anatomical location.5 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.6 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.
Pitts provides a useful visual description of the benefits of
early caries detection.7 Using the metaphor of an iceberg, it
Fig. 1 – Demineralisation and remineralisation cycle for
can be seen that traditional methods of caries detection result
in a vast quantity of undetected lesions. There is a clinical
argument about the significance of these lesions, with some
authors believing that only a small percentage will progress to
more severe disease, however, it is a undisputed fact that all
cavitated lesions with extension in pulp began their natural
history as an early lesion. Fig. 2 demonstrates the Pitts iceberg.
From this it can be seen that as the sensitivity of the detection
device increases, so does the number of lesions detected. It can
also be seen that the new detection tools are required to
identify those lesions that would be amenable to remineralis-
ing therapies.8
When assessing the effectiveness of such methods, the
preferred reporting metrics are those of traditional diagnostic
science; namely specificity, sensitivity, area under the ROC
curve and the correlation with the truth (the true state of the
disease, established using a gold standard). The reliability or
reproducibility of the test can be established using either
intra-class correlation or kappa coefficients depending on the
nature of the metric output, i.e. either continuous or
ordinal.9,10
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 rough-
ness.11 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.11
It is worthwhile to take an overview of the performance of
the traditional caries detection systems and these are shown,
in terms of sensitivity and specificity in Figs. 3 and 4. Fig. 3
demonstrates the methods’ performance irrespective of the
severity of the lesion, with Fig. 4 presenting the same data for
lesions confined to enamel. These data are based on the
excellent systematic review by Bader et al.12 who restricted his
assessment of studies to those that employed histological
validation. This therefore indicates that while the ‘true’
diagnostic outcome is not in doubt, these studies were
conducted in vitro and hence the actual values in clinical
enamel caries (adapted from Mount and Hume56).
j o u r n a l o f d e n t i s t r y 3 4 ( 2 0 0 6 ) 7 2 7 – 7 3 9 729
Fig. 2 – The ‘iceberg’ of caries and the influence of detection system (modified from Pitts, 20017).
Table 2 – Methods of caries detection based on theirunderlying physical principles
Physical principle Application in caries detection
X-rays Digital subtraction radiography
Digital image enhancement
Visible light Fibre optic transillumination (FOTI)
Quantitative light-induced fluorescence
(QLF)
Digital image fibre optic transillumination
(DiFOTI)
Laser light Laser fluorescence measurement
(DiagnoDent)
Electrical current Electrical conductance measurement (ECM)
Electrical impedance measurement
Ultrasound Ultrasonic caries detector
Modified from literature.51
practice are likely to be poorer. A scant assessment of the
figures indicates that while specificity is adequate, the
sensitivity scores of the traditional methods are poor, with
many being significantly less than chance; i.e. a guess would
Fig. 3 – Effectiveness of traditional caries detection systems
based on lesions of any severity, after Bader et al.12
provide the same or a better result in many cases. These
figures serve to illustrate the need for detection devices that
are objective, quantitative, sensitive and enable early lesions
to be monitored over time. This longitudinal monitoring is
especially important when one considers the treatment of
early caries lesions.
The following review describes those systems that have
potential to meet the aims of clinicians and researchers for
enhanced sensitivity and objective, metric, continuous mea-
sures of mineralisation status.
2. Detection systems based on electricalcurrent 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 will have an effect on this
conductance.11 Biological materials are no exception and the
concentration of fluids and electrolytes contained within such
Fig. 4 – Effectiveness of traditional caries detection systems
based on lesions restricted to enamel only, after Bader
et al.12
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materials largely govern their conductivity.13 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.14
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.
Fig. 6 – A demonstration of an ECM profile obtained from a
primary root caries lesion in vitro demonstrating the sites
assessed.
3. Electronic caries monitor (ECM)
The ECM device employs a single, fixed-frequency alternating
current which attempts to measure the ‘bulk resistance’ of
tooth tissue15 (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 cycle, compressed air is expressed from
the tip of the probe and this 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. 6. While it is generally
accepted that the increase in porosity associated with caries is
responsible for the mechanism of action for ECM,15 there are
some points to consider:
(1) D
Fig
me
o electrical measurements of carious lesions measure the
volume of the pores, and if so, is it the total pore volume or
. 5 – The ECM device (Version 4) and its clinical application. (a) T
asurement technique, (d) surface specific measurement techniq
just a portion, perhaps the superficial portion, that is
measured?
(2) D
o electrical measurements measure pore depth? If this isthe case, what happens during remineralisation where the
superficial layer may remineralise, leaving a pore beneath?
(3) I
s the morphological complexity of the pores a factor in themeasurement 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,16 the thickness of the tissue,17 the hydration of the
he ECM machine, (b) the ECM handpiece, (c) site specific
ue.
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Table 3 – ECM ROC areas under the curve
ROC–area Diagnostic threshold Tooth type Surface or site specific measurement Study
0.82 D1 Premolars Site specific 52
0.80 D1 Molars Site specific 53
0.84 D3 Premolars Site specific 52
0.82 D3 Molars Site specific 54
0.80 D1 Premolars Surface specific 19
0.67 D1 Premolars Surface specific 19
0.94 D3 Premolars Surface specific 19
0.79 D3 Molars Surface specific 55
Fig. 7 – 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.
material (i.e. one should not dry the teeth prior to use) and the
surface area.15
An excellent review of the performance of ECM was
undertaken in 2000 by Huysmans18 who collated information
from a variety of validation studies. She was unable to perform
a meta-analysis of these data; stating that aspects of the
studies such as version of equipment, storage medium, cut-
offs and tooth type prevented direct comparisons. A summary
of her findings are presented in Table 3, these demonstrate a
good to excellent range of area under the curves (AUC’s) with
the exception of surface specific premolars when assessing at
the D1 level (lesions restricted to enamel). The sensitivity and
specificity values were assessed from a number of studies; for
site specific measurements these were; sensitivity 74.8(� 11.9)
and specificity 87.6(� 10) and for surface specific measure-
ments; 63(� 2.8) and 79.5(� 9.2). The lower efficacy in surface
specific measurements has led to this area of research being
neglected, with the vast majority of publications concentrat-
ing on site specific measurements.
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. The intra-class
correlation coefficients for site specific were 0.76 and 0.93 for
surface specific.19 It is important to note that these high figures
relate to the use of the device in a controlled, laboratory
setting. Further studies in vitro are required before the device
can be used for monitoring lesions longitudinally. For
example, some authors have stated that the limits of
agreement can be as much as �580 kV for surface specific
measurements. If the range for an occlusal surface is
considered as 100–5000 kV then this could be a substantial
source of error.20
A clinical trial has been undertaken using the ECM device
on root caries, 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 cap-
ability than the lower fluoride paste users21 (see Fig. 7). 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.21
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 capaci-
tance and impendence among others.22 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. A prototype has been developed and is being
commercially exploited and a market release is expected in
2006.15
4. Radiographic techniques
4.1. Digital radiographs
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 conven-
tional 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.23
However, digital radiographs offer the potential of image
j o u r n a l o f d e n t i s t r y 3 4 ( 2 0 0 6 ) 7 2 7 – 7 3 9732
Fig. 8 – 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.
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 perfor-
mance is at least as good as conventional radiographs,24 with
reported values of 0.95 (sensitivity) and 0.83 (specificity) for
approximal lesions. See Fig. 8 for an example of this
enhancement. When these findings are considered, one must
remember that digital radiographs offer a decrease in radio-
graphic dose and thus offer additional benefits than diagnostic
yield. Digital images can also be archived and replicated with
ease.
4.2. Subtraction radiology
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.25 The
basic premise of subtraction radiology is that two radiographs
of the same object can be compared using their pixel values. If
Fig. 9 – Example of a subtraction of two digital bitewing radiog
surface of first molar, (b) follow up radiograph taken 12 months
shown as black, i.e. in this case the proximal lesion has becom
the images have been 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.26 The value of the pixels from the first object are
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 deminer-
alisation, or regression. Subtraction images therefore empha-
sise 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 repre-
sented as change.27 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.27 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. 9.
raphs. (a) Radiograph showing proximal lesion on mesial
later, (c) the areas of difference between the two films are
e more radiolucent and hence has progressed.
j o u r n a l o f d e n t i s t r y 3 4 ( 2 0 0 6 ) 7 2 7 – 7 3 9 733
Fig. 10 – Example of early lesions before (a) and after (b)
drying.
Fig. 11 – FOTI equipment.
5. Enhanced visual techniques
5.1. Fibre optic transillumination (FOTI and DiFOTI)
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,
Fig. 12 – Example of FOTI on a tooth. (a)
visible light, this appears as a ‘whiter’ area—the so called
white spot.28 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 teeth29 (see Fig. 10).
Fibre optic transillumination takes advantage of these
optical properties of enamel and enhances them by using a
high intensity white light that is presented through a small
aperture in the form of a dental handpiece. 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. 11). 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 lesions. The research around
FOTI is somewhat polarised, with a recent review finding a
mean sensitivity of only 14 and a specificity of 95 when
considering occlusal dentine lesions, and 4 and 100% for
Normal clinical vision, (b) with FOTI.
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proximal lesions.30 This is in contrast to other studies where
sensitivity was recorded at 85% and specificity at 99%.31 Many
of the differences can be explained by the nature of the ordinal
scale used to record the subjective visual assessment and the
gold standard used to validate the method. However, one
would expect FOTI to be at least as effective as a visual
examination.
Recent developments in ordinal scales for visual assess-
ments, such as the ICDAS scoring system,32 may enable a more
robust framework for visual exams into which FOTI can be
added (Fig. 12). One would expect that FOTI would enable
discrimination of occlusal lesions to be improved (particularly
dentine lesions), as well as detection of proximal lesions (in
the absence of radiographs) to be higher.29 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. Indeed, some work has been
undertaken trialling the use of FOTI in practice with
encouraging results.33
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. Longitudinal
monitoring is, therefore, a complex matter and some degree of
training is required in order to be competent at this level of
FOTI usage. In order to address some of these concerns, an
imaging version of FOTI has been developed; digital imaging
FOIT (DiFOTI). This system comprises of a high intensity light
and grey scale camera which can be fitted with one of two
heads; one for smooth and one for occlusal surfaces. Images
are displayed on a computer monitor and can be archived for
retrieval at a repeat visit. However, there is no attempt within
the software to quantify the images, and analysis is still
undertaken visually by the examiner who makes a subjective
call based on the appearance of scattering.34
Fig. 13 – 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.
6. Fluorescent techniques
6.1. 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 bandpass filter at
l > 540 nm by a small intra-oral camera. This produces an
image that is comprised of only green and red channels (the
blue having been filtered out) and the predominate colour of
the enamel is green.35,36 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; r = 0.73–0.86.37
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.37 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.
The QLF equipment is comprised of a light box containing a
xenon bulb and a handpiece, similar in appearance to an intra-
oral camera, see Fig. 13. Light is passed to the handpiece via a
liquid light guide and the handpiece contains the bandpass
filter.38 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 image all tooth surfaces except inter-
j o u r n a l o f d e n t i s t r y 3 4 ( 2 0 0 6 ) 7 2 7 – 7 3 9 735
Fig. 14 – 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.
proximally. See Fig. 14 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 assess-
ment 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. 15 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. For
occlusal caries sensitivity has been reported at 0.68 and
specificity at 0.70, and this compares well with other systems.
Correlations of up to 0.82 have also been reported for QLF
metrics and lesion depth. Smooth surfaces, secondary caries
and demineralisation adjacent to orthodontic brackets have all
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. Intraclass correlation
coefficients have been reported as 0.96 for image capture, with
analysis at 0.93 for intra-examiner and 0.92 for inter-examiner
comparisons. Again, these compare well to other systems.
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. 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 fluorescence, and whether
or not this can be a predictor of lesion activity and again,
research is currently being undertaken in this area.
6.2. 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 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 (Figs. 15 and 16).
Initial evaluations of the device suggest that it may be a
promising tool for clinical use; correlation with histological
depth of lesions was substantial at 0.85 and the sensitivity and
specificity for dentinal lesions were 0.75 and 0.96, respec-
tively.39 Reliability of the device measured by Kappa was 0.88–
0.90 for intra-examiner and 0.65–0.73 for inter-examiner.40
Further in vitro studies have found that the area under the
ROC was significantly higher for DD (0.96) than that for
conventional radiographs (0.66).41 However, the device is not
j o u r n a l o f d e n t i s t r y 3 4 ( 2 0 0 6 ) 7 2 7 – 7 3 9736
Fig. 15 – 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.
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.39 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.42 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
Fig. 16 – The DIAGNODent device.
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.42 It 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.
6.3. Other optical techniques
There are a number of other techniques for detecting caries
using optical methods. These systems are in their infancy and
many are based solely in laboratories. However, such
technologies may prove useful in the future. Examples include
optical coherence tomography (OCT), and near infra-red
imaging. OCT has been shown to be able to image early
enamel caries lesions in extracted teeth,43 and also on root
lesions.44 Like many other novel techniques, it is likely that
stain will adversely effect OCT.45 Work has just begun on using
near infra-red, but initial results look promising.46 There is
significant work involved in developing these systems into
clinically and commercially acceptable applications and so it
could be some time until these new methodologies can be
properly assessed in clinical trials.
6.4. Ultrasound techniques
The use of ultrasound in caries detection was first suggested
over 30 years ago, although developments in this field have
been slow. The principle behind the technique is that sound
j o u r n a l o f d e n t i s t r y 3 4 ( 2 0 0 6 ) 7 2 7 – 7 3 9 737
waves can pass through gases, liquids and solids and the
boundaries between them.45 Images of tissues can be acquired
by collecting the reflected sound waves. In order for sound
waves to reach the tooth they must pass first through a
coupling mechanism, and a number of these have been
suggested, but those with clinical applications include water
and glycerine.45 A number of studies have been undertaken
using ultrasound, with differing levels of success. One study
reported that an ultrasound device could discriminate
between cavitated and non-cavitated inter-proximal lesions47
in vitro. A further study found that ultrasonic measurements
at 70 approximal sites in vitro resulted in a sensitivity of 1.0
and a specificity of 0.92 when compared to a histological gold
standard.48 Further histological validation has been under-
taken by using transverse microradiography and ultrasound.49
A final in vivo study was undertaken using a device described
as the Ultrasonic Caries Detector (UCD) which examined 253
approximal sites and claimed a diagnostic improvement over
bitewing radiography.50 Despite these encouraging findings,
no further research has been undertaken using the device and
the research has only been published as abstracts.
7. Conclusion
A range of caries detection systems have been covered in this
review. A summary of their performance is presented in Fig. 17.
The pattern of dental caries is changing, with an increasing
incidence in occlusal surfaces. This shift has rendered tradi-
tional detection systems, particularly bitewing radiographs less
useful in the diagnostic protocols of clinicians. High concentra-
tion fluoride varnishes have been demonstrated to arrest the
progression of early lesions, but often traditional methods of
detection are too insensitive to permit the most efficacious use
of these products. Caries clinical trials involving thousands of
subjects over several years employ are no longer commercially
viable. For all of these reasons, there is a real need for a range of
caries detection and quantification systems to augment the
clinician’s diagnostic pathway.
Fig. 17 – A summary of the diagnostic performance (validity
and reliability) of a range of novel caries detection systems
based on D3 lesions, in vitro, on occlusal surfaces, after
Pretty57
The evidence supporting each of the systems is currently
limited; often by virtue of the in vitro nature of the studies, or
due to a failure of standardisation of approach to study design
making meta-analyses impossible. However, if we can state
with some confidence that the systems do permit earlier
detection of enamel lesions, and systems such as QLF and
DiFOTI enable images of these lesions to be stored and viewed
at a later date. It is worthwhile considering what the purpose
may be for supplementing or even replacing well established
dental diagnostic systems; they must offer improved diag-
nostic efficiency, better patient care pathways or perhaps
comply with legislative changes. There is a paradigm shifty
occurring in dentistry; we are slowly moving away from a
surgical model into one more medically based. The devices
described within this paper, by enabling early detection of
caries enable the remineralising therapies to be correctly
prescribed and for their success to be measured.
The advent of dental auxiliaries who can undertake an
increasing number of procedures emphasises the important
role that the dentist plays as the leader of the dental team. This
leadership role is critically tied to the fact that dental clinicians
retain the sole right of diagnosis and thus the devices and
approaches described within the current paper serve only to
augment the diagnostic skills of the clinician. Making the right
decision about the presence or absence of a lesion, its degree of
severity and its likely activity combined with the socio-
behavioural aspects of the patient, their risk and modifying
factors will continue to rest with the dentist.
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