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.