Almost since the discovery of x-rays by Roentgen in 1895, radiography has been used to detect the effects of dental caries on dental hard tissues. It has been primarily applied for the detection of lesions on the proximal surfaces of teeth that are not clinically visible for inspection. Occlusal caries may also be detected once it has progressed into the dentin.
Radiographic diagnosis of dental caries is based on the fact that as the caries process proceeds, the mineral content of enamel and dentin decreases, with a resultant decrease in the attenuation of the x-ray beam as it passes through the teeth. This process is recorded on the image receptor as an increase in radiographic density that must be detected by the clinician as a sign of a carious lesion. Many different factors can affect accurate detection of these lesions, such as exposure parameters, type of image receptor, image processing, display system, viewing conditions, and ultimately the training and experience of the human observer.
A systematic review of the existing literature was performed to address the question of the validity of six different diagnostic methods for the detection of dental caries in primary and permanent teeth. The diagnostic methods assessed included visual inspection, visual/tactile inspection, radiography, fiber-optic transillumination (FOTI), electrical conductance (EC), laser fluorescence (LF), and combinations of these methods.
Three primary computer indexes were used in searching the literature�MEDLINE, EMBASE, and the Cochrane controlled trials register. The period searched was from 1966 to December, 1999. Inclusion and exclusion criteria were clearly defined prior to performing the search. Studies were limited to those with human subjects and natural carious lesions, publication language in English, histological validation of caries status for each surface studied or visual/tactile validation of intact surface for cavitation only, outcomes expressed as sensitivity and specificity, or data provided from which these outcomes could be derived. While both in vitro and in vivo studies were included in the review, only those methods that are commercially available to the general practitioner were assessed.
Thirty-nine studies were selected from among 1,407 diagnostic reports that satisfied all criteria. These studies reported 126 different assessments of different diagnostic methods. Of these studies, 51 percent evaluated the diagnostic performance of radiographic methods. The studies were critically reviewed and a quality rating scale appraised several elements of internal validity, including study design, duration, sample size, blinding of examiners, baseline assessments, and examiner reliability. The overall strength of evidence supporting the validity of a method was judged in terms of the extent to which it offered unambiguous assessment of a particular method for identifying a specific type of lesion on a specific type of surface.
Systematic review of the dental literature indicates that the strength of evidence for radiographic methods for the detection of dental caries is poor for all types of lesions on posterior and occlusal surfaces. This is primarily due to the large amount of variation in the reported sensitivity and specificity of this method. Little, if any, evidence exists to support the use of radiographic methods for primary teeth, anterior teeth, or root surfaces. The literature is severely limited by problems associated with both internal and external validity. These include incomplete descriptions of sample selection, diagnostic criteria, and examiner reliability; the use of small numbers of examiners; nonrepresentative teeth samples with high lesion prevalence; and the use of reference standards of questionable reliability.
Although the strength of evidence is considered poor, this does not mean that the accuracy of radiographic methods is of no diagnostic value. It simply means that using the criteria established to evaluate the existing evidence, the evidence is inadequate to validate the method. Better studies designed to address the limitations of the current literature could in fact indicate that the method is valid, but the literature does call into question the relative importance of this method in making treatment decisions.
The evidence suggests that radiographic methods have a higher degree of specificity than sensitivity, which means that false negative diagnoses are proportionally more apt to occur in the presence of disease than are false positive diagnoses in the absence of disease. This outcome may be beneficial if the negative consequences of a false positive diagnosis outweigh those of a false negative diagnosis. If the only type of intervention is surgical removal of the lesion, a false positive results in a perfectly normal tooth being irreversibly damaged. A false negative results in further progression of the lesion and potentially further loss of tooth tissue. This outcome is somewhat abated by the fact that the lesion may be detected at a later time.
Nonsurgical interventions are gaining in popularity as alternatives to mechanical replacement of damaged tooth tissue with artificial materials. These nonsurgical methods are only effective if the lesion is detected prior to cavitation. This means that the lesion must be detected early. To detect the lesion earlier a diagnostic method must provide higher sensitivity, which may result in more false positive diagnoses. If early intervention consists of nonsurgical management that does not result in any permanent damage to the tooth, the negative consequences of a false negative diagnosis outweigh those of a false positive diagnosis.
New digital radiographic techniques which eliminate the use of silver halide emulsion x-ray film by capturing radiographic images on photo-stimulable phosphor imaging plates or charge-coupled devices may improve detection of dental caries. The images acquired with these technologies are digital and can be processed or analyzed to enhance diagnostic performance. The weight of available evidence suggests that the use of some digital methods offers some small gains in sensitivity without reduction in specificity, and that image analysis techniques may offer more substantial gains.
Renewed effort should be made to ensure that future studies address the question of diagnostic validity adequately. Guidelines should be developed for assessing diagnostic methods which assist researchers in developing study designs that will hold up to critical review.
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