Micro-scale Compositional and Mechanical Analysis of Primary Dentin

Objectives: To understand the relationship between micro-scale composition and mechanical properties of primary dentin using scanning acoustic microscopy (SAM), scanning electron microscopy (SEM) and micro-Raman spectroscopy (µRS).

Methods: Primary dentin mechanical properties have been widely studied; however, few measurements have been made with non-destructive methods at micro-scales. Non-destructive methods allow us to utilize other complementary techniques for property characterization of the same location. A second primary molar specimen exhibiting sound and caries-affected (c-a) regions was collected following normal exfoliation under an IRB approved protocol. Micro-scale acoustic impedance map of a section through this sample was acquired using SAM. Mineral/collagen ratios were obtained at the selected locations on the same section with µRS. Backscattered electron microscopy was used to obtain qualitative mineral density maps of the section. Careful calibration of each method was performed to reduce system effects and obtain accurate data. The information from these methods was combined to find the relationship between composition and mechanical properties. As a result, micro-scale physico-mechanical properties, at ~100 micron resolution, were obtained at 300 locations of the same sample of c-a primary dentin.

Results: The acoustic impedance ranges within 3.1 – 5.3 MRayl in the sound dentin region and 1.8 – 7.3 MRayl in the carious and c-a regions. The mineral content based upon PO₄/amide ratio of the c-a region is significantly higher than that of sound dentin. The grayscale values of backscattered SEM images corresponding to those regions range within 119-130 and 65–155 respectively.

Conclusion: The acoustic impedance of the c-a region is higher than sound dentin indicating increased elastic modulus. The increased elastic moduli of caries-affected primary dentin are correlated with the increased mineral density maps. These complementary characterization techniques allow us to correlate micro-scale structure/property relationships at the same location on biological specimens.

NIH/NIDCR DE014392, S10 RR16710, R13 DK069504