Measurement of Caries Lesion by Microradiography and Micro-CT: A Correlation-Study

Method: Lesion-depth and mineral-loss of 13 natural enamel carious lesions were evaluated by both methods. In order to measure exactly the same slice in both methods, a special sample holder was prepared. A box of around the size of the enamel specimens prepared for the TMR-measurements was made with a diamond bur in slow rotation on the inside-upper part of a tooth (crown). This arrangement made it possible to include the slices into this tooth, for direct comparison of samples between the two methods. This was necessary in order not only to simulate a real situation, when the samples are non-destructively measured as a whole tooth, but also to respect the signal-to-noise ratio. Samples were scanned with a small-angle-cone-beam microCT (μCT 40; Scanco MedicalAG, Switzerland) at 70kVp and 114μA, at a linear resolution of 8μm. Transverse microradiographs of the enamel specimens were obtained with a nickel-filtered copper(CuKa) X-ray source(PW 1830/40; Philips, Kassel, Germany) operating at 20kV and 20mA with a focus-specimen distance of 34cm. From the tooth slice, together with an aluminum calibration step wedge, an x-ray projection of the microradiogram is made on highresolution photographic film (high-speed holographic film, Kodak SO-253, Germany). Start of lesion was defined as 20vol% for both methods. Dedicated software (TMR 2000, Version 2.0.27.11; Inspektor Research Systems BV, The Netherlands) was used to calculate the mineral content and depth profiles.

Result: A strong Pearson correlation was found between micro-CT and TMR measurements: 0.928 for mineral-loss and 0.854 for lesion-depth.

Conclusion: Micro-CT can be used to measure mineral profiles through natural enamel carious lesions.