An X-Ray Microtomography Study on the Mineral Concentration of Carious Dentine Removed during Cavity Preparation in Deciduous Molars

Dentists use a number of criteria in order to assess when a cavity is caries free, amongst which hardness is probably the most widely used. However, the judgement is subjective. X-ray microtomography (XMT) is a non-destructive microscopic technique that allows in vitro specimens to be scanned, manipulated and then rescanned. In this study, a high-definition XMT scanner was used to determine the mineral distribution of carious dentine in 10 deciduous molars, and the extent of dentine removed by an experienced clinician was investigated. For each tooth, after an initial XMT scan, caries was removed using a steel bur in a slow hand-piece. The tooth was then repositioned and rescanned. Mineral concentrations were calculated from the linear attenuation coefficients assuming the mineral phase to be hydroxyapatite and the organic phase to be collagen. The volume of dentine tissues removed was calculated by subtracting data of the second scan from the first. The results showed that the mean modal mineral concentration for the 10 teeth was 1.42 g · cm –3 for sound dentine. Because of uncertainty about collagen concentration in carious dentine, the mean modal mineral concentration for the carious dentine had a range of 0.37–0.5 g · cm –3 . It was found that the subjective criteria used by the operator could lead to inconsistency of cavity preparation. The cavities could be overprepared by 8.5–44.3% in volume. However, the overpreparation was not uniform throughout the cavity: residual demineralised dentine could still be detected in the postoperative scan in isolated regions.