Promising imaging method for the early detection of dental caries

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detecting dental caries
a. Pseudocolor 3D OCT image of posterior teeth processed translucently. Presence of caries at the proximal surface was clearly imaged with the lesion location and size (white arrow). b1-5. Sequential 2D images acquired in 3D view from different thickness. White arrows: caries within the enamel. Red arrow: dentin caries. Blue arrow: slight change of enamel surface because of caries.

Japanese researchers have found that optical coherence tomography, an imaging method based on infrared radiation, can be used for detecting dental caries on the surface of rear teeth. As infrared light is non-ionising, the method is safer than radiography, which involves X-rays.

Dental caries affect more than 90 per cent of the world’s adult population. And often, dental caries are detected ‘too late’, requiring invasive teeth treatment. Visual examination (by a dentist) and radiography are currently the main tools for diagnosing caries. However, they are not completely efficient for detecting caries in posterior teeth—moreover, radiography is considered problematic for pregnant women and infants. 

A promising alternative technique, which is non-invasive and does not involve X-rays, is optical coherence tomography (OCT)—an imaging method that can be used to create a 3D representation of teeth. 

Now, a team from Okayama University have tested the accuracy of OCT for diagnosing caries in posterior teeth—publishing their findings in Scientific Reports. They found that the method could indeed become a viable alternative for radiography.

In OCT, a sample is irradiated with infrared light; different types of tissue scatter and absorb the infrared radiation differently. Scattering/absorption images (that are two-dimensional) obtained for many different irradiation angles can then be combined into a 3D visualisation of the sample. Because dental caries have a specific response to the radiation, they can be detected on the 3D image—in principle.

To check whether OCT is actually accurate enough for detecting caries in posterior teeth, the researchers compared radiography and OCT results for 51 proximal surfaces of 36 molars. 

The study was performed ex vivo: the molars were mounted in silicone blocks in a way corresponding to their normal anatomical position. The degree of caries present on the surface was marked histologically with a score from 0 to 5, corresponding to ‘sound tooth surface’ and ‘distinct cavity with visible dentin’, respectively. 

In order to make a quantitative comparison between radiography and OCT, certain parameters like sensitivity and specificity for the detection of caries were evaluated by 13 dentists. A statistical analysis then led to the conclusion that OCT appears to be a suitable method for diagnosing proximal enamel damage, and for following-up on whether non-invasive treatment—typically based on stopping and reversing the demineralisation of the enamel layer—is successful. 

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