Micro-computed tomography in caries research

Over the past years there have been attempts to improve the development of techniques for caries detection and quantification. The demand for a non-destructive method has encouraged the use of micro-CT in studies of enamel de-remineralization. Our contribution to this development were presented in this work by evaluating the limitations of the method concerning energy and the size of the samples, by correlating the micro-CT results of mineral loss and lesion depth with a gold standard (TMR), and by suggesting a three-dimensional model for the study of dentin caries excavation methods. After a literature review, which is the content of the first and second chapter of this work, we evaluated a second generation fan-beam commercial micro-CT (μCT 20, SCANCO Medical AG, Bassersdorf, Switzerland) for mineral content quantification. According to our results, the machine that works at 50 kVp and 160 μA is not feasible to quantify the mineral content of whole tooth. Thus, we strongly recommended to consider the limited acceleration voltage of the μCT 20 system and to limit sample evaluation to 6-mm thickness which is already an advantage over other analytic approaches which require the preparation of very thin, micrometric-sized samples. The correlation of micro-CT and TMR was evaluated in our second experiment, written in chapter 5. After exposing 70-90 μm slices with natural carious lesion in enamel by a TMR equipment, micro-CT measurements (μCT 40; Scanco Medical AG, Bassersdorf, Switzerland) were made inserting these samples inside a whole tooth which was especially prepared in order to simulate a non-destructive evaluation. Also the effect of edge artefact was evaluated by using different threshold for the start of the lesion. Our observation showed the high Pearson correlation between both methods for evaluation of mineral loss and lesion depth and that the variation of the lesion parameter as 20 v% for the beginning of the lesion is a rational procedure. Above this value seems to be not necessary and 0 v% can lead to a higher variation of the values due to operator uncertainties within an artefact area. With respect to the use of micro-CT in dentin excavation research, it was a valuable tool to distinguish between the three mineralization phase in the carious process; a very high demineralised dentin, a layer of increasing mineralization and a sound dentin layer. In this chapter we have compared a new enzyme solution (SFC-V, 3M ESPE AG, Seefeld, Germany)for dentin caries treatment in comparison with a well established method (Carisolv™ Gel Multimix; MediTeam Dental AB, Gothenburg, Sweden). The use of the threshold technique for the evaluation of the removed and remaining dentin after excavation seems to be worthwhile. The mathematical model could very well compare both solution and the remaining thickness of demineralised dentin with additional insight into its three-dimensional perspective. In this work we tried to demonstrate the current possibilities of micro-CT imaging and quantification for the use in caries research. The system presents its limitation with respect to energy selection, scans artefacts, calibration and costs. However, our caries research domain demands a method which enables non-destructive analyses due to the dynamic characteristic of caries itself. The high correlation existed between the micro-CT system and the most reliable method of caries analyses stimulates the interest to persist the effort for the validation of the system. New research should be encouraged to evaluate the equipment for the studies of enamel abrasion and artificial caries in enamel and dentin. Moreover, real time experiments and three-dimensional analysis of mineral loss could be done as also morphological insight of the development of caries. Longer term experiments could be also stimulated using the most tempting advantage of the method, which is the possibility of conducting longitudinal studies without destroying the samples