Enhanced Transport of Materials into Enamel Nanopores via Electrokinetic Flow

Abstract

The ability to infiltrate various molecules and resins into dental enamel is highly desirable in dentistry, yet transporting materials into dental enamel is limited by the nanometric scale of their pores. Materials that cannot be infiltrated into enamel by diffusion/capillarity are often considered molecules with sizes above a critical threshold, which are often considered to be larger than the pores of enamel. We challenge this notion by reporting the use of electrokinetic flow to transport solutions with molecules with sizes above a critical threshold-namely, an aqueous solution with a high refractive index (Thoulet's solution) and a curable fluid resin infiltrant (without acid etching)-deep into the normal enamel layer. Volume infiltration by Thoulet's solution is increased by 5- to 6-fold, and resin infiltration depths as large as 600 to 2,000 µm were achieved, in contrast to ~10 µm resulting from diffusion/capillarity. Incubation with demineralization solution for 192 h resulted in significant demineralization at noninfiltrated histologic points but not at resin infiltrated. These results open new avenues for the transport of materials in dental enamel.

Enhanced Delivery of F−, Ca2+, K+, and Na+Ions into Enamel by Electrokinetic Flows

“…They claimed that different kinds of molecules can be transported onto the enamel surface, but no infiltration data were shown (Pitts et al 2009). Recently, the application of electrokinetic flow has been shown to enhance material transport into the pores of normal enamel (Gan et al 2015). It was shown that it takes only 3 h to replace the water content of a ground sample of normal human enamel with concentrated salt aqueous solution (Thoulet's solution), compared to the 1 mo needed to replace only 10% of water content by diffusion (Gan et al 2015).…”

High Amount of Organic Matter during Caries Formation Reduces Remineralization and Resin Infiltration of Enamel Caries

“…Our study suggests that replacement of organic matter and firmly bound water by resin infiltrant is key for improving caries infiltration and, hence, arrestment of lesion progression. In this case, when available pore volume is filled with water, not capillarity, but other transport processes (like electrokinetic flow) [Gan et al, 2015] will be required to get materials into enamel pores.…”

“…Histological sections were stored in 0.02% aqueous sodium azide solution before and after all analytical and experimental procedures. Histological sections were submitted to transverse microradiography [Gan et al, 2015]. Mineral volumes were measured at selected histological sites (15 × 15 μm) located along a transversal line traced following the prism paths in enamel caries lesions: at the surface layer and then at 20-µm intervals up to the deepest point in the caries lesion located closest to normal enamel.…”

“…In shallow lesions, 1-2 additional points at the surface layer were included. The Angmar formula [Angmar et al, 1963] and a mineral density of 2.99 g cm -3 [Elliott, 1997] were for mineral volume analysis [Gan et al, 2015].…”

“…Resin infiltration into subsurface lesions was analyzed performing Z scans under a confocal laser scanning microscope (model DMIRE2, Leica, Germany; excitation of 488 nm and emission peak at 510 nm) [De Sousa et al, 2017] exploring the autofluorescence of the resin infiltrant [Gan et al, 2015].…”