Elsevier

Journal of Dentistry

Volume 34, Issue 10, November 2006, Pages 727-739
Journal of Dentistry

Review
Caries detection and diagnosis: Novel technologies

https://doi.org/10.1016/j.jdent.2006.06.001Get rights and content

Abstract

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.

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-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.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 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 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 remineralising 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 roughness.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 Fig. 3, Fig. 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 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 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 measures of mineralisation status.

Section snippets

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 will have an effect on this conductance.11 Biological materials are no exception and the concentration of fluids and electrolytes contained within such materials largely govern their conductivity.13 For

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

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

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

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

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 traditional detection systems, particularly bitewing radiographs less useful in the diagnostic protocols of clinicians. High concentration fluoride varnishes have been demonstrated to arrest the progression of early lesions, but often traditional methods

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