Establishing Relationship for Caries Assessment using Micro-Computed Tomography and Diagnodent

Objectives: Diagnodent^TM is an established method for clinical assessment of caries; however, it does not give the actual value for the mineral density of the tooth tissue. Establishing a relationship between Diagnodent measurement and that of a device which can measure the mineral density of the caries lesion, would facilitate monitoring of the mineral status of a caries lesion and/or the effect of an applied therapeutic agent. Micro-Computed Tomography (MicroCT^TM) is currently used in the laboratory to non-invasively quantify the mineral density of calcified tissues. It measures the linear attenuation coefficient of the tissue and relates it directly to its mineral density. This study aimed to establish a mathematical equation relating MicroCT (µCT) and Diagnodent (Dd), for use in evaluating the mineral status of a caries lesion by a combined use of the two systems. Methods: Using MicroCT and Diagnodent, the baseline measurements were taken on defined spots on the enamel surface of twenty extracted human teeth and the data recorded. Caries-like lesions were created on those spots by 3-day demineralization in acidified gel system. The spots (lesions) were then re-assessed with the two systems. Results: In either systems, paired t-tests (a=0.05) indicated a significant difference between the pre- and post-demineralization data (n=20, p<0.001). Using Linear Regression coefficient and squared Pearson correlation coefficient (r²), a linear correlation (regression equation: µCT = 0.82 + 0.57Dd; r² =0.36) was observed between the measurements of MicroCT (range 3.73 – 6.0 cm^-1) and that of Diagnodent (range 4 – 9) for the post-demineralization (caries lesion) measurements. Conclusions: We conclude that the equation established in this study can be used to extrapolate the mineral density in a caries lesion detected and measured using Diagnodent, and may be useful for monitoring the progress of an early caries being treated with a therapeutic agent such as fluoride.