Comparison of X-ray Microtomography with Transverse Microradiography for Assessment of Enamel Remineralisation

Transverse microradiography (TMR) remains the reference standard for assessment of enamel remineralisation, however it is destructive to the sample and precludes longitudinal analysis. X-ray microtomography (XMT) offers a non-destructive alternative, though its accuracy for remineralisation analysis relative to TMR has not been established. The objective of this study was to compare conventional Micro-CT (Cµ-CT), synchrotron radiation-computed tomography (SR-CT) and TMR for assessment of enamel subsurface lesion remineralisation by casein phosphopeptide-amorphous calcium fluoride phosphate (CPP-ACFP) in vitro.

Artificial subsurface enamel lesions created in extracted human third molars were divided into experimental and control halves; the experimental halves were exposed to CPP-ACFP for eight days. Measurement of percent remineralisation (%R) was calculated by scanning samples using Cµ-CT and SR-CT, and subsequently processing for TMR. Repeated measures ANOVA with Tukey HSD post hoc comparisons and Bland-Altman analysis were conducted to compare measurements.

Mean %R as measured by Cµ-CT (20.77 ± 7.12%) and SR-CT (20.55 ± 6.27%) were not significantly different but were both significantly lower than %R measured by TMR (49.29 ± 3.23%; p<0.00001). Significant differences between methods were observed for ΔZr (p<0.001) and ΔZd (p<0.02). Both XMT modalities were affected by imaging artefacts which compromised assessment of the enamel surface zone.

Both Cµ-CT and SR-CT underestimated enamel remineralisation relative to TMR though were equivalent in diagnostic value. TMR remains the more sensitive method for ex vivo remineralisation analysis, particularly for accurate measurement of the surface zone. XMT is more appropriate for non-destructive or longitudinal measurement of tooth mineral.

The clinical adoption of new remineralisation technologies is often based on ex vivo data using X-ray based methodologies. In this study, X-ray microtomography substantially underestimated enamel remineralisation relative to transverse microradiography. This indicates that use of X-ray microtomography may lead to underreporting of the efficacy of remineralising agents when used as the primary outcome measure. Transverse microradiography remains the more sensitive and accurate reference standard for ex vivo enamel remineralisation analysis.