X-ray microtomography study of carious dentine and a comparison of its removal by three techniques

Abstract

The wisdom on mechanical removal of carious dentine based on hardness has been challenged and chemo-mechanical technique has been proposed as a more conservative method. However, the extent and comparison of excessive removal of sound dentine and insufficient removal of carious dentine have not been studied. The aims of the present study are to use X-ray microtomography (XMT) to determine the mineral concentrations of sound and carious dentine, and the excavated dentine using a hand excavation (HE) technique, a hand excavation technique aided by Caries Detector Dye (CD) and a chemo-mechanical removal technique using Carisolv (CSS). Comparison of the three techniques with respect to the mineral concentrations of the excavated dentine caries and the volumes of sound dentine removed were investigated. It was aimed to identify the boundary between ―infected‖ and ―affected‖ using the X-ray linear attenuation coefficients (LAC) from the XMT results and the ultrastructural images obtained from the Back Scattered Electron (BSE) imaging and Atomic Force Microscopy (AFM). Thirty eight deciduous molars with open carious cavities were sectioned in half. One half of each molar had the carious tissue removed by HE and the other by CSS or hand excavation plus CD. XMT images were taken before and after caries removal. From the data set, an assessor, who was ‗blind‘ to which technique was used, used LAC histograms to assess the efficacy of the excavation techniques. The volumes of sound dentine removed by the 3 techniques were calculated and compared. Detailed analyses were carried out using XMT slices to investigate the mineral concentration of removed and residual dentine. Remineralisation experiments of residual dentine were performed 7 after caries removal. Backscattered electron (BSE) microscopy and atomic force microscopy (AFM) were used to investigate the ultrastructure of the carious dentine. The results showed that CSS was a better technique; conforming to the principles of minimally invasive dentistry. Volume analyses showed that both CSS and CD were effective in removing less sound dentine than conventional hand excavation. It was shown for the first time that the partially demineralised layer of dentine in a natural carious lesion, which was maintained by the CSS technique, had the potential to remineralise up to 80% of the mineral level for sound dentine. Combining XMT results with AFM and BSE images, ultrastructural changes were found at the boundary around a LAC value of 0.8 cm-1 which corresponded to a KHN of 7.66 kgmm-2. It was concluded that carious dentine removal up to a hardness level of 7.66 kgmm-2 could be recommended in order to preserve dentine that has potential to remineralise.