Dental imaging methods for the detection of early tooth decay

Why is it important to improve the detection of dental caries (tooth decay)?
Dentists often aim to identify tooth decay that has already advanced to a level which needs a filling. If dentists were able to find tooth decay when it has only affected the outer layer of the tooth (enamel) then it is possible to stop the decay from spreading any further and prevent the need for fillings. It is also important to avoid a false-positive result, when treatment may be given when caries is absent.

What is the aim of this review?
This Cochrane Review aimed to find out how accurate X-ray images and other types of dental imaging are for detecting early tooth decay as part of the dental 'check-up' for children and adults who visit their general dentist. Researchers in Cochrane included 77 studies published between 1986 and 2018 to answer this question.

What was studied in the review?
Three main types of dental imaging were studied in this review: analogue or digital radiographs (X-rays) and three-dimensional (3D) imaging (cone beam computed tomography (CBCT)). We studied decay on the occlusal surfaces (biting surfaces of the back teeth), the proximal surfaces (tooth surfaces that are next to each other), and smooth surfaces.

What are the main results of the review?
Researchers in Cochrane included 77 studies with a total of 15,518 tooth sites or surfaces, where typically 63% of tooth sites or surfaces had enamel caries. Some of these studies reported on more than one type of imaging, on both the permanent and primary ('milk') teeth or different tooth surfaces, and this gave us 104 sets of data to use. If these methods were to be used by a dentist for a routine dental examination, out of 1000 tooth sites or surfaces seen:
• the use of these methods will indicate that 336 tooth sites or surfaces will have early tooth decay, and of these, 43 (13%) will have no disease (incorrect diagnosis - false positive);
• of the 664 tooth sites with a result indicating that early tooth decay is absent, 337 (51%) will have early tooth decay (incorrect diagnosis - false negative).
This high proportion of false-negative results means that early signs of decay will be missed. We found evidence that 3D imaging methods were better than analogue or digital radiographs at identifying early disease but that analogue radiographs were better at identifying disease-free tooth surfaces.

Please see oralhealth.cochrane.org/imaging-modalities-inform-detection-and-diagnosis-early-caries.

How reliable are the results of the studies in this review?
We only included studies that assessed healthy teeth or those that were thought to have early tooth decay. This is because teeth with deep tooth decay would be easier to identify. However, there were some problems with how the studies were conducted. This may result in these methods appearing more accurate than they are, increasing the number of correct results. We judged the certainty of the evidence to be low due to how the studies selected their participants and the large number of studies that were carried out in a laboratory setting on extracted teeth, and the variation in the results.

Who do the results of this review apply to?
Studies included in the review were carried out in South America, Europe, Asia, and the US. A large number of studies examined extracted teeth, while clinical studies were completed in dental hospitals or general dental practices.

What are the implications of this review?
Low-certainty evidence suggests that imaging for the detection or diagnosis of early tooth decay may result in a relatively high proportion of false-negative results, with the potential for early disease to become more advanced. If left untreated, the opportunity to provide professional or self-care practices to arrest or reverse early tooth decay will be missed.

How up-to-date is this review?
The electronic searches retrieved used studies published up to 31 December 2018.

Authors' conclusions: 

The design and conduct of studies to determine the diagnostic accuracy of methods to detect and diagnose caries in situ are particularly challenging. Low-certainty evidence suggests that imaging for the detection or diagnosis of early caries may have poor sensitivity but acceptable specificity, resulting in a relatively high number of false-negative results with the potential for early disease to progress. If left untreated, the opportunity to provide professional or self-care practices to arrest or reverse early caries lesions will be missed. The specificity of lesion detection is however relatively high, and one could argue that initiation of non-invasive management (such as the use of topical fluoride), is probably of low risk.

CBCT showed superior sensitivity to analogue or digital radiographs but has very limited applicability to the general dental practitioner. However, given the high-radiation dose, and potential for caries-like artefacts from existing restorations, its use cannot be justified in routine caries detection. Nonetheless, if early incidental carious lesions are detected in CBCT scans taken for other purposes, these should be reported. CBCT has the potential to be used as a reference standard in diagnostic studies of this type.

Despite the robust methodology applied in this comprehensive review, the results should be interpreted with some caution due to shortcomings in the design and execution of many of the included studies. Future research should evaluate the comparative accuracy of different methods, be undertaken in a clinical setting, and focus on minimising bias arising from the use of imperfect reference standards in clinical studies.

Read the full abstract...
Background: 

The detection and diagnosis of caries at the earliest opportunity is fundamental to the preservation of tooth tissue and maintenance of oral health. Radiographs have traditionally been used to supplement the conventional visual-tactile clinical examination. Accurate, timely detection and diagnosis of early signs of disease could afford patients the opportunity of less invasive treatment with less destruction of tooth tissue, reduce the need for treatment with aerosol-generating procedures, and potentially result in a reduced cost of care to the patient and to healthcare services.

Objectives: 

To determine the diagnostic accuracy of different dental imaging methods to inform the detection and diagnosis of non-cavitated enamel only coronal dental caries.

Search strategy: 

Cochrane Oral Health's Information Specialist undertook a search of the following databases: MEDLINE Ovid (1946 to 31 December 2018); Embase Ovid (1980 to 31 December 2018); US National Institutes of Health Ongoing Trials Register (ClinicalTrials.gov, to 31 December 2018); and the World Health Organization International Clinical Trials Registry Platform (to 31 December 2018). We studied reference lists as well as published systematic review articles.

Selection criteria: 

We included diagnostic accuracy study designs that compared a dental imaging method with a reference standard (histology, excavation, enhanced visual examination), studies that evaluated the diagnostic accuracy of single index tests, and studies that directly compared two or more index tests. Studies reporting at both the patient or tooth surface level were included. In vitro and in vivo studies were eligible for inclusion. Studies that explicitly recruited participants with more advanced lesions that were obviously into dentine or frankly cavitated were excluded. We also excluded studies that artificially created carious lesions and those that used an index test during the excavation of dental caries to ascertain the optimum depth of excavation.

Data collection and analysis: 

Two review authors extracted data independently and in duplicate using a standardised data extraction form and quality assessment based on QUADAS-2 specific to the clinical context. Estimates of diagnostic accuracy were determined using the bivariate hierarchical method to produce summary points of sensitivity and specificity with 95% confidence regions. Comparative accuracy of different radiograph methods was conducted based on indirect and direct comparisons between methods. Potential sources of heterogeneity were pre-specified and explored visually and more formally through meta-regression.

Main results: 

We included 104 datasets from 77 studies reporting a total of 15,518 tooth sites or surfaces. The most frequently reported imaging methods were analogue radiographs (55 datasets from 51 studies) and digital radiographs (42 datasets from 40 studies) followed by cone beam computed tomography (CBCT) (7 datasets from 7 studies). Only 17 studies were of an in vivo study design, carried out in a clinical setting. No studies were considered to be at low risk of bias across all four domains but 16 studies were judged to have low concern for applicability across all domains. The patient selection domain had the largest number of studies judged to be at high risk of bias (43 studies); the index test, reference standard, and flow and timing domains were judged to be at high risk of bias in 30, 12, and 7 studies respectively.

Studies were synthesised using a hierarchical bivariate method for meta-analysis. There was substantial variability in the results of the individual studies, with sensitivities that ranged from 0 to 0.96 and specificities from 0 to 1.00. For all imaging methods the estimated summary sensitivity and specificity point was 0.47 (95% confidence interval (CI) 0.40 to 0.53) and 0.88 (95% CI 0.84 to 0.92), respectively. In a cohort of 1000 tooth surfaces with a prevalence of enamel caries of 63%, this would result in 337 tooth surfaces being classified as disease free when enamel caries was truly present (false negatives), and 43 tooth surfaces being classified as diseased in the absence of enamel caries (false positives). Meta-regression indicated that measures of accuracy differed according to the imaging method (Chi2(4) = 32.44, P < 0.001), with the highest sensitivity observed for CBCT, and the highest specificity observed for analogue radiographs. None of the specified potential sources of heterogeneity were able to explain the variability in results. No studies included restored teeth in their sample or reported the inclusion of sealants.

We rated the certainty of the evidence as low for sensitivity and specificity and downgraded two levels in total for risk of bias due to limitations in the design and conduct of the included studies, indirectness arising from the in vitro studies, and the observed inconsistency of the results.

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