caries detection and diagnosis novel technologies

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

.

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http://dx.doi.org/10.1016/j.jdent.2006.06.001


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


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 is
the 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 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,16 the thickness of the tissue,17 the hydration of the

he ECM machine, (b) the ECM handpiece, (c) site specific

ue.


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



0.79 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


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.


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.


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-


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


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


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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